Download Print - Circulation Research

81
Effect of Vagal Stimulation on the Overflow of
Norepinephrine into the Coronary Sinus during
Cardiac Sympathetic Nerve Stimulation in the Dog
MATTHEW N. LEVY, M.D.,
AND BENJAMIN BLATTBERG,
M.S.
Downloaded from http://circres.ahajournals.org/ by guest on May 8, 2017
SUMMARY In anesthetized dogs with the chest open, supramaximal stimulation of the left cardiac sympathetic nerves at 2 and 4 Hz
produced an increase of 40-50% in ventricular contractile force (CF)
and of 40-65% in coronary sinus blood flow. At these frequencies of
stimulation, norepinephrine (NE) overflow into the coronary sinus
was 29.8 ± 5.1 (SE) and 54.9 ± 13.2 ng/min, respectively. Concurrent, supramaximal vagal stimulation, at a frequency of 15 Hz, had
no significant effect on coronary sinus blood flow, but caused a 25%
reduction in CF and a 30% decrease in NE overflow. The changes in
CF and NE overflow evoked by vagal stimulation were prevented by
atropine. These results are consistent with the hypothesis that there
are muscarinic receptors on the postganglionic sympathetic terminals
in the walls of the ventricles. Acetylcholine released during vagal
stimulation combines with these receptors, causes a reduction in the
liberation of NE, and thereby attenuates the positive inotropic
response.
COMPLEX interactions between the sympathetic and parasympathetic innervations of the heart are known to occur.
One type of cardiac autonomic interaction has been termed
"accentuated antagonism": it is characterized by a progressive attenuation of the cardiac effects of activity in one
division of the autonomic nervous system as the level of
antagonistic activity in the other division is increased.1 Two
types of mechanisms have been proposed to account for
accentuated antagonism: (1) a cholinergically mediated
reduction in the quantity of norepinephrine (NE) released in
response to a given level of cardiac sympathetic activity,2"4
and (2) a cholinergically mediated reduction in the cardiac
response to a given quantity of released NE.5"9
Our present series of experiments was designed to test the
first hypothesis. Previous experiments by Loffelholz and
Muscholl2 on isolated, perfused rabbit hearts demonstrated
that an infusion of acetylcholine caused a reduction in the
quantity of NE released in response to a given stimulus to
the cardiac sympathetic nerves. In a subsequent study on
isolated rabbit atria, these investigators3 showed that the
quantities of acetylcholine liberated during vagal stimulation were adequate to curtail the rate of release of N E during
sympathetic activity. In that study, the ventricles were
removed because it was thought that "their vagal innervation is poor." 4 However, numerous studies have shown that
vagal stimulation does have a significant negative inotropic
effect on ventricular contractility.10"16 Furthermore, it has
been demonstrated that this effect is more pronounced the
greater the background level of cardiac sympathetic
activity.1- "• l4- 16 In the present study, we have conducted
tests to determine whether this sympathetic-vagal interaction, as it involves ventricular contractility, is at least
partially dependent on a vagally mediated reduction in NE
release at sympathetic postganglionic terminals.
Methods
From the Department of Investigative Medicine, Mt. Sinai Hospital and
Case Western Reserve University, Cleveland, Ohio.
Supported by Grant HL 15758 from the U.S. Public Health Service.
A preliminary report of this work was presented at the International
Conference on Cardiovascular System Dynamics, Valley Forge, April 1975.
Received June 9, 1975; accepted for publication October 17, 1975.
All experiments were conducted on mongrel dogs anesthetized with sodium pentobarbital, 30 mg/kg, iv. To minimize
the effects of withdrawal of blood for chemical determinations, dextran was infused continuously.
The chest was opened through the 4th intercostal space.
Heparin, 500 units/kg, was injected intravenously to prevent
blood coagulation, and a modified Morawitz cannula was
introduced into the coronary sinus through the azygos vein.
