Circulation Research
MAY
1963
VOL XII
NO. 5
PART ONE
An Official Journal of the Atneriean Heart Association
On Circulatory Control Mechanisms in
the Pacific Hagfish
By Carleton B. Chapman, M.D., David Jensen, Ph.D., and
Kern Wildenthal, B.A.
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• The comparative physiology and anatomy
of the hagfish, a primitive, vertebrate, have
been intermittently under study for about
two centuries. In our own century, it was
Greene's discovery that the branchial heart
of the Pacific (California) hagfish (Eptatretus stoutii) is aneural that set the stage for
renewal of interest in the animal. Greene's
work, published in 1902,1 was confirmed by
A. J. Carlson2 and, in recent years (in Myxine), by Augustinsson and co-workers.3
Greene reasoned that regulation of ventricular activity in the hagfish Ci. . . must depend
upon the conditions which affect the muscle
directly . . . The volume and pressure of the
blood coming to the heart [and other factors]
. . . must have a decided influence on the hagfish heart/' These neglected observations lie
chronologically between Frank's work on the
response of the frog heart to increased filling4
(1895), and Starling's investigations in dogs
which were the basis for what we now call
Starling's Law of the Heart 5 (1915). In the
years of controversy that followed Starling's
sweeping generalizations, the relative roles of
neural control factors, on the one hand, and
of intrinsic myocardial response, on the other.
From the Cardiopulmonary Division of Internal
Medicine, University of Texas Southwestern Medical
School (Dallas) ; and the Division of Marine Biology,
The Scripps Institution of Oceanography, University
of California (La Jolla), New Series.
Supported by an emergency grant from the American Heart Association (Dr. Chapman), and in part
by grants-in-aid from the American Heart Association
and the Alaska Heart Association (Dr. Jensen).
Received for publication November 30, 1962.
Circulation Research, Volume XII, May 1965
have come under sharp scrutiny. Some workers hold that, in the intact mammal, neural
control is dominant and that the role of intrinsic myocardial response is minimal. Others
shift the emphasis to various degrees.
The hagfish circulatory S3rstem, uniquely
incorporating1 a totally aneural ventricle, can
hardly fail to be of interest to the circulatory
physiologist and it seems curious that Greene's
incisive comment was ignored so long. Renewed interest in the animal was stimulated
in 1958 by Jensen 6 who was led to the Pacific
hagfish in part by Greene's observations. In
1961, Jensen concluded that li. . . cardioregulation in the aneural branchial heart of the
hagfish is accomplished by two major factors:
tension as governed by venous return, and a
biochemical factor produced in the heart."
He also found that the usual response of the
branchial heart (or ventricle alone) to slight
distention is to accelerate its rate but that
" . . . this heart has given no indication of
contracting with greater force when the diastolic filling is increased . . . JJ7 The ventricle
might, Jensen thought, even lessen its force
of contraction under conditions of stress.
These results not only suggested the existence of a most unusual circulatory control
system in which Starling's law had no part,
but also raised the possibility that there may
be a type of contractile tissue that does not
exhibit the usual tension-length properties.
The following study was undertaken in the
hope of throwing light on some of these important questions.
427
428
CHAPMAN, JENSEN, WILDENTHAL
FIGURE 1
The Pacific hagfish (Eptatretus stoutii). The head is to the left. The twelve external
gill openings extend from the second to the ninth centimeter marks on the rule.
THE HAGFISH: GENERAL COMMENT
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Myxine glutinosa, the Atlantic hagfish, was
recognized by Linnaeus in 1758 but was
grouped by him with the worms.8 A few years
later (1765) Gunner described the animal as
" a worm that resembles an eel" and commented on its extraordinary ability to produce
slime.0 Home, in 1815, thought the hagfish
to " . . . hold an intermediate place between
. . . the class pisces and the class vermes . . . 7?
(fig. 1). He studied a single specimen brought
from the South Seas and correctly distinguished between what we now call Myxine, on
the one hand, and Bdellostoma, Polistotrema,
or Eptatretus* on the other. Home's careful
description of the structure of the gills and
gill openings was especially valuable^ 16 (fig.
