Cardiac sympathetic nerve activity and heart
rate during coronary occlusion in awake cats
ISHIO
NAOKI
NINOMIYA,
NISHIURA,
KANJI
MATSUKAWA,
TOSHIHIRO
AND MIKIYASU
SHIRAI
Department
of Cardiac Physiology,
Suita, Osaka, 565 Japan
National
Cardiovascular
Center Research
Institute,
mals (3, 6, 7, lo), but in all of those studies, no detailed
analyses of their relationship
to HR modulation
were
made. We considered the possibility that anesthesia directly influences not only the pacemaker cells but also
the vagal and sympathetic nervous system, and in turn,
modifies the relationship
of neural signals to HR responses. It was desirable to conduct the occlusion experiment in unanesthetized, conscious animals, because information about responses in efferent cardiac sympathetic and/or cardiac vagal nerve activities to coronary
occlusion was lacking.
The purpose of this study was I) to supply information
about responses in efferent cardiac sympathetic nerve
activity (CSNA) and HR due to anterior descending
coronary occlusion in both conscious and anesthetized
cats, and 2) to determine the contribution of sympathetic
and vagal nerve activities on HR changes during coronary occlusion.
cats. Am. J. Physiol. 251 (Heart Circ. Physiol. 20): H528-H537,
1986.-Responsesin efferent cardiac sympathetic nerve activity (CSNA) and heart rate (HR) to a 100-santerior descending
coronary artery occlusionwere measuredin cats under awake,
atropinized, anesthetized, or anesthetized and atropinized
states.In the consciousstate, at 20 and 90 s of occlusion,CSNA
increased by 23% and then decreasedby 7%, respectively,
whereasHR decreasedby 5 and 17%, respectively. With atropinization and/or anesthesia,the initial increasein CSNA was
inhibited and the later decrease in CSNA was enhanced,
whereasthe bradycardia was diminished. HR changedin proportion to CSNA responseswith high correlations, i.e., r =
+0.89, +0.90, +0.96, and -to.91 for the four states, respectively.
In the conscious state, the CSNA-HR relation line shifted
toward bradycardia, but this shift wasblocked by atropinization
and anesthesia.This finding suggestedthat, in the conscious
state, cardiac vagal nerve activity (CVNA) increasedimmediately and did not decreaseduring occlusion. At the early stage
of occlusion, HR response (bradycardia or tachycardia) was METHODS
determinedby the relative contribution of enhancedCSNA and
CVNA. At the later stage of occlusion, bradycardia wasinduced Preparation of Animals
by a combination of decreasedCSNA and enhancedCVNA. In
The experiments were carried out on 19 cats (1.8-4.2
anesthesiaand/or atropinization it was induced mainly by the
kg
body wt). They were anesthetized with pentobarbital
decreasedCSNA.
consciousand anesthetized cats
on cardiac rhythm,
infarction, have been extensively studied in human subjects and in animals (5).
During acute experimental
coronary occlusion, either
increase, no change, or decrease in heart rate (HR) was
reported in anesthetized cats (4, 7, 22) and dogs (6) and
in unanesthetized
dogs (15, 16, 18) and monkeys (17).
However, little is known about the neural mechanism
that causes the change in HR during occlusion in the
conscious cat.
To analyze autonomic neural mechanisms responsible
for bradycardia, no change, or tachycardia during coronary occlusion, it is important
to directly record the
efferent sympathetic and/or vagal nerve activities of the
pacemaker region together with the HR. The efferent
sympathetic post- and preganglionic nerve activities were
recorded during coronary occlusion in anesthetized aniAUTONOMIC
NEURAL
INFLUENCES
resulting from myocardial
H528
0363-6135/86 $1.50 Copyright
sodium (30-35 mg/kg ip) for surgical implantation
of
recording electrodes and catheters. Each cat was intubated with an endotracheal tube and artificially
ventilated with room air. Muscle movements were prevented
with pancuronium
bromide (0.7 mg/kg im) throughout
the implantation,
and then an antibiotic was given.
Implarttation of Recording Electrodes
and Coronav Occluder
Under aseptic conditions, a left thoracotomy was made
in the 4th intercostal space. Using a dissecting microscope (Olympus OME) a branch of the left inferior
cardiac sympathetic nerve, which innervated mainly to
the left side of the heart, was separated ml-l.5 cm in
length, near the aortic arch, from the surrounding connective tissue (Fig. 1, left panel). The nerve bundle (-1
cm in length) was carefully desheathed at the site of the
recording electrode implantation.
The details of the size
and configuration of the implantable electrode assembly,
which consists of collagen and reference electrodes, have
been described previously (14). After the nerve bundle
0 1986 the American
Physiological
Society
Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on September 18, 2016
NINOMIYA, ISHIO, KANJI MATSUKAWA, TOSHIHIRO HONDA,
NAOKI NISHIURA, AND MIKIYASU SHIRAI. Cardiuc sympathetic
nerve activity and heart rate durirtg coronary occlusion in awake
HONDA,
CARDIAC
SYMPATHETIC
ACTIVITY
Experimental
Measurements
While the animal was conscious, the original neurogram of the cardiac sympathetic
nerve (NS) and bioelectrical noise signal (BEN) were measured simultaneously
from the collagen and reference electrodes of the implanted assembly,
respectively.
