C£J,I.F'OP.N.TA
BT.i\~TE
UNIVERSITY 1 NORTHRIDGE
AU1'0tWHIC CON'l'ROL OF HEART RATE DURING HEATING AND COOLING
II
IN TURTLES
(PSEUDEHYS SCRIPTA EJ. . EGANE2)
A ti1esis submitted in partial satisfaction of the
requirements for the degree of lVlaster of Science in
Biology
by
Marris Elliot Berger
-
August, 1974
The thesis of Morris Elliot Berger is approved:
Committee Chairman
California State University, Northridge
August, 1974
ii
DEDICATION
This work is dedicated to my wife, Carol Ann Berger.
iii
ACKNO\"'lr.EDGMENT S
Thanks are extended -to members of the faculty and
staff at California State University, Northridge, for
their interest and loan of equipment and supplies:
Dr. Earl Segal, Dr. Jim Dole, Mr. Robert Botts and Ms.
Sarru1 Yucht (Biology Department) and Dr. Roy Griffiths
(Psychology Department}.
I also want to express my thanks
to Dr .. Richard Swade and Dr. Kevin Daly for their advice
on appropriate statistical methods.
I
especially want to express my gratitude to Dr.
Fred White, Department of Physiology, University of
California., Los Angeles, for his early constructive
comments and later review of the results, and to Dr.
Maylene Wong, cardiologist, Veterans Administration
Hospitali Los Angeles, for the loan of essential monitoring
equipment.
Drugs for this study were generously supplied
by Dr. Robert A. Maxwell .:>f Burroughs Wellcome Company
(Darenthin, bretylium tosylate) and Henry L. LeMien, Jr.,
of Ayerst Laboratories (Inderal, propranolol hydrochloride).
Finally, I would like to thank Dr. George Fisler and
Dr. John E. Kontogiannis for their review of the manuscript.
I particularly want to thank Dr. Richard Potter, my
research advisor, for his continual support and
encouragement during the course of this study.
iv
TABLE OF CONTENTS
DEDICATION • •
.
•
ACKNOWLEDGMENTS. •
•
• • • • •
...
• iii
•
iv
•
• • • •
LIST OE' ILLUSTRATIONS.
• •
•
•
• • • • •
LIST OF TABLES •
ABSTRACT •
•
INTRODUCTION • •
~ffiTERIALS
• •
.
• • •
0
• • • •
• • •
• •
• • • • • • •
• •
• •
• • • •
AND METHODS.
• • • •
• •
vi
viii
ix
..
1
•
3
Dose response ••• A·~················~··~
Heating and cooling ••••••••••••••• ~····
3
14
• • •
26
Acute dose response9•••••v•••••••••••••
Chronic dose response.~·····•••••••••••
Heating and cooling •••• "., •••••••••••••
26
26
31
RESULTS.
• •
• • • • •
DISCUSSION •
• •
•
• •
•
• •
•
Dose response •• a•••••••••••••••••••••••
Autonomic control of heart rate •••••• ~ ..
Circulatory and metabolic adjustments ••
Heating and cooling hysteresis •••••••••
Pharmacological blockade in mammals ••••
Central nervous control ••••••• o••••••••
Behavioral thermoregulation ••••••••••••
SUMMARY.
•
• • • •
LITERATURE CITED • • •
v
.
.
59
59
62
63
67
69
72
76
• • • • • •
80
• • • • • • • • • •
83
LIST OF ILLUSTRATIONS
Page
Figure
.,
.... ......
.L.
Special equipment •
2.
Chronic preparation
~A.
Dose response monitoring • •
e
• • •
.
• • •
7
• • • • • • •
• • •
9
•
•
•
•
•
•
•
0
..• • •
Honitoring during heating "
.. ....
Monitoring during cooling • . . . . . .
...
Heating turtle, head extended • . . . . . .
.
Heating turtle, submerged • . . .
...
Heating and cooling scheme.
.. ......
Dose response curve for atropine • • . . . . . .
Dose response curve for propranolol . . "' . "' .
Dose response curve for bretylium • •
. . .
12
3B. Equilibration prior to heating • • • •
12
4A ..
18
4B_.
SA.
5B.
6.
7.
8 ..
9.
~
~
•
3
.. .
lOA. Control heart rate variation, heating
.
lOB. Control heart rate variation, cooling
. .
llA. Hear·t rate response to drugs, heating
llB .. Hear·t rate response to drugs, cooling • •
12.
Control heart rate fluctuation No. 16 • •
13.
Heart rate hysteresis, atropine •
14.
Heart rate hysteresis, propranolol
15.
Heart rate hysteresis, controls
..
•
•
16.
Heart rate hysteresis, propranolol.
.
17 ..
Pooled hysteresis with atropine
18.
.
"'
"'
...
...
...
18
21
21
23
28
29
30
33
34
37
38
41
• • • • •
•
43
atropine
.
44
.
• •
•
45
• •
• •
.
46
• • • • •
49
Pooled hysteresis, propranolol. .. • • • • • • •
50
vi
.
&
..
. . • • . ..
• 51
19.
Pooled hysteresis •
20.
Diving controls, heating and cooling rates • • • 54
21.
Isoproterenol and atropine,
heating and cooling rates ..
22.
• • •
•
0
......•
Dead versus live, heating and cooling rates
vii
•
o
.. 56
•
58
LIST OF TABLES
Table
1.
Page
Heating and cooling experiments. • • • • •
V':i,ii
o
•
16
ABSTRACT
AUTONOMIC CONTROL OF HEART RA'l'E DURING HEATING AND COOLING
IN TURTLES (PSEUDill1YS SCRIPTA ELEGANS)
by
Morris-Elliot Berger
Master of Science in Biology
August, 1974
Autonomic control of heart rate during generalized
heating and cooling in water was studied in the red-eared
turtle, Pseudemys scripta
~legans.
Sympathetic blockade
with propranolol hydrochloride and parasympathe-tic blockade
with atropine sulfate were used to determine the relative
influence of each branch on heart rate changes during
heating and cooling.
Dose response curves were determined
for these drugs.
As the body temperature increases in turtles, the
parasympathetic branch of the autonomic nervous system
contributes more to inhibition of the heart rate than the
sympathetic does to its augmentation.
The coincidence
between totally blocked and unblocked heart rates in
ix
·turtles suggests that, unlike mammals, normal heart rates
are no·t displaced from the pacemaker rate by overriding
parasympathetic activity.
Significant, drug-induced
changes in heart rate were not correlated consistently
with changes in heating or cooling, suggesting that
heart rate does not have a direct
significance.
thermo~egulatory
Drugs which affect peripheral autonomic
control of vasomotor changes were responsible for altering
heating· rates.
Diving behavior was related to a reduction
in cooling rates and heart rates.
Diving bradycardia
was abolished by either atropine or propranolol blockade.
The hysteresis of heart rate versus body temperature
during heating and cooling was reduced by
and augmented by sympathetic blockade.
x:\
paras~npathetic
f"-····--····~--~---------~------·------------------·---~-----··--··---~------·
:'.
----,
I
INTRODUCTION
Both behavioral and physiological responses to
changes in environJnental temperatures have been
demonstrated for many species of reptiles.
Under
conditions of artificial heating and cooling, lizards
of the families Agamidae, Varanidae, Iguanidae, and
Scincidae can alter their thermal conductance in order
to heat faster than they cool (Bartholomew and Tucker,
1964; Neathers, 1971}.
The-cryophilic lizard, Sphenodon
punctatum, also heats faster than it cools (Wilson and
Lee, 1970).
Aquatic turtles were recently found to heat
fas·ter than they cool, whereas terrestrial species
showed the opposite effect (Spray and May, 1972).
Corresponding changes in peripheral circulation, namely
increased blood flow during heating and.decreased blood
flow during cooling, have been reported for the red-eared
turtle, Pseudemys scripta elegans (Weathers, 1971).
Little information is available as to the degree of
cardiovascular autonomic control of circulatory responses
to heating and cooling regimes.
Weathers
~
al.
(1970)
concluded that increased blood flow to the skin during
; heating in Iguana iguana and Tupinarnbis nigropunctatus
i
I was a result of sympathetically mediated vasoconstriction
i
i in
muscle.
This, they assert, is responsible for
i
L____________
1
l
__ _ _ _jI
r· --···-- ----------------··
! increasing the rate of
I
Indirect evidence
------~---·-
;
-'-----------------~---------------,
heat gain.
·
·
for circulatory adjustments with
l
i
,
a thermoregulatory function comes from heart rate
measurements made during heating and cooling.
The heart
rate of several lizards during heating is higher than
i t is during cooling at similar body temperatures.
Despite a high degree of variability of heart rate
associa·ted with respiratory activity, Weathers (1970)
was able to show that the heart rate during heating in
Pseude:mys floridana was strongly atropine sensitive.
-------~~~~~~
This suggests that a component of the heart rate during
heating i.s a parasympathetically mediated inhibition.
The normal resting heart rate in vertebrates is
a balance between sympathetic and parasympathetic activity.
' The present study was undertaken to determine both the
effectiveness of pharmacological blockade and its
usefulness in quantifying autonomic control of heart rate
during heating and cooling in the red-eared turtle,
I {Pseudemys
I
I
I
L
scripta elegans) •
f4ATERIALS AND METHODS
Dose response ·
Dose response curves were determined for three drugs
which interfere with autonomic activity, atropine,
propranolol and bretylium tosylate.
Intravenous doses
of these drugs were studied in conjunction with their
heart rate effects following direct nerve stimulation.
i
Effective doses were initially· based on the drug's ability
to overcome the antagonistic effects of direct nerve
stimulation.
Alternatively, when it was difficult to
obtain reproducible responses following direct nerve
stimulation, effective doses were determined by their
ability to maximally increase or decrease heart rate.
Turtles (1000-1800 grams) obtained from a biological
supply house (Nasco, Ft. Atkinson, Wisconsin) were
premedica·ted with chlorpromazine (Thorazine) administered
in doses of 10 mg/kg intramuscularly at room temperature.
Chlorpromazine caused varying degrees of relaxation and
tended to shorten the
induction time.
Ten minutes later
sodium pentobarbital (Nembutal) was administered in doses
of 17 mg/kg intraperitoneally.