2). The circulatory anatomy of Myxine received the meticulous attention of Anders
Adolf Retains, Professor of Anatomy at the
•The three generic terms are now regarded as
synonymous. Eptatretus10 dating from 1819, has
chronologic priority. Bdellostoma11 was introduced in
1834 and Polistotrema12 in 1881. The most recent
synonym is Dodecatrema.13 The Pacific species (Eptatretus stoutii)14 was named for Dr. Arthur B. Stout,
a practicing physician in San Francisco who served
as corresponding secretary for the California Academy of Science from 1875 to 1878.
t Sir Everard Home, -John Hunter's brother-inlaw, may in fact have utilized some of Hunter's
drawings and writings in preparing the description.
After Hunter's death, Home destroyed a large number of Hunterian manuscripts, of which he was
curator. Among those destroyed was a volume on
the anatomy of fish and works on eels and earthworms. Clift, Hunter's amanuensis, later accused
Home of destroying the manuscripts in order that
his plagarism could never be established.15 The specimen described by Home was brought from the South
Seas by Sir Joseph Banks, Hunter's pupil and
friend, who accompanied Captain James Cook on
his first voyage (1768-1771).
Karolinska Institute in Stockholm in 182217
and 1824.18 In 1841, Berlin's famous physiologist, Johann Miiller, published an extensive
account of the hagfish circulatory system
based on his dissections of dead specimens. He
described the branchial heart and its valves
and confirmed Home's earlier description of
the animal's gill system. He also observed a
"heart-like" expansion of the portal vein (as
had Retzius) 30 but denied that it was independently contractile or that it functioned as
anything1 more than a simple conduit.20 Several years later Miiller observed that the expansion beats rhythmically in the living fish21
and subsequent workers showed that the portal expansion not only has muscle fibers in its
walls but also possesses valves at inlet and
outlet apertures. It is now recognized as a
separate ampullary heart, possibly aneural,
and is called the portal heart. A third heart
of very unusual structure was described by
Gustav Retzius, son of Anders Adolf, in
1890.22 This, the caudal heart, is actually a
pair of flattened sacs between -which is a cartilaginous plate (figs. 3 and 4). 23 The sacs
receive blood from subcutaneous sinuses and
pass it on to veins which unite to form the
caudal vein. The sacs have no muscle in their
walls and are not in themselves contractile.
Their pumping action is attributable, as
shown by Greene,24 to rhythmic contraction
of overlying muscle strips which bend the
anterior end of the cartilaginous plate from
side to side causing alternate filling and emptying of each sac. Valves at inlets arid outlets
of the chambers ensure forward passage of
blood.25 The contractile elements are under
reflex control and cease all movement if the
adjacent spinal cord is destroyed.24
Circulation Research, Volume XII. May 1963
429
CIRCULATION IN THE HAGFISH
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FHJUKE
2
Home's drawing*G of the gill structure of Eptatretus (left), and Myxine (right).
Note the sepcvrate external gill openings of Eptatretus and the paired, combined ones
in Myxine.
Circulation Research, Volume XII, May 1963
430
CHAPMAN, JENSEN, WILDENTHAL
Or
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FIGURE 3
Coronal section of tail of Myxine glutinosa from
Favaro.zs Cr—dorsal expansion of caudal cartilage. Ch—caudal cartilaginous plate. Cu—caudal
heart chamber. Sc—subcutaneous sinus.- M—caudal
heart muscle. Sin—slime organ.
The arrangement of the various hearts in
the hagrfish appears, therefore, to be one in
which the main, or branchial, heart (atrium
and ventricle) is served by two lesser pumping mechanisms, both concerned with venous
return.* Only the caudal pump is known to
be under neural coutrol.
The environment in which the hagfish appears to develop optimally is difficult or impossible to simulate in the laboratory. Said
by Stensio27 to be a degenerate lineal descendant of the earliest vertebrate, it has no jaws
and probably cannot seize living prey for
food. Although it has on occasion been found
in very shallow water, it usually lies virtually
immobile in lightless, frigid marine canyons
for very long periods of time (weeks or
months).28 "When, however, dead or dying
marine animals are brought within range of
its keen olfactory perception, it is capable of
vigorous and effective action. Once it has fed
—and in captivity it lives for up to eight
months without food intake—it again appears
to settle into a state of marine hibernation.