The signals from the
electrodes were amplified by biophysical
preamplifiers
(Nihon Kohden, AVB-8) with a high cut-off frequency
CORONARY
OCCLUSION
H529
of 3,000 Hz and a low cut-off frequency of 50 Hz; the
signals were monitored with a two-channel
storage oscilloscope (Hitachi,
V 6051). By comparing the NS and
BEN signals, the original CSNA was separated and
displayed on a dual-beam storage oscilloscope (Tektronix
5113) (Fig. 1, right panel). The original CSNA was converted into standard pulse trains using a modified digital
technique of Wiemer et al. (24), which detected the peaks
of the original neural waves. Then the standard pulse
trains were integrated continuously
with a resistancecapacitance integrator having a time constant of 20 ms.
The integrated standard pulse signal was called CSNA,
and the amplitude was shown by impulses per second
(imp/s).
Mean cardiac
sympathetic
nerve activity
(MCSNA)
was obtained by smoothing the CSNA with a
resistance-capacitance
integrator having a time constant
of 1 s. The CSNA (or MCSNA)
was averaged over a
period of 10 s and denoted as CSNA. In all cats, the
CSNA and the epicardial ECG were measured simultaneously. The instantaneous
HR was obtained from the
inverse value of the R-R interval of the ECG by using
an HR meter (25). The arterial blood pressure (AP) and
its mean value (MAP) were measured with a pressure
transducer
(Gould P50 or Statham P23De) attached to
the end of the catheter in the left common carotid artery.
The NS, BEN, original CSNA, CSNA, ECG, AP, and
HR were stored continuously
on a seven-channel
magnetic tape recorder
(TEAC,
SR-31).
The CSNA,
MCSNA,
ECG, HR, AP, and MAP were displayed on a
heat -pen polygraph (Sanei).
Experimental
Protocol
and Data Analyses
The “noise” level of the recording system and of the
CSNA was determined as follows. Before implanting the
recording electrodes, we placed them in a physiological
saline solution and measured the peak to bottom “electrical noise” (in pV) of our recording system, including
the electrodes. After implantation,
to detect the CSNA
signals, we carefully monitored discharge patterns of the
original CSNA on the oscilloscope, and selected the most
adequate threshold value, which was an approximately
540% larger amplitude than the electrical noise. Only
when the original CSNA signal (in pV) exceeded the
presetting threshold value was it converted sequentially
into a train of standard pulses. During the experiments,
we used a hexamethonium
bromide (3 mg/kg iv) for
FIG. 1. Locations
of occluder,
implantable
electrodes for recording
cardiac sympathetic
nerve activity
(CSNA),
and bioelectrical
noise, and ECG electrode
are shown schematically.
Shown are high-speed
data
of an electrocardiogram
(EGG),
original
CSNA
and
CSNA
recorded
in an awake cat who is in a quiet
reclining
posture on 2nd day after surgical implantation. Grouped
discharges
in original CSNA and CSNA
synchronous
with cardiac cycle could be seen. LAD,
left anterior
descending
coronary
artery;
LA, left
atrium;
LV, left ventricle;
PV, pulmonary
vein.
ELECTRODE
Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on September 18, 2016
was placed on the collagen electrodes in the channel
through the slit of the implantable electrode assembly,
the slit was completely closed with sutures. The assembly
was then sutured to the surrounding
connective tissue
near the aortic arch. The lead cables, consisting
of a
recording
electrode
and a reference
electrode,
were
brought to the body surface and connected with a socket
that was firmly attached to the back side of the animal.
In all cats, the pericardium
was incised parallel to the
left phrenic nerve, and the edges were suspended to the
chest wall to make a pericardium cradle. The left anterior
descending (LAD) coronary
artery was chosen in this
study, because it is technically the easiest coronary vessel
to occlude. With the aid of the dissecting microscope, an
inflatable occluder was attached to the LAD coronary
artery near the circumflex artery with special care taken
to prevent damage to the pericoronary
nerve (20) and to
ensure that the vessel was unobstructed
when the occluder was deflated. A small tube (PE-10) connected to the
occluder was brought out to the body surface in the
intrascapular
region of the animal’s back. During the
experiment,
normal
heparinized
saline was injected
through this small tube and inflated the balloon for
occlusion of the coronary vessels.