The tip of the cannula was fixed in position by a suture
placed around the coronary sinus, within 1 cm of its ostium.
Consequently, most of the coronary sinus blood was drained
by the cannula. The coronary venous blood was conducted
from this cannula through the extracorporeal probe of an
electromagnetic flowmeter (Biotronix) and was returned via
the right external jugular vein. Right ventricular force was
recorded by a Walton-Brodie strain gauge arch sutured
about halfway between the apex and base of the heart and
about I or 2 cm lateral to the anterior descending coronary
artery. The two feet of the arch were aligned in parallel to
the anterior descending coronary artery. Contractile force,
femoral arterial blood pressure, and coronary sinus flow
were recorded on a Brush Mark 260 oscillograph.
The cervical vagosympathetic trunks were transected and
shielded bipolar palladium electrodes were applied to the
cardiac ends of both nerves. Tight ligatures were applied
about the upper poles of both stellate ganglia: previous
experiments" have shown that, in the dog, this procedure
virtually abolishes the tonic sympathetic discharge to the
heart. A shielded bipolar electrode was placed about the two
limbs of the left ansa subclavia. The left side was selected for
stimulation because it has been demonstrated 17 that the
positive chronotropic effects of stimulating the left cardiac
sympathetic fibers are small compared to those caused by
right-sided stimulation. The ansa subclavia was stimulated
by means of a Grass S4 stimulator with supramaximal
(usually 8 V) rectangular pulses, 1 msec in duration, for each
of two periods of 15 minutes. There was a rest period of 10
minutes between the two periods of sympathetic stimulation.
82
CIRCULATION RESEARCH
Two sets of experiments were conducted. For the first we
used a group of seven dogs which weighed, on the average,
20.3 ± 0.6 (SEM) kg; their hearts weighed 155 ± 9 g.
Frequencies of 2 and 4 Hz were used during the 15-minute
periods of sympathetic stimulation; the order of application
of these two frequencies was selected by chance in each
experiment. For the second group of experiments we used
six dogs which weighed, on the average, 21.8 ± 0.8 kg; their
hearts weighed 153 ± 8 g. During both 15-minute periods of
sympathetic stimulation we used a frequency of 2 Hz.
However, during the 10-minute rest period between the
two stimulation periods, atropine sulfate (1 mg/kg, iv)
was injected. Just before and just after the second period of
stimulation we verified that this dose of atropine was
adequate to abolish completely the bradycardia or asystole
produced by strong vagal stimulation.
Downloaded from http://circres.ahajournals.org/ by guest on May 8, 2017
Throughout each period of sympathetic stimulation (except in the experiments conducted after the injection of
atropine), the atria and ventricles were paced synchronously
at a constant rate that just exceeded the rate produced by
sympathetic stimulation. Each of the 15-minute periods of
sympathetic stimulation was subdivided into five consecutive 3-minute periods. The first, third, and fifth such periods
consisted of the sympathetic stimulation alone, at either 2 or
4 Hz. During the second and fourth periods, the vagi also
were stimulated. The two vagal electrodes were connected in
parallel to the stimulus isolation unit of a Grass S4
stimulator. The stimuli were supramaximal (usually 10 V), 1
msec in duration, and applied at a frequency of 15 Hz.
NE was assayed in arterial and coronary sinus blood by
the fluorometric methods of Anton and Sayre 18 and Laverty
and Taylor. 19 Blood samples were collected at the end of
each 3-minute interval during the two 15-minute periods of
cardiac neural stimulation. The rate of endogenous NE
overflow during neural stimulation was computed as the
product of the coronary sinus blood flow and the NE
concentration in the coronary sinus blood. In computing the
rate of NE overflow, it was assumed that the small quantity
of NE in the coronary arterial blood was completely cleared
during its passage through the coronary vascular bed. We
believe this is a reasonable assumption. However, the results
presented below do not depend appreciably on the validity of
this assumption. In the first group of animals the NE
concentrations in the arterial blood were only 18 ± 3% (SE)
and 15 ± 3% of the levels in the coronary sinus blood during
sympathetic stimulation alone at 2 and 4 Hz, respectively. In
the second group of animals the NE concentrations in the
arterial blood were 13 =t 3% and 17 ± 3% of the
concentrations in the coronary sinus blood during sympathetic stimulation alone before and after atropine, respectively. Under each of these conditions, moreover, superimposition of vagal stimulation had no detectable effect on the
NE concentration in the arterial blood. Hence, computing
NE overflow either on the basis of the coronary sinus NE
concentration or on the basis of the atrioventricular concentration difference would not substantially influence the
overall results.