The extent to which metabolic and circulatory
activities are slowed at such times is not
known, but unless disturbed by light21* or mechanical stimuli, the slowing must be profound. Maxwell has shown that the animal
possesses a hyperbolic hemoglobin dissociation
curve and that 95% saturation occurs at oxygen tensions of less than 40 mm Hg.30 Under
''normal" conditions, however, its arterial
blood (dorsal aorta) is about 50% saturated
and venous blood almost totally deoxygenated.
The implications are that it can live actively
at ambient oxygen tension levels of 10 to 20
mm Hg and that its tissues are acclimated to
tensions of no more than 2 to 3 mra.
According to McParland and Munz31 the
Pacific hasrfish is
unique among vertebrates in being isotonic to sea water and having the osmotic concentration of the blood
composed almost entirely of ionic constituents.JJ Serum sodium and chloride account
for 88% of its total osmotic pressure. The
animal has few, if any, natural enemies and
does not appear to be equipped to combat mi*ColeM describes paired contractile venous expansions far forward in the head region and calls them
the fourth heart.
Circulation Research, Volume XII, May 1968
431
CIRCULATION IN THE HAOFI8H
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crobial attacks or to heal wounds. As Papermaster and co-workers have recently shown,3it forms no antibodies when injected with
substances that are antigenic in higher species. Its chief defense mechanisms appear to
be its ability to move about with great vigor
and its remarkable capacity to secrete enormous quantities of protective slime.
The rather complex anatomical relations
between the branchial and the portal hearts
are shown in figure 5. The branchial heart
and its connections are depicted in figure 6.83
The ventral aorta (e), separated from the
branchial ventricle (d) by a bicuspid valve,
leads venous blood to the 12 pairs of gills.
Thence the oxygenated blood is collected in
the dorsal aorta which distributes it to the
tissues and to the subcutaneous sinuses. Return is via the venous system to the sinus
venosus ( a ) . The caudal hearts, whose function is to move blood from posterior subcutaneous sinuses to the caudal vein, have
already been described. The portal heart, receiving most of its blood from mesenteric
veins, also has a connection with the systemic
venous system via the right anterior jugular
vein. Figure 7 shows the general pattern of
the circulatory system.
Microscopically, it is of significance that
the thick branchial ventricular wall is loosely
arranged and possesses no coronary system.
It is also of interest that the tissue contains
large amounts of epinephrine and norepinephrine which are distributed in specific granular
cells similar to those of the mammalian adrenal medulla. 84 ' S5
Methods
Specimens of Eptatretus stoutii were collected
in a tributary of the San Diego trough36 and
were kept in a refrigerator at about 10°C in
buckets of fresh sea water. The animals used were
from 35 to 45 cm long and weighed 60 to 100
g. The wet weight of the branchial ventricle
varied between 75 and 120 mg.
For most experiments, the animals were lightly
anesthetized by putting them into a sea water
environment containing small amounts of tricaine
methane sulfonate. Catheters were then tied firmly
into the nostril so that the gills could be perfused
at regular intervals but continuous perfusion could
not be carried out under the circumstances. The
Circulation Research, Volume XII. May 199$
D
Sc
MUM
4
Cross-section of tail of Myxine glutinosa from
Favaro.iS Dv—superficial dorsal vein. Sc—lateral
subcutaneous sinus. Ct—caudal heart chamber.
M—caudal heart muscle. Ch—raudal cartilaginous
plate.
possibility that the tissues of the hearts were
sometimes hypoxic cannot be ruled out but was
432
CHAPMAN, JENSEN, WILDENTHAI*
TABLE 1
Rates Per Minute of Various Hearts in Four
Specimens of Eptatretus stoutii with "Intact*'
Circulatory Systems Under Laboratory Conditions.
No AV Block Was Present.
Experimental Temp
fl
time
C
0 inin
10 mill
0 mill
FIGURf 5
Diagram of portal and branchial hearts drawn
from specimen of Eptatretus stoutii injected with
gelatin. The small expansion of the tnesenteric
vein at A pulsates independently and serves as
an atrium for the portal heart.
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minimized by the frequency of perfusion and
by the constant application of aerated sea water
directly to the exposed organs. The branchial
and portal hearts were approached from the
ventral aspect through a midline incision, care
being taken not to injure the branchial vessels.
Catheters were carefully lined up with the axes
of the vessels to be entered (ventral and dorsal
aortas and posterior cardinal vein) and their
distal ends fixed with pins to the dissecting board.