An ECG electrode (Teflon-coated
stainless steel wire,
0.003 in., Medwire)
was implanted directly on the left
ventricular surface of the LAD coronary distribution
area
to monitor
myocardial
electrical
activity
(epicardial
ECG) in the ischemic region during LAD coronary occlusion. A ground electrode (silver-plated,
8 x 8 mm) was
implanted in the back of the right shoulder. Lead wires
from the ECG and ground electrodes were fixed on the
socket in the intrascapular
region. Heparin -filled catheters (ID = 0.9; L, 250 mm) were inserted into the left
jugular vein for infusion of drugs and into the left common carotid artery for recording the arterial blood pressure,
TO
H530
CARDIAC
SYMPATHETIC
ACTIVITY
CORONARY
OCCLUSION
served a spontaneous
variation of CSNA and HR in
awake cats (12). It is desirable to estimate the variability
of the CSNA and HR during the preocclusion period. In
each trial, a ground mean value of CSNA and of HR
measured at 10 different periods in the 100-s preocclusion, was defined as cCSNA and cHR, respectively. Relative changes (%) of CSNA (ACSNA) from the cCSNA
and of HR (AHR) from the cHR were sequentially obtained in each of 10 periods. In the same manner, ACSNA
and AHR were obtained at 10 periods during 100-s occlusion, In the figures and in the results we report the means
& SE and number of experimental
trials.
In each state, the significance of responses against
preocclusion variations were evaluated by the one-way
analysis of variance ( 19). Least -squares linear regression
analysis of AHR to ACSNA were made in the four states,
and they were compared with each other by analysis of
covariance (19). The level of significance was 0.05 in all
cases.
RESULTS
Awake State
Origin of cardiac sympathetic nerve activity and its
discharge pattern at the preocclusion control. In all 16
awake cats, we measured a “pure” cardiac sympathetic
nerve activity. This was confirmed by preliminary experiments that showed that when the left vagal nerve trunk
at the cervical level was stimulated electrically, no action
potential was evoked in the CSNA.
Grouped discharges synchronous with the cardiac cycle
and its respiratory modulation were frequently observed
in the CSNA (e.g., Figs. 1 and 2A). As shown in Fig. 2B,
with administration
of a ganglion blocker (hexamethonium bromide, 3 mg/kg iv), the grouped CSNA synchronous with the cardiac cycle and respiration disappeared
and decreased near the noise level. AP fell while heart
rate decreased. We examined the possibility of afferent
CSNA from the occluded area. Under the ganglion
blocker, no detectable changes in the CSNA were produced with occlusion. With administration
of norepinephrine (2 pg/kg iv), the CSNA was inhibited near the
noise level associated with hypertension. These findings
showed that the major parts of the CSNA recorded
during preocclusion in the reclining conscious cats were
the postganglionic
sympathetic fiber activity and baroceptor reflex-dependent
components, as were those in
the anesthetized state (9). Afferent activity from the
ischemic area was not contained in the CSNA during
occlusion.
Responsepatterns in cardiac sympathetic nerve activity,
heart rate, and arterial pressure to occlusion. Figure 3
shows a typical example of a complex pattern of responses in MCSNA and HR, together with MAP and AP
at the first trial of occlusion. Immediately
after onset of
occlusion, bradyarrhythmia
occurred following the fall
in AP, whereas MCSNA remained unchanged (Fig. 3,
open arrow). At 12 s after occlusion, the animal seemed
excited and moved its body. MCSNA increased significantly, as shown by the solid arrow, and tachyarrhythmia
resulted. Such sudden large increases in MCSNA, asso-
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determining
the “noise” level of the postganglionic
sympathetic nerve activity.
To examine whether the left inferior cardiac sympathetic nerve contains the efferent and afferent vagal
fibers, we electrically
stimulated
the left vagal nerve
trunk at the cervical level with rectangular pulses (intensity, 8 V; pulse width, 1 ms) by an electronic stimulator
(Nihon Kohden, SEN 7103) in anesthetized conditions.
No action potential was evoked in the CSNA. The left
inferior cardiac nerve corresponding to the stellate cardisc nerve (1) contain .ed no vagal fibers.
In open-chest conditions, we tested the occluder and
examined changes in the configuration
of the epicardial
ECG during a complete occlusion. Amplitudes
of the
QRS spikes and of the T-wave changed, and the ST
segments shifted significantly,
accompanied by changes
of color in the occluded area. Only when such specific
changes in the epicardial ECG were observed during
occlusion in the awake state did we consider our occlusion system to be good. We confirmed ‘that a complete
occlusion was produced in each of the 19 cats. Therefore,
we used all 19 in the short-duration
occlusion (100-s)
experiments conducted in the four different states, i.e.,
awake, awake plus atropine, anesthesia, and anesthesia
plus atropine.
The complete occlusion data, that we judged by using
the specific changes in the epicardial ECG, were sampled
mostly in 2-4 days (average, 2.6 days) after implantation
surgery in 16 of the 19 cats which were drinking milk,
eating, sitting, and standing spontaneously during p reocelusion control periods. In a given experimental
day 9
short-duration
occlusions were made when the animals
were in a quiet reclining or sitting posture before the
occlusion of the coronary artery. A good record was
technically difficult to obtain at the first trial. Many data
for statistical analyses were sampled after the second
trial of occlusion, which was repeated after stabilization;
this was assured by relatively constant mean levels of
CSNA and HR, and by recovery of the waveforms of the
epicardial ECG.