Surgical anesthesia was
reached in 2-3 hours (modified from Kaplan, 1970).
'
The entire plastron was removed in order to facilitate
I
i the
positioning of stimulating electrodes both on the vagus
I
l
L-----~
-·--·-----_j
3
··----------··---·---···------··-----·--------·--------------~--------------1
and on or near the cervical (middle and inferior)
'
sympat:hetic ganglia, and to allmv direct visualization
' of the beating heart and catheterization of the abdominal
vein (Ashley,
Moale, 1881).
1962~
Gaskell and Gadow,
1884~
Martin and
Three shallow grooves were made in the
carapace 9pposite the right foreleg, left foreleg and
left hindleg for the attachmen·t of EKG leads.
Large
copper alligator clips and the liberal use of EKG paste
produced satisfactory contact.
The vagosympathetic trunk was exposed in the neck
by blunt dissection and kept moist with turtle Ringer•s,
: NaCl 6.8 g/1, KCl 0.29 g/1, CaC1 2 •2H 2 0 0.29 g/1, 15 ml
0.1 M Na2HP0 4 and 6 ml
6~1
M NaH 2Po 4 (Wilson, 1972).
The abdominal vein was fitted with a polyethylene catheter
with a three-way stopcock and tied off distally.
The
catheter was directed proximally 3-4 em and secured with
Ii black
I
silk ties.
Heart rates were determined by direct visualization
I
li of the beating heart, monitoring an oscilloscope trace
!
(Phipps and Bird, PB-M) or from a short EKG strip
(Sanborn, Model 100).
a
thermisto~
Body temperature was measured via
probe (Yellow Springs Instruments, Model 401)
inserEed 6-8 em into the cloaca and a continuous permanent
record was made en a strip chart recorder (Yellow Springs
:! Instruments, Telethermometer and Laboratory Recorder,
i
j
I
Model 80).
The nerves were stimulated with an electronic
1..--~-·~~--------~---·
._
5
square-wave
stimu~ator
(Grass Instruments, Model S6) in
ten-second trains with bipolar silver electrodes.
Alternatively, per cent maximum heart rate change
was determined for turtles fit.ted with a chronic
...
intravenous catheter and EKG electrodes mounted
permanently through the carapace.
EKG electrodes
were specially constructed using gold-plated brass wood
scre1,;s.
The shank was modified for soldering a
single-conductor, shielded wire to accommodate the .jaws
of;! a small wrench (Fig. lC)..
The completed electrodes
could be.screwed into the carapace through small pilot
holes spaced on the marginal bones opposite three limbs
(right foreleg, left foreleg and left hindleg).
Heat-shrink tubing and silicone caulking were applied
to the exposed threads.
These electrodes produced
signals with minimal somatic noise, their life time
limited only by excessive tension on the lead in the
unrestr·ained animal.
A heparin filled (1:500) polyethylene catheter
inserted into the hindleg femoral vein and secured to
the carapace at its free end with a large rubber band
(Fig. lB & 2}.
The technique for inserting the femoral
catheter was similar to the acute catheterization of
the abdominal vein.
However, in this case the longitudinal
dorsal incision exposing the hind limb vessel was closed
with surgical gut.
A specially constructed, loose-fitting
Fig. 1
Special equipment.
Polyethylene splint,
cut and shaped for turtle's hindlegs (A);
polyethylene catheter for chronic implant
(B)~
chronic EKG electrodes mounted in
carapace and fashioned from brass wood
screws, with modified.shank and complete
with shrink-tubing insulation (C).
7
Fig. 2
Chronic preparation.
Turtle with EKG
electrodes and catheter in place (P.) ;
close-up of catheter insert.ion site {B).
9
A
B
.10
rigid polyethylene cuff, extending from the foot to the
middle of the upper leg, was left in place for about two.
weeks to prevent flexion of the leg and relieve tension
on the wound (Fig. lA).
In several cases these cuffs
were left in place with no overt ill effects to prevent
catheter abrasion with the underside of the carapace.
Finally, the two proximal silk ties were anchored to
connective tissue adjacent to the vessel to act as a
strain-relief mooring preventing the vessel from tearing
during routine handling.
Heart rate and body temperature were recorded in
eleven turtles during a control period and following the
administration of test doses of atropine sulfate
(Burroughs Wellcome Co.), propranolol hydrochloride
(Inderal, Ayerst Laboratories) and bretylium tosylate
{Darenthin, Burroughs Wellcome Co.).
Body temperatures
were controlled by a circulating water bath at 25.0
c,
±
0.5
with animals submerged to the periphery of the marginal
bones measured at the bridge between carapace and plastron.
Following a staggered injection of drugs, up to 4 animals
could be monitored sequentially through the use of
specially constructed switchable EKG inputs and the
standard switchable Telethermometer (Fig. 3A).
About 10
beats were recorded every minute prior to the appearance
of the peak heart rate response and every 3 minutes
thereafter.
The intervals between beats were averaged
11
Fig. 3
Simultaneous monitoring during dose response
determinations for three turtles (A); turtle
equilibrating at 5 C in an ice bath prior to
heating and cooling (B).
...,_... ~..... --~-~·--·--.~............. _, ___ ~-----~·--~~-··~~~-~-~---·~·-----~·----····-~-----·-~-~"-··-~'":'~-·-·~.__---~~.-----····--- .. ~"1
l
; and converted to heart rate (beats per minute).
Heart
.
;
(
rate·was plotted as the maximum per cent change from
control values.
After a thirty-minute control period marked by a
stable heart rate and body temperature, drugs \vere slowly
infused o·ver a thirty-second period and the catheter dead
space fJ.ushed with
0.3 m.l).
0.9
per cent normal saline (about
The drugs were reconstituted ·.-dth 0.9 per cent:
sodittm chlor.ide or normal saline to concentrations greater
than co:rrunercially available, so as to reduce the final
dosing
1
vol~~es.
Single doses, administered on a total
body vleight basis (mg/kg) 'ir'Tere usually between 0. 5-1.0 ml
' final volume.
Propranolol hydrochloride was buffered
with ci·tric acid crystals to pH 3. 5 and like atropine and
bretylium solutions, transferred to amber multiple-dose
vials via a 0.22 p Millipore particulate filter.
The interactions of isoproterenol (4 pl) and
propranolol (1.0 mg/kg), and atropine (0.5-5.0 mg/kg)
and propranolol (0.5 mg/kg and 1.0 mg/kg} were examined
in a limited number of experiments.
I
Heart rate and
body temperature were monitored in a constant temperature
' bath as previously described for determination of dose
response curves.
!
serv~d
In the first series atropinized turtles
as controls for the administration of propranolol.
In the second experiment isoproterenol was studied before
and after beta-adrenergic blockade with propranolol.
1
L____________________ _
i
-----------------c·--------------·-----------l
14
Between experiments turtles were kept in individual
plastic tubs at room temperature and fed raw lean ground
beef, mealworms and lettuce 3-4 times per week (Kaplan,
1957).
Catheters were flushed with a heparin solution
{1:500) at least once per week.
Periodically, the plastic
stopcock (Pharmaseal, K-75) was replaced when leaks
appeared.
Heating and cooling
Seven turtles were treated with atropine and
propranolol during heating and cooling.
Four (Nos .. 2, 4,
6 & 9) had previously been used to determine effective
doses and were in good health, and three fresh animals
(Nos. 15. 16 and 171 were added (Table 1).
Turtles were
initially maintained at about 4.0 C for 12-24 hours,
partially submerged in
pl~stic
tubs in a refrigerator.
Prior to transfer to the heating tub, each turtle was
allowed to equilibrate to 5.0 ± 1.0 C for at least
fifteen minutes (Fig. 3B).
Partially immersed in a
40.0 ± 0.5 C warm water circulating bath, the turtle
was heated to a plateau body temperature of 37.0-38.5 C
(Fig. 4A).
Turtles were heated until no further change
was recorded in body temperature or heart rate, then
quickly transferred (less than 10 seconds) to the cold
bath.
In the 10.0 :
0.5 C cold water circulating bath
the turtle was cooled to a body temperature of
Table 1
Heating and cooling experiments.
aNumerals represent number of experiments
performed, while superscripts represent
modifications in individual experiments.
bExperimentals: ATRO.=atropine, PROP.=
propranolol, BRET.=bretylium, ISOPRO.=
isoproterenol.
cHeating body temperature overshoot.
dcooling body temperature overshoot.
ePropranolol initial dose doubled.
finitial dose supplemented with constant
infusion.
gisoproterenol and atropine.
hExperiment terminated prematurely.
r~---·---·-~,
. _. . .
·------~--~···---~-
. --·-;---- --···-···
I
lI
-
----·
TABLE 1. HEATING AND COOLING EXPERIMENTsa
i
I
I
TURTLE
WEIGHT (GMS')
CONTROLS
EARLY
LATER
II
l
1
1044
4
2
1195
4
2
3
1052
4
1
4
1461
4
1
2c
1
2f
6
1803
1
2
1f
2e
1
9
1722
4d
1
3
1
12
2213
1h
15
1327
2
1
1
1
16
1326
2
2f
1
1
1
17
1033
1
1
1
2c
1
16
10
10
11
I
TOTALS
ATRO.
PROP.
EXPERIN.ENTALSb
ATRO ./PROP , BRET.
NO,
.I " QIWI\!'III&JBDI
17
1
•
1
~WIHLliH*
- - - '
2h
ISOPRO.
DE.AD
W&
1!12&1
1
1
I
1
1
1g
1
2
2
2
'
I
asee opposite page for explanation of superscripts.
I._ ---·-· --
.. ····· ..
I
__.. J
.
...
m
1
,.-. "'
I
Fig. 4
Monitoring heart rate and body temperature
during heating (A}; cooling (B).
18
A
B
19
;<-"---·••--··~-·~~~-··-------
•••••-•--··-· -••-•• -~~~---~-u- ---·--~~- ~·-~--·---~-• -.-~·--»-·-~--·~--~~~ •-·--------·--·~·~>·- -- r--~---....--~~.·-••• •·•·-·-,
12.0-14.0 C (Fig. 4B).
Similarly, the experiment was
I
terminated when no further changes were recorded in heart
rate or body temperature.