The tips were then introduced into the desired
vessel and were tied in place. For taking pressures
directly from the branchial ventricle, atrium, or
portal heart, short lengths of catheters tipped
with N"o. 24 hypodermic needle points were used.
The needles were inserted directly through the
walls of the chambers to be studied.
It is hardly possible to place a catheter or
needle directly into the lumens of the caudal heart
sacs. Instead, needles were inserted so that their
open ends lay just over the sac itself. While no
direct pressures could be obtained in this way,
very satisfactory records of caudal pump activity
were nevertheless recorded.
When catheters were in place, the animal and
the board on which it rested were transferred
to a table where strain gauges were already
mounted. The heights of the gauges were then
adjusted and connection with the catheters was
established; great care had to be taken to avoid
pulling catheter tips out of the vessels in which
they rested. Temperatures were controlled approximately by frequent applications of sea water held
at 8° to 10°C.
Isolated branchial heart preparations were prepared by passing catheters into the ventricular
lumen through the ventral aorta for pressure measurements. A second catheter was passed into the
ventricle via the atrium and was tied in place with
a ligature in the A-V groove. The cannulnted heart
5 min
10 min
11
16
16
16
16
18
18
Branchial
ventricle
Portal
13
24
30
30
25
26
20
30
24
23
25
24
22
26
heart
Caudal
heart
0
0
88 (or 44)
88 (or 44)
88 (or 44)
0
0
was then removed and suspended in cold sea water.
The pressure cannula was connected to a strain
gauge and the ventricular catheter to an injection
device for delivering precisely measured quantities
of cold sea water.
Results
The rates of branchial and portal hearts
appear to be dependent on temperature, as
shown earlier by Jensen.7 In the present work
four isolated hearts held at 8° to 15°C showed
rates of 5 to 12 per minute. Raising the temperature to 20 °C or higher brought rates up
to 24 per minute.
Under laboratory ( ' resting'' conditions,
rates for the three hearts in four different
' * intact J ' specimens of Eptatretus stoutii
were as shown in table 1.
It was repeatedly noted that in isolated
heart preparations and in the "intact" animal , rate always slowed and sometimes
stopped if return flow was at a very low level.
The easiest way to restart a quiescent heart
was to perfuse it. And reperfusion of a heart
beating at a very slow rate usually, but not
always, caused the rate to increase.
Of great interest was the fact that branchial ventricular rate seemed to depend to an
important extent on the degree of A-V block
at any particular time. Degrees of block up
to 6 :1 were observed and, in general, the degree of block tended to increase when the
ventricle was overdistended (fig. 8). Very
high degrees of block often indicated deterioration of the preparation. In other instances,
where the ventricle was not being perfused
Circulation Research, Volume XII, May 196S
434
DORSAL
CHAPMAN, JENSEN, WILDENTfJAL
AORTA
(OXYGENATED)
Branchial Ventricle v
FIGURE 7
Portal Heart*
Schematic drawing of circulatory apparatus of
42/min
60/min
Eptatretus stoutii.
Caudal Heart«
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!„-
72 /mln
-1.
5 sec
0.6
0.9
1.3
Amount injected,ml
l.S
FIGURE 10
FIGURE 8
Effect of overdistention of the branchial heart
by continuous injection of sea mater into the posterior cardinal vein, beginning at zero time. Note
the initial slowing (owing to increase in AY block)
and the appearance of bigeininy. (Retouched.)
Nonalternating caudal heart beat (negative deflections) (below). Branchial and portal heart rates
are unusually rapid.
/mln
Branchial Ventricle
23/min
Heart
Portal H
earty
43/min
43/min
I t
Caudal
Heart.
60 or 3 0 / m i n
Caudal Heart 78 or 3 9 / m i n %
30 tec
FIGURE 11
FIGURE 9
Alternating caudal heart beat (beloio). The small
upstroke just before the main upstroke of brachial
ventricular pressure is due to otrial contraction.
larity (fig. S) or it may produce the result
shown in figure 14 in which ventral aortic
systolic pressure rises from 6 mm to a maximum of 21 mm Hg. Change in diastolic pressure, however, is much less marked. In yet
another approach (fig. 15), successive injec-
Spontaneous cessation of caudal heart beat
(below). The isolated beat was followed by six
minutes of inactivity.
tioiis of increasing amounts of sea water into
the posterior cardinal vein of the "intact"
preparation at 30-second intervals yield response curves the steepness of which depends
on the amount by which each increment is
increased. Diastolic pressure rises with each
increment but not as much as sj'stolic. Use
of still larger increments, as in table 2, occaCirculation Research, Volume XII, May 1968
433
CIRCULATION IN THE HAGFISH
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(and may, therefore, have been hypoxic) the
degree of block was reduced when even small
amounts of fluid were presented to the ventricle. The result was usually an increase in
rate.