In 7 of 16 cats, after the occlusion experiments in the
awake sltate, atropine sulfate (0 1- -0.2 mg/kg) was administered intravenously,
and then the occlusion experiments were repeated within 30 min.
In 14 of 16 cats, the occlusion experiments were repeated under anes t hesia. We h ave observed that a deep
anesthesia due to a one -shot intravenous injection of
pentobarbital
sodium ( 30 mg/kg) caused many disturbantes such as cessation or significant inhibitions of spontaneous respiration, inhibitions
of CSNA, and a fall in
AP. To avoid these disturbances, we initially
administered pentobarbital
sodium (15 mg/kg iv), and then carefully added 5 mg/kg sequentially, which led into a light
anesthesia. Total doses of 20-25 mg/kg iv adequately
blocked pain responses and led to a complete loss of
consciousness during the short-duration
occlusion experiments.
In 4 of 14 anesthetized cats, atropine sulfate (0.1-0.2
mg/kg iv) was administered,
and then the occlusion
experiments were repeated.
As reported previously from our laboratory, we ob-
TO
CARDIAC
SYMPATHETIC
ACTIVITY
TO
A CONTROL
CORONARY
6
OCCLUSION
HEXAMETHONIUM
H531
BROMIDE
AP
mmHg
CSNA
imp/s
ECG
FIG. 2. Arterial
pressure
(AP), cardiac sympathetic
nerve activity
(CSNA),
and ECG measured
before (A) and
after (B) intravenous
administration
of hexamethonium
bromide
(3 mg/kg)
in awake state are shown. With hexamethonium
bromide,
CSNA synchronous
with cardiac cycle disappeared
and decreased near the noise level while AP and
heart rate decreased.
LAD
OCCLUSION
OFF
ON
4
MCSNA
imp/s
HR
beats/m
180-,
l
III’/
I I I I
rn-r
MAP
mmHg
AP
mmHg
FIG. 3. Influences
of occlusion
of the left descending
coronary
artery
(LAU)
on mean cardiac sympathetic
nerve
activity
(MCSNA),
heart rate (HR), mean arterial
pressure (MAP),
and arterial pressure
(AP) in awake state obtained
on 2nd day after surgical implantation
are shown. Significant
hypotension,
changes in MCSNA
and HR can be seen.
Bradyarrhythmia
is observed
immediately
after onset of occlusion
(open arrow).
Large increase in CSNA (solid arrow)
produced
transient
tachyarrhythmia
(solid arrow)
associated
with excitement.
ciated with excitement and followed by a transient tachycardia, occurred in 43% (3) of the first 7 trials and in
13% (4) of 31 repeated trials at the early stage of occlusion. At 40-100 s of occlusion the animals were in a quiet
reclining posture that was accompanied by bradycardia,
hypotension,
inhibition
of MCSNA,
and increased respiratory frequency.
Time courses and magnitudes of responses in cardiac
sympathetic nerve activity and heart rate. A typical example of HR and CSNA responses in repeated trials of
occlusion before and after atropine is shown in Fig. 4, A
and B, respectively. In Fig. 4A, in a 30-s occlusion,
MCSNA remained almost the same. At 30-90 s of occlusion, MCSNA tended to decrease. On the other hand,
cardiac slowing occurred in two phases; an early fast
response and a later slow response. The early phase of
bradycardia was observed in 15 of 38 trials (7 of 16 cats),
whereas the later slow response was observed in 32 of 38
trials (14 of 16 cats). The early bradycardia was abolished
after administration of atropine (Fig. 4B).
Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on September 18, 2016
mV
H532
CARDIAC
SYMPATHETIC
ACTIVITY
TO CORONARY
OCCLUSION
ATROPI
L
The variations and responses of CSNA (ACSNA) from
the cCSNA were obtained sequentially at 10 periods in
100-s preocclusion and at 10 periods during 100-s occlusion, respectively (Fig. 5, upper panel, solid circles). In
each period, the mean value and SE was obtained from
38 experimental
trials. Before occlusion, the variations
of CSNA ranged from +2% to -2%. During the 100-s
occlusion, CSNA response increased to the peak value of
23% at 20 s and then decreased to the lowest value of
-7% at 90 s after the onset of occlusion. In the conscious
cats, the cHR was 164 t 5.4 (n = 38) beats/min. The
variations of HR at the preocclusion periods were less
I I
NE
FIG. 5. Percentage changes of cardiac
sympathetic nervous activity (m)
from the control CSNA (cCSNA) and of
average heart rate (HR) from the control
HR (cHR) at 20 periods obtained before
and during 100 s of coronary occlusion
in the conscious state are shown in upper
and lower panels, respectively. In each
period, mean k SE was obtained from 38
experimental trials before (control: sold
circles) and from 9 experimental trials
after atropinization (atropine: open circles). Asterisks
indicate a significant
change of ACSNA from variations in
preocclusion (P < 0.05).
than 1% (Fig. 5, lower panel, solid circles). With occlusion, HR decreased immediately
and progressively to the
lowest value of -17% less than the cHR at 90 s of
occlusion. These findings indicate that I) in the early
stage of occlusion, the CSNA increases above the preocelusion control level, whereas the HR decreases; 2) during
the late stage of occlusion, the CSNA returns to the
control level and even decreases while the HR continues
to decrease even more.