! monitored
Bath temperatures were
periodically, whereas cloacal body te.mperat:ures
were recorded continuously as described for dose response
determinations.
Turtles were secured to aluminum blocks with rubber
straps and immersed to the level of the marginal bones
measured at· the bridge between carapace and plastron.
In this positioni the turtle's head and legs were free
to mo"Ve.
The unextended head and neck were partially
• immerSed, although the nostrils could clear the surface.
Tu.rtles could volu.ntarily submerge their heads completely
or extend their neck and head well above the surface (Fig.
SA, SB)e
Cellulose sponges were placed between the plastron
and aluminum block to minimize heat transfer between them.
Following a fifteen minute equilibration period at
5.0 ±
:1~"0
c,
drugs were administered in two successive
i half-doses, fifteen minutes apart (Fig. 6) •
I of propranolol, atropine and bretylium each
Initial doses
!
contained
I
I
1 mg/kg of drug.
Initial doses of a combination of atropine
:and propranolol also contained 1 rng/kg of each drug.
'
!Fifteen minutes after the second half-dose, the turtle was
j transferred to the heating bath.
!
A third half-dose was
: administered as a check on the effectiveness of the
l
•
•
•
! 1n1t1al dose after the heart rate and body temperature
l__ _. __ ~-----~·-·-
I
- - - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ,_ _ _ _ _ _ _ j
.20
Fig. 5
Heating turtles.
Heating turtles with
neck and head extended (A); and submerged
in a diving position (B).
21
A
B
22
Fig. 6
Heating and cooling scheme.
1.
Initial control period.
2.
Half the initial dose of drug injected.
3.
Half the initial dose of drug injected
and start constant infusion (if called
for).
4.
Transfer turtle to heated bath
(40 ± 0.5 C).
5.
Inject another half (initial) dose
as a check of the effectiveness of
blockade after heart rate appears
to plateauo
6.
Transfer turtle to chilled bath
(10 ± 0.5 C) when heart rate appears
to plateau.
7.
Terminate experiment after no changes
are observed in heart rate or body
temperature.
23
r----------~----···--·--··---·--·--·--.:.·~---------- - . ----···-----·--~----------·----~----~
l
I
HEART RATE (BPI'~)
I
~
-~
~
'
I
I
I
I
I
I
/
/
/
l.O.
./
,
./
I
'\
\
\
\
'
N
I
I
!...~----~
~
~
('Jo)
1
~
clffi AQQH
I
~
I
,.,...,.. ..;'
I
. II
I
J
I
i
i
!
.24
~·--··--·-·--·-
.. ·---------------·-----·-------------------·----·--·-----..-·-------·----,
1
~-
appeared to plateau,
In several experiments, the initial
I
dose was supplemented with a slow constant infusion
(O.OOS ml/min, 0.4 mg/ml) of a lower concentration of
the drug or drugs under investigationo
Each of the 7
turtles was studied from one to three times with each
dru.g (Table.!}.,
Turtles that were heated and cooled
without the influence of drugs served as controls.
In the early heating and cooling controls, heart
rate was counted every 3 minutes from an oscilloscope
trace.
In later controls and experimentals, both heart
rate and body temperature were recorded continuously.
The EKG signal was amplified and filtered (l0\'1 cut-off
0.1 Hz, high cut-off 20.0 Hz) with an EEG amplifier
(Brush Coupler-Preamplifier, Model 114307 02).
The latter
produced an R wave capable of reliably triggering a
tachometer (Brush Cardiotach, Coupler-Preamplifier, Model
11 4307 03} which was utilized in the beat-to-beat mode.
Heart rate in beats per minute could be read directly on
a strip chart recorden (Moseley, Model 680) with a
calibrated range of 0-100 bpm (!:beat/division).
This
. recorder was calibrated daily against both an internal
I
.
: signal and an appropriate range of signals produced by
j
la
j
.
portable, battery-operated integrated circuit calibration
.
Ii d evl.ce.
This device, in turn, was calibrated with a
i digital counter.
Il______..,
_ _j
25
-------------·-·---------·--------,
i
Other drugs and drug combinations were administered
!
in a limited number of heating and cooling experiments.
!
The heart rate and body temperature response to bretylium
tosylate (initial dose, 1 mg/kg) was determined in two
turtles.
Effects of isoproterenol (Isuprel, Winthrop)
alone (4 Jll) and a combination of isoproterenol (4 pl)
and atropine (1 mg/kg) were each studied in a single
:
I
turtle.
Also, body temperature was recorded during heating
and cooling in two freshly sacrificed and heparinized
i turtles.
Finally, one control turtle was studied during
heating and cooling in a cooling bath lowered from 10.0
to 5.0 C.
In this experiment, the heating and cooling
' temperature ranges were each 35.0
c.
The data obtained from heating and cooling experiments
i
I
i
were plotted graphically as heart rate versus time, heart
rate versus body
time.
temperatu~e
and body temperature versus
The pooled heart rate responses for the 7 turtles
were evaluated using Student's t-test.
I
I
I
,I
I
IL___________
____ j
RESULTS
Acute~~~eseonse
Atropine (0.5 mg/kg) was able to abolish completely
cardiac standstill produced by stimulation of the
vagosympathetic trunk (4 pulses/sec, 10 msec duration,
2.0 volts).
The
sub~equent
administration of propranolol
had no effect on atropine's ability to prevent vagal
rate~
inhibition of heart
Cardiac acceleration, following
stimulation of the inferior and middle cervical ganglia
'
and adjoining nerves and cardiac "twigs" could be produced
only irregularly.
In these cases, a 30-100 per cent
increase in control heart rate was obtained with
stimulation rates and intensities similar to those
producing vagal inhibition.
The control heart rates
in these turtles were generally lower than in turtles
which did not respond to sympathetic stimulation.
Chronic dose-response
Dose response curves were determined for atropine,
propranolol and bretylium.
An average 68 per cent
maximum heart rate change was produced by atropine doses
of 1 rug/kg (Fig. 7).
A progressive drop in per cent
heart rate change was observed with doses greater than
1 mg/kg.
An average 32 per cent maximum heart rate
26
Figs. 7., 8 & 9
Dose response curves for atropine, propranolol
and bretylium.
r··--------------------------------------~.--------------~-----------l-
1
ATRCPINE
i
•
oo-
l
•
40
~
w
(..!)
~
~
0
•
••
••
•
•
~
Er:
E5
::r:: 20
.
•• •
•
•
••
••
_______4P______________________________________________
_
•
10
•
•
l
0.5 0.25 0.5
[____________ _
1.0
WJC. (rrb/KG)
2.0
5.0
29
--·------·--1
j.
!
PROPR~"JOLOL
•
••
••
30
.I
I
I
I
I
•I
I
I
I
I
•
~
e::::
I
I
II
~
~
j
iI
'
1
'
~
~
20
N
I
'
I
•
• •
•
::c
I
•
!
;
I!
l
• •
10
f
I
0.2
L_________
0.4
1.0
cooc
I
J'
2.0 .
(MJ/KG)
- - - · -
30
-----"---l-
r·-~"--~--~--------····-·--------------·--
1
I
BPfTYLI UM.
l
1
.I
I
40
20
0
•
••
•
••
•
•
•
•
I
I
I
I
Ii
I
•
I
-~::~--------------------~----------~--------------
•
•
I
I
•
70
I
. I
lI
I
I
I
I
L______
3.0
0.5 1.0
erne.
<fiGJKG)
10.0
__j
i
31
decrease was produced by similar doses of propranolol,
1 mg/kg (Fig.
8)~
A 1 mg/kg dose of bretylium tosylate
also produced an average 25 per cent maximum increase
-in heart rate (Fig. 9).
The interaction of these drugs was studied in
supplemental experiments.
Propranolol was found to
reduce the heart rate response of atropinized controls
40-150 per cent (4 turtles, 3 trials each).
Propranolol
also reduced the half-life of the heart rate response
to'isoproterenol from 53 minutes to 13 minutes.
Heating and cooling
The results of the early controls were based on 17
heating and cooling experiments, in which as many as 4
trials were completed for each turtle.
Despite the
subsequent repetition of these controls, using improved
heart rate recording techniques, these results have a
bearing on the variability of the individual turtle
response.
In duplicate determinations, individual turtles
were characterized by similar heart rate maxima during
heating.
Other heart rate responses which were more
characteristic of a particular turtle than the general
population include:
(1} the interruption in the rising
heart rate, when it briefly levels off or drops before
increasing again with body temperatures (Fig. lOA),
32
Fig. 10
Heart rate versus body temperature variation
in controls during heating (lOA) and cooling
{lOB).
(1) heart rate levels off or drops
briefly despite increasing body
temperature.
(2) progressive bradycardia near
maximum heating body temperature.
(3) profound, transient cooling
bradycardia followed by recovery
to temperature dependent heart
rate levels.
-.
~-
......
33
POOLED LA1ER CONTROLS nF-7)
70
HEATING
::::~:RANGE
-MIDRANGE
60
50
--
::2::
Eb
............
~
~
40
52
.i35
::.c
30
20
10
10
I
l_ _ _ _ _ _ _ _ _ _ _
40
I
__ j
34
1.
<--·-·-·---.--------··-·-- ------"-·-----·---------··-------··-----------..-----------..
70
it
POOLED LATER CONTROLS CN=7)
COOLING
RPNGE
I
;;:
1
/i'
,,,;:;::•:•:•:
l'il l 11ill~llli!
~~GE
.-:·:·
-:•:•:•
60
.;•:·:·:·:·:···
.:::::::::•::--:::::••::•··
::::::•:
50
::::::::
/:
'-
::::;:
,-....
'5.-
:::::::::::
_:';:: :•:::;::::
~ LiO
:::::::?
'-"
j.'
{
::
;::;:::
~
i':??i.
:::•:•:•
'--
~
,,:;::
L1j
:::c
..::;:::•:
:::::::
?I
•:::::· i'•':
30·
,(''iii!
::::--:
::::::::::::::::::::::
;:,:::·
/}•::::::::::::::;:::
:;::•t
:::::::
::::...
20
__::::::
{}':::::;::
,:;:;:•:::::::::•
::::::::::::::::::
::::::::::::::::::
10
}
::-':'
·::::;:
•::::
'
10
IL___________
20
30
'·
...