Portal heart rate ranged between 15 and 60
per minute but usually fell below 30. There
was some evidence that overdistention of the
chamber produced marked irregularity in its
rhythm.
The caudal heart, in the undisturbed "intact" preparation, is often completely inactive. When in action, its rate is usually faster
than that of the branchial or portal hearts.
Frequently, alternans patterns (fig. 9) were
obtained owing to the reciprocal action of the
two pumps. In other tracings, a clear single
impulse is seen (fig. 10). Irregularities of
the caudal rhythm and rate are common.
Slowing for a few seconds often precedes total
cessation of activity (fig. 11). "When conditions are ripe for resumption of activity, the
hearts usually start abruptly at or near the
rate that prevailed in the last period of activity. Restarting of the caudal heart beat
often followed perfusion of the gills, washing
of the tail region with cold water, and pricking the intact skin with a pin. Periods of
quiescence, in the absence of external stimulation, lasted from two to thirteen minutes.
Besting systolic pressures in the branchial
ventricle and portal heart usually were less
than 1 mm Hg. In the branchial ventricle, a
resting range of 0.7 to 5.9 mm Hg was noted.
Under conditions of maximal or near-maximal load, the branchial ventricle, whether
isolated or in situ, frequently drove pressures
up to 20 mm Hg and on one occasion an isolated heart reached 30.8 mm Hg. Similarly,
the branchial atrium and the portal heart,
when moderately or maximally distended,
were consistently capable of developing pressures up to about 2.0 mm Hg.
The response of the isolated branchial ventricle to filling is shown clearly in figure 12,
which represents a repetition of Frank's classical experiments with the frog heart. It will
be seen that the isolated ventricle, contracting
Circulation Research, Volume XII, May 1963
/t
FIGURE 6
Branchial heart and connections of Myxine glutinosa from Erik Miiller.33 a—sinus venosus. b—
atrium, c—AV canal, d—ventricle, e—ventral aorta,
f—main jugular vein, g—left anterior cardinal
vein, h 1-hi—hepatic veins, i—inferior intestinal
vein, j—ovarian vein, k—posterior cardinal vein.
virtually isovolumically, develops higher pressure with each increase in amount of sea water
injected (0.015 ml increments). There was,
however, no descending limb. In figure 13,
one sees the effect of injecting 0.03 ml of sea
water into the posterior cardinal vein of an
"intact" preparation. The ventricular systolic pressure more than doubles between
beats. Continuous injection of sea water into
the posterior cardinal vein (2.0 ml over a 30second period) may cause ventricular irregu-
435
CIRCULATION IN THE HAGPISH
-I 25
15
10
"sec
1
FIGURE 12
FIGURE 13
2
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Family of pressure curves produced by isolated
branchial ventricle, contracting isovolumically.
Curve 1 was a> control beat; Curve 2 followed
the injection of 0.015 ml of sea water. The preparation was then allowed to return to zero diastolic
pressure and 0.030 nil was injected (Curve 3).
Curve 4 resulted from an injection of 0.045 ml,
Curve 5 from 0.060 nil} and so on. Curve 9 resulted
from an injection of 0.120 ml. Temperature 11°
C throughout, (Redrawn^ from original recordings).
Response, in terms of ventral aortic pressure, to
injection of 0.030 ml sea' water into posterior
cardinal vein at A.
20-
15-
sionally is associated with a descending limb
but it is doubtful that such an effect is seen
unless there is a concomitant increase in pulse
rate. The effect of temperature on the isovolumic response of the isolated ventricle to
filling does not seem to be marked (table 3)
in the range of 11° to 21°C.