To analvze a comPlex relationshiP
between the responses inlCSNA ana HR during ocElusion (Fig. 5) the
mean values of AHR were plotted as a function of that
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FIG. 4. Responses in heart rate (HR) and mean cardiac sympathetic nerve activity (MCSNA) to left anterior
descending (LAD) coronary occlusion before (A) and after (B) atropinization
(0.1 mg/kg iv) are shown. With
atropinization, the control HR increased significantly, but MCSNA remained almost constant. Bradycardia at early
stage of occlusion seen in A was blocked in B, bradycardia at late stage of occlusion was not. Relative contributions
of vagal (solid arrows) and sympathetic (open arrows) during occlusion are schematically shown.
CARDIAC
SYMPATHETIC
ACTIVITY
TO
CORONARY
OCCLUSION
H533
of ACSNA in Fig. 6A, solid circles, and a least-squares
linear regression analysis was applied (19). A high positive correlation between two variables, i.e., r = +O.89,
suggests that HR changed in proportion to the changes
in CSNA during the 100-s occlusion. The slope, i.e.,
regression coefficient, of the fitted line is +0.4 (P <
O.OOl), meaning that the HR changes on the average by
40% for each 100% change in the CSNA during the 100s occlusion. A significant negative intercept value (P <
0.01) of the regression equation, i.e., -12.8%, suggests
that factors other than CSNA operate independently and
shift the CSNA-HR
relation line toward bradycardia
(-21 beats/min)
during occlusion.
bradycardia, as was observed in the control experiment.
A small but significant positive regression coefficient (P
< 0.001) and a high positive correlation coefficient (0.90)
indicates that during occlusion, when the influence of
CVNA was blocked, the decrease in HR was produced by
the decreased CSNA.
To examine whether or not the difference in the linear
regressions between the control and atropinization
are
significant,
we compared the residual variances first,
then the slopes, and then the shifts of the intercept
values with bradycardia (19). The residual mean squares
show signs of a real difference. The slope and intercept
values were decreased by atropine in the awake state.
Effect of Atropinization
Effect of Anesthesia
in the Awake State
A
In anesthetized and closed-chest conditions, changes
of CSNA (or MCSNA) and HR in response to acute
LAD coronary occlusion were recorded from 22 experimental trials. An example of the slow-speed data obtained in the conscious (A) and anesthetized (B) state is
shown in Fig. 7. It was observed that at the preocclusion
control period, respiratory modulation
in MCSNA was
more significant in the anesthetized state (B) than in the
conscious state (A), but MCSNA tended to decrease.
With anesthesia, the cCSNA was not increased, but the
cHR increased to 175 t 7 beats/min
(n = 22). These
findings indicate that the increased HR with anesthesia
was not produced by augmented CSNA.
During LAD coronary occlusion, as shown in Fig. 7,
CSNA and HR changed with different time courses in
the two states. In the conscious state, bradycardia occurred immediately
after the onset of occlusion, but
disappeared with anesthesia. At 8 s after occlusion,
MCSNA increased suddenly, as indicated by the star,
but it disappeared with anesthesia. A similar analysis to
that done in the awake state was made of the anesthetized state as shown in Fig. 8, solid circles. The variations
in CSNA and HR at the preocclusion were small in
anesthesia. In the early portion of the occlusion, responses in CSNA and HR were not statistically significant, except for those in CSNA at 10 s. During the late
stage of the occlusion, CSNA and HR decreased gradually below the control level, and they reached a low of
B
%CHANGE
IN
CSNA
%CliANGE
FIG. 6. Mean values of responses in cardiac sympathetic nerve activity (CSNA) and heart rate (HR)
in Fig. 5 are used to analyze an interreIationship
between ACSNA and AHR during a 100 s left anterior
descending coronary artery (LAD) occlusion. Percentage change in HR is expressed as a function of that in
CSNA. Diagonal solid lines are linear regression lines.
Inner pairs of dashed curues are 95% confidence zones
of regression lines. Outer pairs of dotted curves are
95% confidence zones of sampled data. In conscious
state (A), regression equation (%) and correlation
coefficient is y = 0.4 x: - 12.6 and r = +0.89, respectively.
SD of sampled data from regression is 1.2%.