40
_____j
l
l
.
35
{2} the progressive bradycardia near the maximum body
temperature (Fig. lOA) and {3) the abrupt and profound
transient bradycardia (i.e., a heart rate drop of
30-50 beats/min) observed at the onset of the cooling
phase, whereas in duplicate trials the heart rate falls
from higher values (Fig. lOB).
A total of 53 heating and cooling trials comprise
the later controls and experimentals.
It is difficult
to pool the responses to each drug for the 7 turtles in
the group because of the absolute differences in heart
rate at comparable times and body temperatures.
Nevertheless, pooled heart rate responses suggest significant drug effects (Fig. 11).
The pooled atropine heart
rate during heating is significantly greater (P< • OS)
~~an
control, propranolol-atropine and propranolol pooled
heart rates during heating (Fig. llA).
In only one
determination at 60 minutes, mean propranolol heart rates
during heating were not significantly different from
control heart rates.
However, the relative position of
the means for the propranolol heart rates during heating
also suggest that the drug's effects are significantly
different.
In like manner, the heart rate response
during cooling was significantly greater than the
comparable propranolol response (P-<.05).
It was observed
that the pooled means for control and propranolol-atropine
heart rates during heating intersected and overlapped
36
Fig. 11
Pooled (N=7) heart rate responses to blocking
drugs during heating (llA) and cooling (llB).
.17
----- - - - ...
1
I
I
.I
I
I
i
i
I
I
I
50
I
30
HEATING
• ATRCFINE
o CCNfROL
a PRCFRANOLOL M'ID
ATROPINE ,,
• PRCFRANOLOL
±~'2
I
Si E.
I
·I
i
30
i
I
Il________
,
60
TIM:
~
<r~UNS I)
120
f
J
38
r- --·
_£....,..._
- - - - - - - - - - - - - · · ··----·------· - -
.
-------~Ill
·--------·-·--
!
i
I
I
I
!XXlLING
• ATROPINE
70
I
I
I! ..
!
o
a
60
I
CCX\rrROL
PROPRANOLOL AND .
ATRCFINE
• PROPPftNOLOL
!Ml.l ± :2 S. E.
50
20
i
I
I
I
. 10
I
I .
I
I
lL__ _ _ .----
30
60
Tit{:
90
C~UNS)
J20
'
I
J
39
at several points.
Continuous recording of heart rate revealed in all
controls fluctuations characteristic of individual
turtles (Fig.
12)~
Characteristic amplitudes and
frequencies varied within the experimental population
from 10-20 beats/min, every 1-5 min.
These fluctuations
were not observed in experiments with atropine or
propranolol.
In duplicate trials, heart rate fluctuations
were consistently correlated with periodic head
submergence.
Heart rates progressively fell to a low
level after head submergence and recovered rapidly with
emergency (Control A, Fig. 12).
Diving heart rates
ultimately recovered to non-diving control levels
following emergence.
Some turtles submerged repeatedly
during cooling with each successive episode characterized
by marked heart rate changes.
In graphs of the heart rate versus body temperature,
the heart rate changes during heating and cooling indicate
th~t
the blocking drugs cause a specific shift in the
dependence of heart rate on body temperature (Fig. 13-16).
At comparable body temperatures, atropine heart rates
were higher than either propranolol-atropine or
propranolol heart rates alone.
Similarly, propranolol-
atropine heart rates were higher than propranolol heart
rates alone.
The dependence of heart rate on body
temperature was more variable in controls than in the
40
Fig. 12
Control heart rate variation during heating
and cooling in turtle No. 16.
Cooling
control B demonstrated initial abrupt diving
bradycardia, in contrast to the gradual
heart rate drop in control A.
The heating
phase of control B coincided roughly with
control A and was omitted for clarity.
41
_J
<
j:Q
_J
-'
q
~
~
L>
0:.
§
w
g
C>
~w
•
_J:;:::::
a ........
~~
~
~ &:t:i:
~ ~ ~
!;;: CL CL
• • a
:2:
...........
C>
~
_...
(/)
z
.........
C>
en
~
'-"
~
.........
i-
I
I
1L ______ _
(Wda)
31\td lmt3H
---··-----------
II
________j
·.. 42
.1
Figs. 13, 14, 15 & 16
Changes in the hysteresis of heart rate
versus body temperature during heating and
cooling in turtle Noe 15 with atropine (13),
propranolol and a-tropine (14), control (15)
and propranolol (16).
.43
·-----·--------------·--·-·----·
,---·-··-··-----~-----------..
!
ATROPINE NO. 15
• HEATING
o COOLING
:
l
1
I'
'
!'
70
o
:}
..
••
•
oe
•
•
•
••
•
•
• ••
60
••••
0
50
0
•
I
0
I
0
0
•
0
0
•
30
0
0
0
0
20
00
•
00
00
0
10
•
10
20
30
BODY TEMP. <oC.)
l
40
!
J
44
r··---~
. ·---------------.----------------------·-·-·--·-- --·-···-··-------·----·---------------------·1
PROPRANOLOL AND ATROPINE NO. 15
• HEATING
o COOLING
70
I
.
1
• •
•
••••
• •
. . .0
•
50
•
•
•
•
• ••
0
0
•
0
30
0
•
0
0
0
20
0
0
0
0
oo
ooo
00
00()()()
000
10
I
•
•
•
10
20
30
BODY ID'P I coc I)
·---------··-·····--··---····-· .
40
... __________________ j
I
45
r·--i
~-----------·------·-··--·--·-----·-------------
.
I
i
l
ClliTROL NO J5
• HEATING
o COOLING
I
70
!
II
--------------._____________. .
..•••
.••• •
.• o
•
60
I
. . ..
I
••
••
0 ...
~
I
•
li
•
•
l
j
•
0
0
0
•
0
0
0
0
0
0
0
oo
0
0
0
20
coo
00
0
00
eoo
00
0
20
. BODY IDP
30
0
1
(
(.)
40
46
------------------··---,
PROPRANOLOL NO J5
• HEATING
o COOLING
I
70
I
60
..•
0
••••
•••
••
50
;
....
• • •
•
30
•••
••
•
I
I
I
0
-I
0
I
I
•
0
0
•
0
20
0
0
0
0
0
0
0
ooo
GOO 0
000
10
•
•
10
l
20
30
BODY TEMP. (°C.)
40
47
experimentals during heating and cooling
(Fig~
17-19).
Heart rate's dependency on body temperature during cooling
in controls was further complicated by the effects of
diving bradycardia.
The hysteresis (i.e, the lack of coincidence between
heating and cooling heart rates at similar body
terr~eratures)
of heating and cooling controls was reduced
by atropine and augmented by propranolol (Fig. 13-17).
This is also seen in duplicates of atropine, propranolol,
and control determinations (Fig. 17-19).
Hysteresis was
also demonstrated in a single experiment where the
heating and cooling gradients were adjusted to the same
absolute temperature (i.e .. , 35.0 C).
Heart rate at any
given body temperature was higher during heating than
during cooling.
The rate of heating was also about 12
per cent higher than the rate of cooling.
In considering body temperature versus time, no
single drug regime was consistently responsible for
specific increases or decreases in heating or cooling
rates.
However, atropine or atropine-propranolol was
always associated with the highest heating rates.
Control rates of heating and cooling were more variable
than the experimentals in duplicate determinations and
between different individuals.
However, cooling rates
were lower in controls characterized by diving bradycardia
(in 4 out of 7 turtles) than in non-diving duplicates
.
-----
..1, .g.
....
Figs. 17, 18 & 19
Pooled changes in the heart rate versus
body temperature hysteresis during heating
and cooling in turtle No. 16 for atropine
(17), No. 9 for propranolol (18), and
No. 9 for controls (19) •
.-
·~
r--'·--~--~-----------
----------·------·-··---------·--.o
1
l
...••..
POOLED ATROPINE NO. 16
• • HEATING
a o COOLING
i·
';
70
••
•0
....
•
.......• •
• •.a
e
II
II
·'
60
i
•
a
e•
•
•
••
••
•
0
a
0
a
0
a
0
a
a
o a
•
0
a
0
••
30
•
0
•
•
• •• •
a
oa
a
0
o
a
o a
0
o a
o a
o a
•
~a
00
ooa
ooa
~
•
• aa
aa
aa
10
I
I
••
..
•
1
I
I
10
L------------------------------
40
50
~~···--·--------·
POOLED PROPRPNOLOL NO 9
•• HEATING
ao COOLING
I
I
70
I
•
60
.rl':
....
• •
...•...•
. .0
' ~-···
•
I
50
••
•
•
•
•• •• •
•
•
0
0
0
0
•
•
•
30
I
0
0
0
••
0
••
20
a
a a
I
a
0
a a
a
0
a
0
I
a o
aoa
••
!
I
.I
l
!
IL ____
10
I
i
~
aa
o
o a o
aao o
ao8o
I
d;@
•
• •
•
ac@oo
a.oo
Qx)
a
10
20
30
BODY TEMP. (oC.)
40
51
r_____________:____________________
------------~----.
l
CQ\JTROLS (POQLfD) NO 9
. -. -
I
.
• • HEATING
a o COOLING
70
I
I
. I
:
....
....•
.. • ..••
• ••
•
• ••
I
!
I
I
•
60
a
I!
!
••
50
•
..
••
•
••• • • •
• • ••••
a• a •
•
••
•
o a
•
•
• •
30
0
0
•
a
0
ooo
0
a
•
a
0
a
ooo
20
a
0
ao
•
a<a
a
a
0
00 00
!_:~ 0
a aafl>
••
10
I
:
ll__
I
I
I
0
I
I'
------: ---------l
•
a ao
aa a
a a
aa
a
a
0
0
•
10
20
30
BODY TEMP. C°C.)
40
II
I
52
~--~
!
---- -----
-----------~-----------------------------------------------l
(Fig,. 20).,
1
I
A limited number of experiments with other drugs
administered during heating and cooling indicated that
heating rates may be altered by an alternative drug
combination.
Isoproterenol, administered with and
without atropine, was associated with increased heating
rates in the two experiments attempted (Fig. 21).
Bretylium tosylate produced contradictory heating and
cooling heart rate responses in the two experiments
attempted.
A comparison of heating and cooling rates in live
and dead turtles was instructive.