Epinephrine in various concentrations, injected into the posterior cardinal vein or into
the isolated ventricle produced no effect beTABLE 2
Response of Branchial Ventricle (in Terms of
Maximal Aortic Pressure) to Injection of 0.075
ml of Sea Water Every 30 Seconds.
Total injected
ml
Control
.075
.150
.225
.300
.375
.450
.525
.600
Maximal pressure
mm Hg
7.0
Rate
beats/min
20.4
21.2
20.4
19.4
18.6
1S.1
17.8
17.1
Circulation Research, Volume XII, May 196S
21
24
2-4
24
27
30
30
30
30
10-
5-
20
40
Time , sec
FIGURE 14
60
80
Behavior of ventral aortic pressure when a total
of 2.0 nil sea water was injected conthnioushj
into the posterior carddn-al vein. Very little effect
on cardiac rate was seen and diatstoMc pressure
response was much smaller than systolic.
yond that attributable to volume alone (fig.
16). Reserpinization produced very little
change in the isovolumic response of the
branchial ventricle to volume stress (table 4).
There was some evidence, however, that the
ventricular response declined in some animals
after reserpinization and that it was partly
restored toward control values by the use of
epinephrine (fig. 17).
436
CHAPMAN, JENSEN, WILDEWTHAL
sea water, nonreaerpinized heart
- - • lO~ 5 g/ml epinephrine
reserpinixed heart
__» sea water ,
reserpinixed heart
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1
1
1
1
2
Minutes
FIGURE 15
—1
I
3
Mammal pressure response to serial injections
of increasing volumes of sea water into posterior
cardinal vein of "intact" preparation. Isotonic
contraction. Lower curve represents response when
increments of 0.030 ml were used. Upper curve
shoios response to 0.060 ml increments from the
third to the eighth injections.
30-
2520-
15-
0044
O088
Injection
0tl32
increments,
ml
FIGURE 16
Effect of epinephrine on maximal pressure response to serial injections of increasing volumes
of sea water. No significant difference between the
response under the various conditions is seen.
I
I
I
O.O11
0.044
O.O66
Volume
I
I
O-O8S O.11O
injected , ml
FIGURE 17
Effect of reserpine and epinephrine on isolated
heart. The top curve is the control (untreated)
response to serial injections of increasing volumes
of sea water. The bottom curve shoios the response
after reserpinization (2.5 mg/ml sea water of
Serpasil in the bath in which the heart was suspended and injected into the ventricle; treatment
continued for an hourj the heart was then
thoroughly washed out and put into a bath of
fresit sea water). The middle curie shows the
response of the reserpinized heart to serial injection of sea water containing epinephrine (10~5
9/ml).
Resistance to flow across the aortic valve
seemed to be negligible as judged by the pressure drop from ventricle to aorta. Under
"resting" conditions it was not measurable
with accuracy and when perfusion (via the
posterior cardinal vein) was maximal, it was
no more than 1 or 2 mm Hg (fig. 18). Resistance to flow in the gill vascular system was
greater but highly variable. Under "resting"
conditions, pressure drop from ventral to dorsal aorta was regularly 2 to 3 mm Hg and
was greatly increased when the branchial
heart ("intact' 3 preparation) was perfused
(fig. 19). When perfusion was masimal; the
drop from ventral to dorsal aorta rose as high
as 12 mm Hg but tended to fall as perfusion
was continued.
Circulation Research, Volume XII, May 1963
437
CIRCULATION IN THE HAGFISH
FIGURE 18
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Pressure drop from branchial ventricle to ventral
aorta. Ventricular calibration is at left} aortic
at right. At A, 0.30 ml of sea water was injected
into posterior cardinal %ein. Note the effect on
atrial pressure (small rise at the beginning of the
ventricular upstroke) as well cos on ventricular
response.
FIGURE 19
Pressure drop from ventral aorta (calibration at
right) across the gills to dorsal aorta (calibration
at left). At mark (top), 0.15 ml sea water was
injected into the posterior cardinal vein.
bond* 1 rvt*a »6 mini
of* • 9 1 mtn |
The electrocardiogram -varies according to
placement of the electrodes. Using needle
electrodes placed on each side of the hranchial
ventricle (RA on the right, LA on the left),
dipolar tracings were obtained as shown in
figure 20. The main deflections (QRS) and
the preceding P waves are easily seen. Another deflection, diphasic in form, stems from
the portal heart. PR intervals Avere highly
variable but were usually about one second.