With atropinization (B), regression equation (%) and
correlation coefficient are y = 0.2 x - 1.4 and r =
+0.90, respectively. SD from regression is 1.5%. Difference of 2 regression lines is significant.
IN
CSNA
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With atropinization,
the cHR at the preocclusion periods increased significantly to 203 -+ 6.9 (n = 9) beats/
min, due to blocking the effect of cardiac vagal nerve
activity on the pacemaker cells. Relative responses in
CSNA and HR to occlusion obtained from nine trials are
summarized
in Fig. 5 by open circles. At lo-50 s of
occlusion, CSNA remained almost constant, whereas HR
tended to decrease. During the late stage of occlusion,
i.e., 60400 s, both CSNA and HR decreased progressively and reached -32% and -8%, respectively, during
the 90-s period of occlusion. The decreases in CSNA and
HR at 90 s were statistically
significant compared with
those in the control state. The results shown in Fig. 5
obtained before (solid circles) and after atropinization
(open circles), indicate that in the early stage of the
occlusion, the increase in CSNA, and the decrease in HR
were abolished by atropine. On the other hand, in the
late stage of the occlusion, the decreases in CSNA were
rather enhanced by atropine, whereas the decreases in
HR were diminished by atropine.
The effects of atropine on the CSNA-HR
relationship
during 100 s of occlusion were investigated. In Fig. 6B
the relationship
of AHR to ACSNA in each of the 10
occlusion periods in Fig. 5 (open circles) was plotted, and
a least-squares regression analysis was applied. There
was a high positive correlation between the two variables,
i.e., r = +0.90. A small and a no significant intercept
value showed that the fitted line did not shift toward
H534
CARDIAC
SYMPATHETIC
LAD
A
ACTIVITY
TO
CORONARY
6
OCCLUSION
I
%;sA
OCCLUSION
LAD
I
I .
*
OCCLUSION
120.
OI
k$zNA
60-
HR
beats/m200:
120.
10 set
10 set
FIG.
7. Slow-speed
data showing
(from top to bottom)
cardiac sympathetic
nerve activity
(CSNA),
mean CSNA
(MCSNA),
and heart rate (HR) before and during left anterior
descending
coronary
(LAD) occlusion
in a cat in awake
(Al
(B) state. Note different
time courses and magnitudes
of response curves in MCSNA
and HR to
\- , and anesthetized
occlusion
between 2 states.
OCCLUSION
Y
F
’ -s’o ’ -$o
’ -a,
’ -;o
’
;,
’ $0 ’ a,
’
$0 ’ E&J ’ l&3 SEC
FIG. 8. Shown
are means ? SE of
change in cardiac sympathetic
nerve activity
(ACSNA)
and of change in heart
rate (AHR) obtained
at 20 periods before
and during
occlusion
under anesthesia.
In each period
ACSNA
and AHR are
obtained
from 22 and 4 experiments
before (control:
closed circles)
and after
atropinization
(atropine:
open circles),
Asterisks denote a signifirespectively.
cant difference
in CSNA response to occlusion
from variation
in preocclusion
periods (P < 0.05).
h 2o
M
u
“IO
-a
-20
--- -- -f .
~*=======----Q%$~*~
L
t-- * ._ -- -- -_
t
*
-18 and -14%, respectively, at 90 s of the occlusion.
The mean values of ACSNA and AHR obtained at 10
periods during occlusion in Fig. 8 were used to analyze
their relationship and were plotted in Fig. 9. There was
a good positive correlation between the two variables,
i.e., r = +0.96. The positive slope of the fitted line is 0.6
(P < O.OOl), meaning that the HR changes on the average
by 60% for each 100% change in the CSNA during a lOOs occlusion. A small negative and no significant intercept
value indicated that the CSNA-HR relationship tends to
shift toward bradycardia, but not significantly. With
LAD coronary occlusion in the anesthetized cats the HR
decreasewas mainly dependent on the decrease in CSNA.
Effect of Atropinization
Under Anesthesia
With atropinization in the anesthetized state, the cHR
was 183 f 3 (n = 4), whereas that of cCSNA remained
almost constant. In Fig. 8, mean values of CSNA and
HR responses obtained during occlusion are shown by
open circles. Responses in CSNA and HR remained the
same in the early 30-s occlusion period, but after the 40s occlusion they decreased progressively below the preocelusion level and reached -19 and -12%, respectively,
at the 90-s occlusion. No significant differences in CSNA
and HR responses between control and atropine were
found.