Live turtles heat
about twice as fast as dead turtles.
Cooling rates
were more alike than heating rates (Fig. 22).
l
I
I
I
I}
I
L__
___j
-
Fig. 20
Body temperature changes in diving and
non-diving controls for turtle No. 9
during heating and cooling.
. 54
---...-o:o
30
HEATING NO. 9
20
!
CCNfROLS:
. I
I
--- DIVING
- · Na\IDIVING
NcruJIVING
I
I
i
10
I
i
l
>
u
0
-
'-"
~~L-~---+~~--~--
30
I
l
''
''
90
60
30
120
COOLING NO. 9
''
"'
.......
......
,
-- ....
................
__ _
10
·II
0
I
L----
___j
'55
Fig. 21
Body temperature changes with isoproterenol
and atropine during heating and cooling in
turtle No. 6
.56
,- ·---··- -----·----·-------·-------.----------·-----·---------------,
I
I
~
I
30
HEATING NO. 6
20
- - CO'ITROL A
- CCNrROLB
___ ISa:>ROlERENOL AND
ATROPINE
10
30
I
!
60
90
120
COOLING NO. 6
.
!
20.
10
II
I
.____,...
0
J
57
Fig. 22
Body temperature changes during heating
and cooling in dead versus live turtles.
<;;
r----------------.-·------·---------·-------------~-----------·l
,.·
40
'1I
l'
i:
l
30
I
I
,
I
.,. /
1
I
,. .....
--
----~
/
/
/
20
/
HEATING NO. JJ
/
/
COORDLS:
/
/
-
-
/
-ALIVE
/
w.
........
"·~
v
/
Tlrv£ CmNS)
0·
40
30
20
II.
l~.
10
0
~
60
30
§
I
---I1AD
/
10
0
I
I
~
.....
''
120
COOLING NO 17
I
''
''
'
.....
----
__j
r-·-----.. ----~------------"-··-------~---------·--·-----------------l
I
.
i
DISCUSSION
Dose
r~Sjlonse
Atropine is known as an antimuscarinic agent because
i t inhibits the actions of acetylcholine on structures
innervated by postganglionic cholinergic nerves and on
smooth muscle that lack cholinergic innervation (Innes
and Nickerson, 1970).
The major action of atropine is
a competitive or surmountable antagonism to acetylcholine
(and other muscarinic agents) which can be overcome by
increasing the concentration of acetylcholine at the
receptor sites of the effector organ.
Only in high doses
does atropine produce blockade in autonomic ganglion
cells.
My data suggest that intravenous atropine in
doses exceeding 1 mg/kg produces a progressive blockade
of autonomic ganglia with a eoncommitant fall in heart
rate in
~-
scripta elegans.
Atropine doses of 1 mg/kg appeared to have the
greatest antimuscarinic effect.
Atropine (0.5 mg/kg)
prevented any cardiac slowing in response to direct
stimulation of the vagus nerve.
Additional doses of
atropine {0.5 rng/kg) administered during heating did
not produce any further heart rate changes, indicating
1
that completeness of the blockade produced by the initial
I
1
I
dose.
White also found that 1 mg/kg of atropine was an
·------------
L
59
i
··-··------'
61}
effective antimuscarinic dose in
Alliaato~
mississippiensis
{Personal communication).
Propranolol hydrochloride is a selective
beta-adrenergic receptor blocking agent.
Based on
the order of potency of five sympathomimetic amines
on various organ systems and muscle preparations,
Ahlquist (1948) proposed the concept of two types of
adrenergic receptors.
ro~inly
The alpha type is associated
with excitatory functions:
vasoconstriction,
stimulation of the uterus and nictitating membrane, etc.
The beta receptor is associated with most inhibitory
functions:
vasodilatation and inhibition of uterine
and bronchial musculature.
One important excitatory
function for beta receptors is myocardial stimulation.
For example, epinephrine is the most active mediator
of vasoconstriction and isoproterenol the least active,
whereas the reverse was true to cardiac chronotropic
responses {Ahlquist, 1948).
Black et al. first described
the beta-adrenergic blocking action of propranolol in
1964.
Subsequent studies suggested that propranolol and
its analogues block the cardiac effects of sympathomimetic
amines that.act on beta receptors (Barrett, 19701 Dunlop
and Shanks, 19681 Shanks, 1966a, 196Gb, 1967).
In my
experiments, propranolol significantly reduced the
positive chronotropic response to large doses of
isoproterenol.
61
I
··-------~
~~.---~---~-~~~~----
Propranolol, like atropiner is a competitive
i
I1 antagonist whose
blocking action may be prevented by
l
high concentrations of mediator.
Yet, in effective
doses, prop.J:anolol blocks cardiac responses to both
direct and reflex stimulation of the sympathetic nerves
in the dog (Ledsome, 1965).
My data suggest that
1 mg/kg is an effective dose for blocking sympathetic
influence on the heart in the turtle.
The reductions
in hear·t rate with propranolol probably resulted from
a block of resting sympathetic tone to the heart rather
than an increase in parasympathetic inhibition, as
reductions still occurred after the administration
of a tropine.
Atropine and propranolol have recently been used
to produce combined parasympathetic and beta-adrenergic
blockade in man as well as dogs (Jose, 1966: Jose and
Collison, 1970: Jose and Stitt, 1967, 1969: Jose and
! Taylor,
I the
1969).
Jose and collaborators suggest that
heart rate following complete autonomic blockade
l with atropine
and propranolol corresponds to the intrinsic
!
heart rate (IHR).
The IHR is that frequency at which
I the heart beats without nervous
Il It also has been suggested that
I to
or neurohumoral control.
the IHR is closely related
the cardiac pacemaker rate.
l
l
'
I
I
L--------'---,..----------------
62
Autonomic control of heart rate
As ·the body temperature increases in turtles, the
parasympathetic branch of the ANS contributes more to
inhibition of ·the heart rate than the sympathetic does
to its augmentation.
Furthermore, the control heart rate
during heating is not significantly different from heart
rates in turtles treated with
propranolol~~atropine.
In other words, the control heart rate appears to coincide
with pacemaker rate (i.e., IHR or totally blocked heart
rate) despite varying contributions from both branches
of the ANS.
In contrast, in humans (Jose et al., 1970)
and dogs (Jose, 1967), the IHR is significantly higher
than resting· heart rates, demonstrating the parasympathetic
domination of heart rate.
The coincidence between
·totally blocked and unblocked heart. rates in turtles
suggests that, unlike mammals, normal heart rates are
not displaced from the pacemaker rate by overriding
parasympathetic ac·ti vi ty.
In the following discussion, I will correlate my
results with existing evidence for autonomic control of
thermoregulatory responses in reptiles.
Evidence comes
from di.rect measurements of circulatory changes and
inferences based on the heating and cooling hysteresis
of heart rate versus body ·temperature and body temperature
versus time during heating and cooling.
Our more complete
63
understanding of sympathetic-parasympathetic.interactions
in mammals suggests that useful comparisons may be made
with evidence for similar interactions in reptileso
This approach also suggests that, in reptiles, there is
a basis for central nervous control of thermoregulatory
responses.
Reptiles in thermally complex environments
appear to have similar physiological capacities to alter
rates of heat exchange.
These
phy~iological
responses
.appear to complement such behavioral adaptations as
basking and breath-hold diving.
Circulatory and metabolic adjustments
Bartholomew and Tucker (1963) have suggested that
changes in circulation and metabolism are the two most
important factors contributing to alterations in the
rate of heating and cooling in lizards under experimental
conditions.
It is unlikely that heat production in the
turtle is sufficient to accelerate heating or diminish
cooling, although changes in endogenous heat production
have been reported for P. scripta elegans during diving
(Jackson and Schmidt-Nielsen, 1965).
Bartholomew and
Tucker {1963) found that metabolic heat in some lizards
· can account partially or completely for the differences
in
~eat
exchange during heating and cooling.
Evidence
for circulatory changes in turtles shows that both
cutaneous and carapace blood flows increased in response
to heating and decreased in response to cooling in
~eude!ll:fS
floridana and Chelydrf;i serpentina (Weathers
and White, 1971).
Cutaneous vascular responses to heating
and cooling have been similarly described for Ctenosaura
!l~ilopha
(Weathers and 1-!orgareidge, 1971), Dipsosaurus
dorsalis (Weathers, 1971), Arnblyrhyncus cristatus
{Morgareidge and White, 1969a) and Iguana iguana
{Morgareidge and White, 1969b).
Heath (1968) observed
perfusion changes following application of hot towels
to the plastron of a soft-shelled turtle (Trionyx
~ ..
).
Circulatory changes associated·with intracardiac
: and cephalic shunts also appear to have a thermoregulatory
role {i.e., alter heating and cooling or cooling rates)
in reptiles (Tucker, 1966).
Venous shunting has been
reported during diving in Pseudemys scrieta (White and
Ross, 1965) and Alligator !!!_ississippiensis and during
thermal loading in
Whi·te, 1970).
!•
iguana and Tegu
~·
(Baker and
Heath (1964) reported evidence for shunts
in the cephalic sinuses of Phrynosoma sp.
Onset of
shunting in the diving turtle is correlated with increasing
pulmonary vascular resistance following depletion of
oxygen stores in the lungs.
!•
Right to left shunting in
iguana during thermal loading causes venous blood to
bypass the lungs and enter the left systemic arch,
significantly increasing cardiac output (Tucker, 1966).
II Right
L ____
to left shunting would tend to reduce heat losses
I
__]
65
across the pulmonary vascular: bed and lead to the
increases in heat gain during heating.
It is unlikely
that the·short, voluntary dives reported here produced
shunting due to depletion of available oxygen stores.
Jackson and Schmidt-Nielsen (1965) noted that during
short dives lasting 30 minutes or less P9
script~
elegans
(150-350 gms) utilizes oxygen stores present in the body
for normal oxidative metabolism.
Consequently, if
shunting occurred in my experiments, it was probably
in
~esponse
to thermal loading and, not diving.
The effects of a variety of drugs on circulatory
responses to heating and cooling have been used as evidence
for autonomic control of thermoregulatory adjustments.
In my experiments, heart rate fluctuations during heating
were abolished by atropine or propranolol.