In some instances they were much longer. It
proved to be impossible to obtain caudal electrocardiograms.
Discussion
The key finding in the present study is that
the aneural branchial ventricle, which is the
TABLE 3
Response of Isolated Branchial Ventricle (Maximal
Pressure in mm "Eg) to Increasing Increments of
Filling at Various Temperatures. The Experiments
at 13° and cut 21° Were Done on the Same Heart.
Those at 11° and 14° Were Done on Different
Hearts.
Increment of
filling (ml)
11°
13°
14°
21°
Control
.015
2,0
10.3
1.8
2.4
1.2
5.2
.030
15.2
.045
.060
16.5
18.7
20.2
11.0
12,4
16.1
18.8
21.7
10.2
17.3
21.0
23.6
11.6
17.5
19.2
19.8
.075
Research, Volume Xltt Maty 1963
1
Q IS
f 1 or
tor
QHS
tar
p
tor
—"W
FIGURE 20
Electrocardiogram taken with needle electrodes on
each side of the branchial ventricle. Por indicates
complexes attributable to activation of the portal
hewrt. PQ interval measures about 0.75 sec.
primary driving force of the hagfish circulatory system, responds to increased filling by
increasing its force of contraction precisely
as does the isolated frog or mammalian ventricle. The unperfused hagfish ventricle,
whether isolated or in situ, tends to beat very
slowly or to stop altogether for relatively
long periods. When reperfused, it readily begins beating again but may require several
seconds to return to its previous level of activity. This phenomenon was also observed
b}r Jensen7 and may account in part for the
discrepancy between his earlier work and the
present study.
The nearest approach to "resting" physiological conditions under laboratory conditions
was achieved by Johansen who worked with
unanesthetized Myxine glutinosa at temperatures of 4° to 7°C.37 The rates of branchial
438
CHAPMAN, JENSEN, WILDENTHAL
TABLE 4
Branchial Ventricular Eesponse (Maximal Pressures in Ventral Aorta) to Continuous
Injection of Sea Water, Before and After Reserpinization (2 X 10~5 g/wil Injected
into Posterior Cardinal Vein and Left in the System for Two Hours). Temperature
12°C Throughout. "Intact" Preparation.
Time
(sec)
0
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15
30
45
60
75
90
105
120
135
150
165
injected
(ml)
'•
0
0.22
0.44
0.66
0.88
1.10
1.32
1.54.
1.76
1.9S
2.20
2.42
Before reserpine
Pressure
Rate/m in
Diast.
Syst.
7.0
5.2
15.0
15.0
15.5
15.6
15.4
16.0
16.3
16.4
16.5
13.8
14.6
5.5
4.4
12
9
8
4.2
8
4.4
4.7
4.9
O.I
6.3
5.1
8.2
8.7
6
5
11
11
15
20
33
33
and portal hearts he observed were quite similar to those found in the present study. The
participation of periodic contraction of gill
musculature in the propulsion of blood from
gill capillaries through the systemic arterial
tree, as reported by Johansen, was not substantiated. It is possible that the anesthetic
abolished the effect but it is also possible that
the unanesthetized animal produced so much
slime that external gill apertures became occluded; periodic contraction of gill musculature may, therefore ; have been directed at
clearing the external openings rather than at
the propulsion of blood.
In any event, the branchial ventricle proved
to be able to deal quite effectively "with relatively enormous volume loads and, when contracting isovolumically, to develop extremely
high pressures. There is little evidence, therefore, that it requires a booster effect in the
outflow (arterial) circuit.
It proved to be difficult to produce the descending limb described by Frank and Starling j the hagfish branchial ventricle usually
responded to stepwise increase in filling by
increasing its force of isovorumic contraction
until it suddenly stopped altogether. On being allowed to empty, it usually began beating
again without difficulty. In the " i n t a c t "
preparation, ventricular arrhythmia frequently occurred as the ventricle became overloaded
After reserpine
Pressure
Rate/min
Syst.
Diast.
3.0
2.8
13.4
15.8
15.8
15.5
15.7
16.2
16.4
15.2
14.7
14.5
14.7
6.8
4.3
4.5
4.7
4.7
4.8
4.8
6.1
5.9
6.2
6.1
9
1
1
10
10
11
12
12
18
18
18
18
but failure in the usual sense was not observed.