Using the mean values of ACSNA and AHR at 10
periods in Fig. 8, the CSNA-HR relationship during
occlusion in the atropinized and anesthetized states were
examined in Fig. 9B. There was a good positive correlation between the two variables, i.e., r = +0.91. A positive
slope (P < 0.001) and a small intercept value of the linear
regression line showed that with atropinization in anesthetized cats the decrease in HR by occlusion was in-
Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on September 18, 2016
160-
CARDIAC
SYMPATHETIC
ACTIVITY
TO
CORONARY
1
0
O/o CHANGE
IN CSNA
o/o CHANGE
IN
DISCUSSION
In this study we investigated the response patterns of
efferent CSNA and HR to a 100-s occlusion of the LAD
coronary artery in both conscious and anesthetized cats,
with and without
atropinization,
and we attempted to
estimate a relative contribution
of CSNA and of efferent
cardiac vagal nerve activity (CVNA) on HR modulation
during occlusion.
We found that responses in CSNA, CVNA, and HR to
LAD coronary occlusion differed significantly
between
the two states. In the conscious state as compared with
the anesthetized state, the CSNA and CVNA increased
simultaneously
at the early stage of occlusion, and HR
response (tachycardia
or bradycardia)
was determined
by a relative contribution
of enhanced CSNA and of
enhanced CVNA. The CSNA decreased reciprocally with
the increased CVNA at the later stage of occlusion, and
bradycardia
was induced by a combination
of decreased
CSNA and enhanced CVNA. On the other hand, in the
anesthetized
state, similar to the atropinized
state, the
HR was determined
mainly by changes in the CSNA.
We observed that when the large increase in CSNA
associated with emotions and/or body movements
occurred at the time of enhanced CVNA, a transient tachyarrhythmia
was induced. The importance
of simultaneous activation of CSNA and CVNA on the arrhythmia
during coronary occlusion was suggested previously
(7,
23) .
Limitations
Differences
elusion HR
anesthetized
tained under
191-199 (8),
and Assumptions
due to experimental conditions. The preoc(cHR)
differed significantly
between the
and awake animals. The cHR in cats, obdifferent anesthesia, was 196 (4), 196 (7),
239 (ZZ), and 175 beats/min
(in this study).
H535
FIG. 9. Mean
values of percentage
responses
of
average
cardiac sympathetic
nerve activity
(m)
and average heart rate (m)
in Fig. 8 are used in this
figure
for analysis
of an interrelationship
between
ACSNA
and AHR during
occlusion.
Diagonal
solid
lines are least squares linear regression
lines. Inner
pairs of dashed curves are 95% confidence
zones of
regression
lines. Outer pairs of dotted curves are 95%
confidence
zones of sampled
data. In anesthetized
state (A), regression
equation
(%) and correlation
coefficient
are y = 0.6 x - 4.1 and r = +0.96, respectively.
SD of sampled data from regression
is 1.4%.
With atropinization
under anesthesia
(B), regression
equation
(%) and correlation
coefficient
is y = 0.5 x 1.0 and r = +0.91, respectively.
SD from regression
is
2.1%. Difference
of 2 regression
lines is not significant.
CSNA
The cHR in the awake state (164 beats/min in this study)
was significantly
lower than that in the anesthetized
state, and it increased significantly
with atropine. In
awake resting cats, tonic CVNA maintains a low cHR,
but not in the state of anesthesia.
In some of the awake cats, sudden increases in the
CSNA and tachyarrhythmia
associated with excitement
were observed, particularly
in the first occlusion trial.
After the second experimental
trial, such complex responses to occlusion seemed to be inhibited and animals
were in a quiet reclining posture. It is suggested that an
activation of the higher central nervous system modifies
the response patterns of the CSNA to occlusion.
The size and location of the ischemic area are important factors in determining
the responses in preganglionic sympathetic
fibers and hemodynamic variables in
cu-chloralose-anesthetized
cats (8). Both nerve activity
and HR decreased with the global ischemia. In pentobarbital sodium-anesthetized
cats, we occluded the LAD
coronary artery, which induced an ischemic area smaller
than the global but larger than the regional ischemia.
Both the HR and CSNA decreased with LAD coronary
occlusion similar to global ischemia.
Difference of nerve fibers. Although we are interested
in changes in HR and CSNA to occlusion, in this study,
we measured the CSNA in the left cardiac sympathetic
nerve instead of the right cardiac sympathetic
nerve
because the branch of the left inferior cardiac nerve that
distributes
mainly to the left heart contains no efferent
and afferent vagal fibers, whereas the right cardiac sympathetic nerve near the heart does contain these fibers
(1)
I;I the anesthetized state, the nerve activity from the
inferior cardiac nerve near the left stellate ganglion (3),
the preganglionic
nerve activity from the left T3 ramus
(8, lo), the activity from preganglionic fibers to the right
stellate ganglion (7), or the preganglionic
nerve activity
near the left ventral ansa subclavia (6) was recorded.
Different
results among these investigators
may partly
depend on the difference of nerve fibers that distribute
to different regions.
Our previous study demonstrated
that there is a quantitative nonuniformity
in sympathetic
nerve activities to
the heart and kidney in response to coronary occlusion
in anesthetized dogs (21). The sympathetic
nerve activ-
Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on September 18, 2016
duced mainly by the decrease in CSNA.