Weathers
(1971:704) observed a "strong dependency of heart rate
on respiratory state" in P. floridana and
c.
serpentina.
The fluctuation of heart rate during heating has been
correlated with periods of active ventilation and relative
apnea.
Heart rates are reported to decline during periods
of apnea, which are frequently interrupted by periods of
active ventilation (Weathers, 1971).
In several turtles
in my experiments heart rate fluctuations were associated
with submergence (low heart rates) and emergence (high
heart rates).
A more pronounced bradycardia sometimes
was triggered by the onset of cooling.
Diving bradycardia
65
r··
l
-----""--"··-~-----·-----
,in P.
~
elegans (White and Ross, 1965), like
'
'
shunting in A,. mississippiensis (White, 1970) has been
shown to be under parasympathetic control, for it is
abolished by atropine.
Bretylium tosylate, administered to D. dorsalis
in high doses (10 mg/kg, intraperi toneally) '1/las found
to have a significant effect on both heart rate and
body temperature changes (Weathers, 1970).
Bretylium
produces sympathetic blockade by accumulating in adrenergi~
nerves, preventing the release of norepinephrine in
response to nerve activity.
Weathers {1971:51) noted
that the hysteresis of heart rate versus body temperature
in D. dorsalis was not sensitive to atropine, concluding
that heat exchange in lizards may be affected by changes
in sympathetic tone (i.e., bretylium) whereas
~intact
parasympathetic innervation seems unimportant".
in
D~
However,
dorsalis 44 per cent of the difference between
heating and cooling rates could be attributed to endogenous
heat production (Weathers, 1971).
i with
I
Although my results
bretylium (1 mg/kg, intravenously) are inconclusive,
I atropine
was found to reduce significantly the hysteresis
· of heart rate versus body temperature during heating and
cooling.
These differences suggest that autonomic control
of heart rate may vary in reptiles during heating where
: endogenous heat production accounts for a significant
I
i
1
amount of the heat gain.
L
l.n my experiments, the ability
I
"_j
67
of isoproterenol and atropine to increase significantly
the rate of heating also suggests that peripheral
circulatory changes have a thermoregulatory-role in_
turtleso
Isoproterenol is a pure vasodilator agent in
man and appears to have a similar effect in the turtle
{Meyers,~
Heating
al., 1970).
an~cooling
hysteresis
The hysteresis of heart rate versus body temperature
during heating and cooling as a claim for active vasomotor
control has been challenged by some investigators
{Spray and Belkin, 1972).
Their arguments would also
apply to conclusions based on the body temperature versus
time (i.e., heating or cooling rates) hysteresis.
Heart
rate hysteresis is not apparent in experiments where
heart (i.e., pericardia!) temperatures replaced cloacal
body temperature measurements.
Spray and Belkin (1972)
go on to suggest that the heart rate hysteresis based on
cloacal temperatures represents a thermal lag or thermal
inertia of the tissue rather than active control.
Accordingly, these workers have demonstrated significantly
different time constants for temperature measured from
the cloaca, head, heart, lungs and nostrils of I. iguana
and Ctenosaura hemilopha under conditions of artificially
applied heat (Spray and Belkin, 1973).
Consequently, the
time constant for an animal's temperature response is
68
dependent on the experimenter's choice of measurement
sites.
Yet, ·the preceding observations do not exclude
the possibility that regional temperature differentials
are attributable to local differences in tissue
conductances in response to local vasomotor tone changes.
The hysteresis of heart rate versus body temperature
or
~the
association at the same body temperature of heart
rates of greater magnitude during heating than during
cooling" has been an indirect indication that circulatory
factors contribute to heating and cooling differences in
reptiles (Morgareidge and White, 1969:590).
During
generalized heating in man, heart rate increases are
thought to be a reflex response to shifts in circulating
blood volume to the periphery.
Morgareidge and White
(1969) noted that Amblyrhynchus cristatus appears to
p~cduce
heart rate changes secondary to shifts in
circulation.
It was observed in A. cristatus that
localized vasodilatation and vasoconstriction in regions
undergoing heat flux had no correlation with heart rate
or skin temperature changes elsewhere.
Also, it was
found that local heating and cooling of the dewlap of
!•
iguana following infiltration with lidocaine or
ganglionic blockade with pentolinium still produced
local circulatory adjustments (Morgareidgeand White,
1969b).
The aneural nature of vasomotor changes under
localized heating conditions suggests that heart rate
69
r····-·-··--·----·-----------------·- - - - - - - . - · · - - - - - - - - - - - - - - - - - - - - - - - - . ,
j
I
l) hysteresis must also be interpreted in terms of secondary
..
!
1
heart rate changes dependent on heating conditions.·
The results of my experiments suggest that the
generalized heating and cooling heart rate hysteresis
has a neural component.
increased by
The hysteresis appears to be
pa~asympathetic
sympathetic activity.
activity and reduced by
In other words, withdrawal of
vagal inhibition with atropine significantly decreased
the difference between heart rates at the same temperature
during heating and cooling.
The withdrawal of sympathetic
augmentation had the reverse effect.
It is suggested
by direct evidence from other reptiles (i.e., P. floridana,
C. serpentina and
£·
dorsalis) that this hysteresis may
reflect reflex adjustments in heart rate in response to
cardiovascular changes in the periphery.
Spray and May
(1972} suggest that the heating and cooling heart rates
in Chrysemys picta are dependent on an intact nervous
system.
Although the intact
£·
picta heats faster than
i t cools, denervation of the carapace (i.e., sectioning
of the dorsal roots of the spinal nerves innervating the
carapace) eliminated the hysteresis (Spray and t1ay, 1972) •
, _Pharmacological blockade in mammals
The present work is probably the first demonstrated
use of combined sympathetic and parasympathetic blockade
· for studying thermoregulation in reptiles.
I
L------·
Yet, various
·----------------------
__j
70
aspects of homeothermy in a few laboratory mammals (rat,
dog, rabbit, mouse and guinea pig) have been examined
utilizing a wide range of drugse
sp~cifici ty
In many cases the
of ·these agents was determined in the very
same species of test animalo
Maickel (1970) reported the body temperature changes
in rats exposed to 4
c
a variety of drugs.
These drug and drug combinations
for 4 hours given prior doses of
included sympatholytic agents, amine releasers,
ganglionic blockers, etc.
It was concluded that the
periphe1:-al sympathetic. system is important in
thermoregulation, but that the involvement of the
peripheral cholinergic component is necessary to
maintaining a normal thermal balance.
Maickel suggests
that the sympathetic nervous system is the messenger
control unit for the mobilization of calorigenic substrates
from storage sites and that the parasympathetic nervous
system is the messenger control system for the utilization
of calorigenic substrates in the production of cellular
heat.
Walsh {1969) studied heart rate changes in normal
beta-receptor blocked and atropinized rats previously
anesthetized with sodium pentobarbital, then heated from
24 C to thermal death.
Walsh calculated the pacemaker
rate from simultaneous solutions of equations for
atropinized and beta-blocked heart rates rather than
utilizing a combination of drugs to produce total
71
r------·---·-·-·· -.----··-·---------------·--------------------~----~-------------,
1
!
autonomic blockade.
As in the turtle, atropinized heart
'·
rates were always greater than.beta-blocked heart rates,
although the (heating) heart rate in the blocked rats did
not increase as unifonnly.
The difference between the
calculated pacemaker rate the normal heart rate
appeared as a triphasic response, indicating shifts in
dominance between the sympathetic and parasympathetic.
Unlike the turtle, the normal heart rate in the rat
during heating was displaced from the calculated pacemaker'
rate by overriding sympathetic activity at low and high
body temperatures (i.e., below 29 C and above 39 C) and
overriding parasympathetic activity at intermediate and
normotheric body temperatures (i.e., between 29 and 39 C).'
In the unanesthetized rat, a differential blockade
of autonomic activity with atropine and propranolol was
used to study the importance of controls on cardiovascular
responses during diving (Lin, 1970).
During diving, vagal
I
tone increased 326 per cent while sympathetic tone
decreased 48 per cent {both from predive levels).
Diving
bradycardia in mammals appears to be a combination of
decreased sympathetic tone and increased vagal tone.
I Thus,
present pharmacological determinations of autonomic
control during heating {and perhaps during diving) in
mammals reveals a more complex interaction of sympathetic
and parasympathetic components than in the turtle.
l
IL---------·
_j
_.
Central nervous control
There is some evidence for central control of
thermoregulatory responses in reptiles.
Rodbard (1950)
first introduced evidence for temperature sensitive
structures in the hypotha-lamic region of the red-eared
turtle.
\'Janning and cooling the anterior hypothalaillUS
caused a 10-20 per cent increase or decrease respectively
in blood pressure.
Hammel (1967) suggests that behavioral
thermoregulation is activated by a combination of brain
and peripheral temperatures.
Cabanac (1967) recorded
extracellular action potentials over a temperature range
of 20-36 C from the anterior hypothalamus of a lizard,
Ti~iq~
scincoides.
Heat- and cold-sensitive neurons
increased their spontaneous activity following local
heating and cooling.
The interaction of
hy~othalamic
control and autonomic
activity has been investigated more thoroughly in mammals.
Iriki {1971) measured changes in sympathetic outflow in
response to hypothalamic heating in anesthetized and
immobilized rabbits.
When the hypothalamus was heated,
activity in the sympathetic nerve to the skin was lowered
whereas visceral activity increased.
The converse effect
was obtained with cooling the hypothalamus.
The traditional concept of heart rate control suggests
that there are simultaneous reciprocal changes in activity
occurring in the two components of the autonomic nervous
73
;--~-----···-----"--------------~---------------·-······---------------,
·j
'
l
syst~~.
Epinephrine increases systolic pressure, which
!
decreases sympathetic activity while, at the srune time,
increasing· vagal discharges.
opposite effect.
Acetylcholine has just the
Yet in studies where arterial pressures
ane increased following selective pharmacological
autonomic blockade, decreases in heart rate stem from
parasympathetic mediation, withdrawal of sympathetic
activity playing no significant role.
Cardiac acceleration
resulting from decreases in arterial pressure stem from
sympathetic stimulation, parasympathetic withdrawal playing
no role (Glick and Braunwald, 1965).