In agreement with Bloom et al.,34 the branchial heart proved to be quite insensitive to
epinephrine, even in high concentrations. Pretreatment with reserpine seemed to have very
little effect on ventricular sensitivity to epinephrine. It is possible that reserpine caused
a diminution in the vigor with which the ventricle responded to increased filling and that
subsequently, epinephrine merely restored it
to its normal functional status. In any case,
the response to epinephrine in no way resembled that found in the frog heart by Segall
and Anrep. 38
The response of the portal heart resembles
that of the branchial in that it increases its
force of contraction as filling is increased. It
must, therefore, respond, under normal conditions, in the same way to increased filling from
mesenteric veins after the animal has fed. Its
rate is more constant than is that of the other
hearts and not infrequently it continued to
beat when the other hearts were temporarily
quiescent. When overloaded it, like the branchial ventricle, sometimes beats irregularly.
The caudal hearts, as intimated earlier, are
quite unpredictable under laboratory conditions. Greene's demonstration that destruction
of the cord causes permanent cessation of
caudal heart activity, plus the observation
Circulation Research, Volume XII, May 196S
439
CIRCULATION" IN THE HAGFISH
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that various external stimuli seem to be able
to bring about resumption of activity, support
the concept that the caudal hearts are reflexly
controlled. It seems likely that distention of
the lateral sinuses, among other stimuli, can
activate the paired pumps although this is not
certain.
The circulatory control system of the hagfish appears, therefore, to embody both neural
and myocardial features. The animal is unique
primarily in that the two control principles
are anatomically separate. Neural mechanisms
in this very primitive, elongate creature operate primarily on the venous side of the circulation presumably making caudal and possibly portal hearts responsive to venous
over- or. underfilling. They, in turn, control
the branchial heart by altering the amount of
return flow. The branchial ventricle thus
seems to be controlled solely by volume signals
and the hagfish circulatory apparatus seems
to utilize the Frank-Starling principle as its
primary means of response to stress. Neural,
and possibly hormonal, factors come to bear
on the property of intrinsic myocardial response less directly than in the mammal. Tn
higher members of the animal kingdom, both
neural and myocardial mechanisms come to
be intricately intertwined in the myocardium
itself; in the hagfish they are neatly separate
and distinct.
Finally, the astonishing facility with which
th e h agfi sh ci rcul atory system can cb an ge
from almost total quiescence to vigorously effective activity richly deserves serious study.
The loose anatomical arrangement of myocardial fibers, permitting easy perf vision from
either side of chamber walls, is probably part
of the explanation and, in a sense, renders
the ventricle more adaptable and less vulnerable than those that require coronary circulations. But.there is also the possibility that
the nature of the contractile tissue is different
and that, as Jensen intimates, special hormonal factors play an important role. In any
event, studies on the species suggest that a
great deal is to be gained from revival of the
comparative physiological approach to circulatory function and control.
Research, Volume XII, May 196S
Conclusions
1. The branchial atrium and ventricle, and
the portal heart of Eptatretus stoutii (the Pacific hagfish) respond to increased filling by
increased force of contraction as judged by
maximal pressures developed.
2. The branchial ventricle is capable of increasing maximal pressure from less than 1
mm Hg to well over 20 mm Hg within several
beats.
3. Greene's suggestion that the caudal
hearts are under reflex control is borne out,
if not actually proved, by the action of certain external somatic stimuli. The quiescent
caudal heart is often restored to vigorous activity by such stimulation.
4. Factors controlling the portal heart are
not understood but it seems to be the most
constant, with regard to rate, of any of the
hearts.
5. The probability that neural factors act
on ampullary (venous return) hearts and that
the branchial ventricle responds solely to volume stimuli is supported by present findings.
Acknowledgment
The able technical assistance of Mr. James Maggert is gratefully acknowledged. We are also much
indebted to Dr. Sven Eliasson for generous assistance with Scandinavian literature and to Mrs. Jack
Collins for Latin translations.
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Circulation Research, Volume XH, May X96$
On Circulatory Control Mechanisms in the Pacific Hagfish
CARLETON B. CHAPMAN, DAVID JENSEN and KERN WILDENTHAL
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Circ Res. 1963;12:427-440
doi: 10.1161/01.RES.12.5.427
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