The differences
of the slopes and intercept
values
before and after atropinization
in the anesthetized state
were evaluated by analysis of covariance (19). There is
no significant
difference
between
the two regression
lines. In the anesthetized
and atropinized
state the
CSNA played a significant
role in the changes in HR
due to occlusion, but the CVNA did not,
10
OCCLUSION
H536
CARDIAC
SYMPATHETIC
ACTIVITY
ities to different functional organs, such as heart, kidney,
spleen, and intestine, in response to baroceptor inputs,
differed quantitatively
(11, 13). In atropinized cats, the
HR changed in parallel with the CSNA (e.g., Figs. 4B, 5,
and 6B). Therefore, our major assumption is that the
CSNA measured in this study is qualitatively
similar to
that in the nerve distributed to the pacemaker cells.
Indirect estimation of efferent cardiac vagul nerve activity. The activity, recorded in the thoracic branch from
Neural mechanism that causes tuchycurdia and bradycardia. During coron .ary occlusion, tachycardia was in-
duced dominantly
in unanesthetized
dogs (15, 16, 18),
but there was no change in HR in anesthetized dogs (6).
In human subjects, tachycardia was induced more by
occlusion of LAD than of the left circumflex coronary
cats, tachycarartery (5, 23). In chloralose-anesthetized
dia was induced during occlusion (8, lo), but bradycardia
was induce ,d with global ischemia (8 ). In the present
study, the transie nt tachycardia (or tachyarrhythmia)
was observed during LAD coronary occlusion in the
awake state when the CSNA increased suddenly and was
significantly associated with excitement (e.g., Fig. 3).
In awake cats, the bradycardia was induced dominantly, even when the CSNA tended to increase. In the
following section, several possible mechanisms
that
might account for the bradycardia during occlusion in
awake cats are discussed.
The first possibility considered is that the bradycardia
was induced by a reciprocal change in CSNA and CVNA,
CORONARY
OCCLUSION
i.e., a decrease in CSNA and an increase in CVNA. For
example, in the conscious state, at 90 s of coronary
occlusion CSNA and HR decreased by 7 and l7%, respectively (Fig. 5). On the other hand, in the atropinized
state at 90 s of occlusion CSNA and HR decreased by 32
and 8%, respectively. The 17% decrease in HR in the
conscious state may not have been induced only by the
7% decrease in CSNA. It is suggested that, during the
late stage of coronary occlusion , the decrease in CSNA
and the increase in CVNA occu r sim ultaneously and in
turn cause such a significant bradycardia.
The second mechanism that might account for bradycardia is an increase in CVNA to the pacemaker region.
In the conscious state, as shown in Figs. 3, 4B, 5, and 7,
the bradycardia occurred rapidly immediately
after the
onset of occlusion without a concomitant
reduction in
the CSNA, but it disappeared after atropinization
(Figs.
4B and 5). Therefore, the possibility that the initial rapid
bradycardia was induced by the increase in CVNA, cannot be neglected. Moreove r, such bradycardia with the
increased CSNA, e.g., Fig. 5, suggests that in the conscious state, at the early stage of coronary occlusion,
there existed a simultaneous
increase in CSNA and
CVNA to the pacemaker cells, but the inhibitory effect
of CVNA, which mediates bradycardia, is larger than the
facilitatory effect of CSNA, which mediates tachycardia.
The third mechanism considered is that CSNA to the
pacemaker cells only decreased during LAD coronary
occlusion. At an early stage of that occlusion in conscious
cats, the CSNA increased (Fig. 5) or was unchanged
(Figs. 3 and 4) at the time of bradycardia and, therefore,
the possibility of a decrease in the sympathetic nerve
activity to the pacemaker cells is less valid. However,
when the CVNA was inhibited in the anesthetized state
or the influence of CVNA was blocked by atropine,
bradycardia was induced mainly by the decrease in sympathetic nerve activity to the pacemaker cells.
In summary, our results suggest that three possible
mechanisms
operate in bradycardia.
The dominant
mechanism depends on the experimental
conditions. In
the conscious state, at the early stage of occlusion, the
increase in CVNA (second mechanism) contributes more
to cause the bradyca rdia, and at the late stage of occlusion a comb ination of th .e de crease in CSNA and the
enhanced CVNA (first mechanism) contributes to cause
a significant bradycardia. On the other hand, the decrease in CSNA (third mechanism) contributes more to
produce the decrease in HR to LAD coronary occlusion
in both the anesthetized and atropinized
cats. In the
awake cats, the t ransient tachycardia w ‘as produced bY a
large increase in CSNA a ssociated with excitement and/
or body movements.
This investigation was partially
supported
by grants-in-aid
for sciScience, and Culture
from the Ministry
of Education,
(no. 60570049) and by research grants for cardiovascular
diseases from
the Ministry of Health and Welfare of Japan.
entific
research
Received
5 March
1985; accepted
in final form
25 March
1986.
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