The effect.s of
specific pharmacological blockade on heart rate control
suggest that the cardioregulatory centers are
' reciprocally
linked~
not
However, a more recent review
suggests ·that some degree of sympathetic-parasympathetic
interaction does occur in the central nervous system
(Higgins, et al., 1973).
Higgins,
~
al.
(1973) suggest that sympathetic-
parasympathetic interactions are modulated in the
hypothalamus.
Direct or indirect stimulation of sites
in the anterior hypothalamus induced cardiovascular
1 responses
"characteristic of parasympathetic stimuli",
II .
i whereas stimulation of centers in the posterior
I! hypothalamus
I
-
resulted in the enhancement of responses
to "sympathetic interventions and attenuation in those
I
l
to parasympathetic interventions"
L_ ____ _
L
(Higgins,
~
al.,
r··----·--·-;········----------·----~-
!
1973:128).
--·--------l
..------------·
Accordingly, the absolute decrease in heart
\
rate produced by cholinergic intervention is dependent
or,
morf~
properly, •. accentuated a in the presence of high
i
sympa·thetic stimulation to the heart.
The dose response da·ta fer- turtles indicates that
I
the higher control heart rates were followed by greater
decreases in heart rate with sympathetic blockade, whereas.
the lower control heart rates demonstrated a greater
increase in heart rate with parasympathetic blockade.
Absolute c.hanges in heart rate were greater following
parasympathetic blockade, suggesting a higher pz·eexisting
vagal tone than sympathetic tone.
Although more data for
individual turtles is needed, this suggests that an
autonomic interaction similar to mammals may exist.
1
The evidence indicates that the hypothalamus in reptiles
exercises some control over heart rate responses during
heating and cooling.
The dominant influence is vagal,
which appears to have relatively little competition from
I
·1 the sympathetic.
!
l
The cholinergic and inhibitory innervation of the
heart is characteristic of vertebrate groups.
Cardio-
accelerator fibers are also characteristic of vertebrate
evolution, although i t is at the reptile level that they
first reach the heart by separate nerve. trunks.
There is
also an overall trend in control of visceral and vascular
t. systems
j
from cholinergic to adrenergic.
L
The clear
__________j
75
effects observed in mammals is not as \<Jell-defined in
reptiles, although histochemical studies report vascular
adrenergic terminals in reptiles., (Kirby and Burnstock,
1969).
They also noted that pipero.xane produces alpha
blockade, while DCI (dichioroisoproterenol) blocks beta
receptors in Tiliqua rugosa and Bufo marinus.
is sensitive only to beta receptors.
Isoproterenol
Burnstock (1969)
suggested ·that depressor effects due to stimulation of
inhibitory receptors in the blood vessels are more
difficult to demonstrate in reptiles due to the lower
resting vasomotor tone.
Beta effects can be demonstrated
after resting tone has been increased.
Chemo- and
mechanor:eceptors found in the carotid area and retained in
1
higher vertebrates first appeared in amphibians (Burnstock,
1969).
The presence of temperature sensitive areas in the
hypothalamus, the capacity for peripheral temperature
sensitivity and vasomotor tone changes suggests that
reptiles possess an essentially complete framework for
autonomic control of cardiovascular responses.
The
thermoregulatory role of these responses becomes-more
important with the evolution of endothermy.
Successful
endothermy in mammals and birds is associated with the
i
relatively more complex central nervous system and the
i
j elaboration of peripheral temperature receptors.
L________,___
I
'
In mammals
_j
L
76
for exa.J.-nple, the hypothalamus exerts almost all its
temperature-dependent blood pressure effects through the
primary cardiovascular control center in the medulla.
Yet, as Heath (1968) points out, based on
obs'ervations that modern mammals still require large
changes (about 2 C) in bra.in temperatures to stimulate
thermoregulatory responses, there is a surprising
"reptilianu aspect to temperature sensitivity of the
hypothalamuso
Modern mammals, unlike reptiles, use
peripheral receptors to anticipate heat flux changes
in·. the body and avoid fluctuation of body temperatures,
The set points for thermoregulatory responses to heat
and cold appear to overlap in mammals, whereas they are
both distinct and dependent on ambient temperature in
reptiles {Hammel, 1965).
Heath (1968} observed that all
the properties of warm-bloodedness are found at least
incipiently in reptiles and insectso
Behavioral thermoregulation
In the preceding discussion I have suggested that
reptiles possess, in addition to an assortment of behavioral
mechanisms for thermoregulation, a complementary physiological capacity to control, to varying degrees, heat gain and
heat loss.
In many cases the thermal capacity of an
animal's environment is an indication of its capacity to
ther.moregulate.
The emydid turtles, including the genus
77
--------·--------·-1I
~---··-----~·--...- - - - - - - - - - - - - - - - - - - - · - - -
I Fse~~my~,
have the most highly developed basking habit·
of t."le Chelonia (Boyer, 1965).
Boyer suggests that the
higher temperatures associated with basking may be more
optimal for physiological processes than lower
t~nperatures
in the water.
He noted that turtles
regula·te ·their body temperature behaviorally by orienting
on basking sites so as to increase or decrease the angle
of incidence of solar radiation.
Kenyon (1925) found that peptic, tryptic and ereptic
diges·tion proceeded faster at 37 C than at room
temperature in Chrysemys and Chelydra.
The mean body
temperature of turtles (Pseudemys scripta elegans)
captured during basking was 30.2 C (Boyer, 1965).
The red-eared turtle is active at temperatures as low
; as 10 C {Boyer, 1965) while its critical thermal maxima
i (CTM) averages 41.7 C (Hutchison and Kosh, 1966).
l
Tolerances are related to activity patterns (for example,
some nocturnal reptiles tolerate and are active at lower
i body
I
.
I
! have
temperature than are diurnal ones}.
Aquatic turtles
a lower CTM than terrestrial turtles, while
i
1
semi-aquatic species are intermediate •
The Galapagos marine iguana, Arnblyrhynchus cristatus,
.1.
i
!cools only half as fast as i t heats, the greatest
I
differential yet observed in lizards (Bartholomew and
Lasiewski, 1965).
I
_j
:L_ _.
L
r-·-·--·--·-----·-··--------··--·----·---------------------------~--------~
l·
I
This unique iguana exists in a similar but more
severe thermal environment than the red-eared turtle.
! ~lyrhynchus
cristatus basks on land to preferred
tempera·ture near 37.0
c,
but to feed enters the sea
c.
which has a temperature of 22-27
Feeding takes place
underwater during dives which last 15 minutes and are
accompanied by a drop in body temperature to ambient
{Bartholomew and Lasiewski, 1965).
The basking posture
of A. cristatus is altered as the animal reaches its
preferred temperature.
Both
£·
scripta elegans and A. cristatus have
well-developed diving habits.
Voluntary diving in my
experiments was associated with a reduction in the rate
of hea·t loss during cooling.
A typical vertebrate diving
response has been shown to involve varying degrees of
i
I·
i
peripheral
1
vasoconstrictio~,
which would tend to reduce
heat loss (i.e., reduce thermal
conductance)~
The
restriction of blood flow to the periphery observed in
reptiles during cooling is a direct indication of
peripheral vasoconstriction.
Statistically, significant differences in both
heating and cooling rates have been reported for Pseudemys
floridana and other reptiles after heating and cooling
·in air and water media (Weathers,
1971).
Reflex diving
in a water medium as observed in my experiments could
i contribute to this difference, although other workers
['
L _ __ _ _ _ _ _
/
_j
79
··-'" ····-------··-----------·---------.
I'
l
----·---------~--------------
..·-------·----------,
'
have suggested that. evaporative water losses and the
.
·
l
t
specific heat of water also contribute to the disparity
(Weab~ers,
1971).
Unlike maramals, activity patterns in most reptiles
are primarily dependent on environmental temperatures ..
Marr~als,
in·turn, have a relatively well-developed
capacity for endogenous heat production and heat exchange.
I have reviewed e'tidence which suggests that reptiles
also possess to varying degrees the capacity for transient •
endogenous heat production and circulatory adjustments
for altering heat gain and heat loss.
My results
suggest that both branches of the autonomic nervous
system mediate responses of thermoregulatory significance
in the red-eared turtle.
I
l!
. '
''
i
i
'
II
\...-_,--.---~--
..-
~J
SUMMARY
Des~-
res_E9nse
1.
Atropine sulfate produces a progressive blockade
of,autonomic ganglia as well as its primary
antimuscarinic action in intravenous doses
exceeding 1 mg/kg.
2.
Propranolol and atropine decrease and increase
respectively the heart rate maximally in
intravenous doses of 1 mg/kg.
Propranolol
{1 mg/kg) also reduces the chronotropic effects
of isoproterenol (4 pg).
3.
Reductions in heart rate following sympathetic
blockade were not the resultof increased
parasympathetic
i~hibition,
in atropinized controls..
as they occurred
Consequently, it
appears that selective autonomic blockade is
not accompanied by reciprocal changes in
autonomic tone.
4.
Relative sympathetic and parasympathetic tone
appears to be related to the control heart rate.
Sympathetic and parasympathetic blockade produce
greater changes in heart rate at relatively
higher and lower control heart rate levels
i!
i
respectively.
This suggests an interaction
!_________ _
80
i
_j
81
,----·····----·--------·-----
·-.
----·---~--·----···-· --·-------~l.
which may be modulated in the central nervous
'
system.
~ating
1.
and. cooling
The normal heart rate during heating in turtles
appears to be the result of a significant and
progressively increasing vagal suppression and,
to a lesser extent, minor sympathetic augmentation.
i
2.
The similarity between the intrinsic heart rate
'
during heating and the control heart rate during
heating suggests that the latter does not
represent domination by either limb of the
autonomic nervous system (as observed in mammals).
Although subject to further experimental
verification, this suggests that the heart rate
is regulated around the temperature dependence
of the pacemaker.
3.
The differential (heart rate) between heating
heart rates and cooling heart rates, at similar
body temperatures (hysteresis of heart rate
versus body temperature) was increased with
sympathetic blockade and reduced by parasympathetic
I
I
I
blockade.
Parasympathetic fofluence was
dominant.
. I
I
l---~-
J
82
4.
Rates of heating and cooling were not consistently
or significantly related to the heart rate
changes produced by a specific drug (with the
exception of propranolol versus other drugs and
drug combinations).
This suggests that autonomic
blpckade of the heart with propranolol and
atropine does not directly affect thermoregulatory
responses.
The effects of isoproterenol and
atropine as well as information in the literature
suggest that peripheral changes (vasoconstriction
and vasodilatation) have a greater thermoregulatory
significance.
Diving bradycardia was also
associated with reduced cooling rates.
LITERATUF~
CITED
Ahlquist., R.P. (1948) A study of adrenotropic receptors.
Am,_ :1-!. Physiol. 153:586-599.
Ashley_, r..• M. (1962) Laboratory Anatomy of the Turtle.
w.c . Brown and Company, Dubuque, Iowa.
Baker, L.A. and White, F.N. (1969) Venous shunting in
the non-crocodillian reptile hearto Physiologist
12:63.
Barrett, A.M~ (1970) Pharmacology of Inderal.
1970:577-582.
Brux. Med.
Bartholomew, G .. A .. ·and Tucker, V.A. (1963) Control of
changes in body temperature, metabolism and
circulation by the agamid lizard Amphibolurus
barbatus. Physiol. Zool. 36:199-218.
Barhholornew, G.A. and Tucker, V.A. (1964) Size, body
temperature, thermal conductance, oxygen consumption,
and heart rate in Australian varanid lizards.
Phys~ol. Z_ool. 37:341-354.
Bart.holmvmew, G.A. and Lasiewski, R.C. (1956) Heating and
cooling rates, heart-rate and simulated diving in
the Galapagos marine iguana. Comp. Biochern. Physiol.
16:573-582.
Black, J.W .. , Crowther, A.F .. , Shanks, R .. G., Smith, L .. H.
and Dornhorst, A.C. (1964) New adrenergic beta
receptor antagonist. Lancet 1:1080-1081.
Boyer, D.R. (1965) Ecology of basking habit in turtles.
Ecology 46:99-108.
Burnstock, G. (1969) Evolution of the autonomic innervation
of visceral and cardiovascular system in vertebrates.
Pharmacal. Rev. 21:247-324.
Cabanac, M~, Hanunel, H.T. and Hardy, J.D. (1969) Tiliqua
scincoides: temperature sensitive units in lizard
brain. Science 158:1050-1051.
Dunlop, D. and Shanks, R.G. (1968) Selective blockade of
adrenoceptive beta receptors in the heart. Br. J.
Pharm~col. 32:201-218.
83
Gaskell, W.H. and Gadow, H. {1884) On the anatomy of
the cardiac nerves in certain cold-blmoded
vertebrates. ~· Physiol., London 5: 362-373.
Glick, G. and Braunwald, E. (1965)a
Relative roles of
the sympathetic and control of heart rate.
Circ. Res. 16:363-365.
Hammel, H.T. {1965) Nervous and temperature regulation.
In Physiological Controls (Edited by Yamamoto,. w.s.
and Brobeck, J.R.) pp. 71-98. Saunders,
Philadelphia.
Hammel, H.T. (1967) Regulation of temperature in the
blue-tongued lizard. Science 156:1260-1262.
Heath, J.E. (1968) The origins of thermoregulation.
In Evolution and Environment (Edited by Drake, E.T.)
pp. .. 259-278 •. Yale University Press, New Haven.
-
Heath, J.E., Gasdorf, E. and Northcutt, R.G. (1968)
The effect of thermal stimulation of the anterior
hypothalamus on blood pressure in the turtle.
££mp. Biochem. Physiol. 26:509-518.
Higginst C.B., Vatner, S .. F. and Braunwald, E. (1973)
Parasympathetic control of the heart. Pharmacal.
Rev. 25:119-155.
Hutchison, V.H., Vinegar, A. and Kosh, R.J. (1966)
Critical thermal maxima in turtles. Herpetologica
22:32-41.
Innes, I.R. and Nickerson, M. (1970) Drugs inhibiting
the action of acetylcholine on structures innervated
by postganglionic parasympathetic nerves
(antimuscarinic or atropinic drugs). In The
Pharmacological Basis of Therapeutics (Ed~ted by
Goodman, L.S. and G~lman, A.) pp. 524-548.
Macmillan Company, New York.
Iriki, M., Riedel, w. and Simon, E. (1971) Regional
differentiation of sympathetic activity during
hypothalamic heating and cooling in anesthetized
rabbits. Pfluegers Arch. 328:320-331.
Jackson, D.C. and Schmidt-Nielsen, K. (1965) Heat
· production during diving in the fresh-water turtle,
Pseudemys scripta. J. Cell Physiol. 67:225-232.
85
Jose, A.D. {1966) Effect of combined sympathetic and
parasympathetic blockade on heart rate and cardiac
function in man. Am. J. Cardiel. 18:476-478o
Jose, A.D. and Stitt, F. (1967} Cardiac function after
combined beta-adrenergic and cholinergic blockade.
Circ. Res. 20-21:11/231-11/242.
Jose, A.De and Stitt, F .. · (1969) Effects of hypoxia and
metabolic inhibitors on the intrinsic heart rate
and myocardial contractility in dogs. Circ. Res.
25:53-66.
Josa, A.D .. and Taylor, R.R. (1969) Autonomic blockade
by propranolol and atropine to study intrinsic
myocardial function in man. J. Clin. Invest.
48:2019-2031.
Jose, A.D., Stitt, F. and Collison, D. (1970) The effect
of exercise and changes in body temperature on the
intrinsic heart rate in man. Arn.Heart J. 79:
488-498.
Jose,
A~D. and Collison, D.
(1970) The normal range and
deterrn1nants of the intrinsic heart rate in man.
Cardiovasc. Res. 4:160-167.
Kaplan, H.M. (1957) The care and diseases of laboratory
turtles. Animal Care Panel Proc. 7:259-272.
Kaplan, H.M. (1969) Anesthesia in amphibians and reptiles.
Fed. Proc. 28:1541-1546.
Kenyon, W.A. {1925) Digestive enzymes in poikilothermal
vertebrates, and investigation of enzymes in fishes
with comparative studies of those in amphibians,
reptiles and mammals. Bull. u.s. Fish. 41:179-200.
Kirby, s. and Burnstock, G. (1969) Pharmacological studies
of cardiovascular system of the sleepy lizard
(Tiliqua rugosa) and Bufo marinus. Comp. Biochem.
Physiol. 28:321-331. ----Ledsome, J.R., Linden, R.J. and Norman, J. (1965) The use
of sympathetic beta-receptor blocking agents in the
investigation of reflex changes in heart rate.
Br. J. Pharmacal. 24:781-788.
Lin, Y. (1972) Autonomic nervous control on the
cardiovascular response of unanesthetized rats
during diving. Fed. Proc. 31:368.
Maickel§ R~P~ (1970) Interaction of drugs with autonomic
nervous function and thermoregulation. Fed. ·Proc.
29:1973-1979.
Martin, H .. N. and Moale, W.A. (1881) How to Dissect a
Chelonian: Handbook of Vertebrate Dissection ..
Vol. 1, Macmillan Company, New York.
Meyers, F.H., Jawetz, Es and Goldfien, A. (1970) Review
of Medical Pharmacology. Lange Medical Publ~cations,
Los Altos, California.
Morgareidge, K.R. and White, F.N. (1969a) Cutaneous
vascular changes during heating and cooling in
the Galapagos marine iguana. Nature 223:587-591.
Morgareidge, K.R. and \ihite, F.N. (1969b) Nature of heat
induced cutaneous vascular response in Iguana iguana.
Rodbard, s. (1950) Thermosensitivity of the turtle brain
as manifested by blood pressure changes. Am. J.
~Eysiol. 160:402-408.
Shanks, RoG. (1966a) The pharmacology of beta sympathetic
blockade. Am. J. Cardiel. 18:308-316.
Shanks, ReG. (1966b) The effects of propranolol on the
cardiovascular responses to isoprenaline, adrenaline
and noradrenaline in the anesthetized dog. Br. J.
Pharmacal. 26:322-333.
Shanks, R.G. (1967) The peripheral vascular effects of
propranolol and related compounds. Br. J. Pharmacol.
29:204-217.
Spray, D.C. and Belkin, D.B. (1973) Thermal patterns in
the heating and cooling of Iauana iguana and Ctenosaura
hemilopha. Comp. Biochem. Physiol. 44A;881-892.
Spray, D.C. and Belkin, D.B. (1972) Heart rate-cloacal
temperature hysteresis in Iguana is a result of
thermal lag. Nature 239:337-338.
Spray, D.C. and May, M.L. (1972) Heating and cooling rates
in four species of turtles. Camp. Biochem. Physiol.
41A:507-522.
Tucker, V.A. (1966) Oxygen transport by the circulatory
system of the green iguana (Iguana iguana) at
different body temperatures. J. Exp. B~ol. 44:77-92.
87
Walsh, R.R. (1969) Heart rate and its neural regulation
with rising temperature in anesthetized ra·ts •
.Am. J .. Phys.iol. 217:1139-1143.
Weathers, w.w., Baker, L.A. and White, F.N. (1970)
Regional ~edistribution of blood flow in lizards
during heating$ ~hxsiologist 13:336.
Wea·thers, w.w. and Morgareidge, K.R. (1971) Cutaneous
vascular responses to temperature change in the
spiny-tailed iguana, Ctenosaur~ hemilopha. Copeia
1971:548-551.
Weathers, w.w. (1971) Some cardiovascular aspects of
· temperature regulation in the lizard Dipsosaurus
dorsalis. Comp. Biochem. Physio1. 40A:505-515.
Weathers,
w.w.
-
.
and t'Vhite, F .. N. (1971) Physiological
in turtles. Am. J. Physiol.
221:704-710.
b~ermoregulation
White, F.N. and Ross, F. (1966) Circulatory changes
during experimental diving in the turtle. Am. J.
Physiol. 211:15-18.
Wilson., J .. A .. (1972) Principles·of Animal Physiolog:r:.
Macmillan Compa.ny, New York.
Wilson, K.J. and Lee, A.K. (1970) Changes in oxygen
consumption and heart rate with activity and body
temperature in tuatara, (Sphenodon punctatum).
Comp. Biochem. Physiol. 33:311-322.