Results
Figure I is a record of the effects of sympathetic and vagal
stimulation on myocardial contractile force (CF) in a
VOL. 38, No. 2, FEBRUARY
1976
representative experiment. Sympathetic stimulation (beginning at arrow 1), increased CF by 48% above the control
value. With comcomitant vagal stimulation (arrow 2), CF
fell to 30% above control (panel C). On the cessation of
vagal stimulation (arrow 3), CF increased again to 42%
above control (panel D). Thus, the increment in CF above
control during combined sympathetic and vagal stimulation
was only about 65% of the average increment during the
preceding and following periods of sympathetic stimulation
alone. In other words, vagal stimulation appeared to reduce
the positive inotropic effect of a given level of sympathetic
stimulation by about 35%.
The composite data for the seven animals in the first series
of experiments are presented in Figure 2. The heights of the
open bars represent the mean values of the various responses
during the three alternate 3-minute periods of sympathetic
stimulation alone. For each animal the values during these
three periods were averaged. The heights of the diagonally
hatched bars represent the mean values of the responses
during combined vagal and sympathetic stimulation. In each
experiment, the values of the two periods of combined
stimulation were averaged. The paired Mest was used to
determine the significance of the various differences; hence,
the standard errors of the various mean values are not
incorporated in the figure.
During sympathetic stimulation alone at a frequency of 2
Hz, CF increased by 47.3 ± 6.2% (SE). When the vagi were
stimulated also, there was a consistent reduction in CF from
the peak attained with sympathetic stimulation alone (Fig.
2). When the differences in CF during sympathetic stimulation alone and during combined vagal and sympathetic
stimulation were measured for each animal, the mean
difference for the entire group was found to be 10.4 ± 1.2%
(SE) of the mean control CF (P < 0.001).
During sympathetic stimulation alone at 4 Hz, CF
increased by 38.9 ± 9.3% above the control value. This value
was somewhat less than that obtained with stimulation at 2
Hz. This result is unusual, in that during preliminary
observations an immediate increase in stimulation frequency
from 2 to 4 Hz always was followed by an increase in CF,
and a reduction in stimulation frequency from 4 to 2 Hz was
always followed by a decrease in CF. The smaller response
at 4 Hz than at 2 Hz observed in Figure 2 was mainly
attributable to the tendency for the response to become
SVMP.
STIM.
12
VACAL
STIM.
13
STOP
VAG. STIM.
FIGURE I The changes in right ventricular contractile force during
cardiac neural stimulation in a representative experiment. Beginning at arrow I, the left ansa subclavia was stimulated at 8 V, I
msec, 2 Hz, for 15 minutes; 3 minutes later (arrow 2) both
vagosympalhelic trunks were also stimulated at 10 V, I msec, 15 Hz
for a train duration of 3 minutes; arrow 3 marks the end of that
period of vagal stimulation. Atria and ventricles were paced
synchronously at a frequency of 160 beats/min.
CARDIAC NOREPINEPHRINE RELEASE/Levy and Blattberg
vagal stimulation did not significantly alter the coronary
sinus blood flow at either stimulation frequency.
The overflow of NE into the coronary sinus was 29.8 ±
5.1 ng/min during sympathetic stimulation alone at 2 Hz.
The mean difference in NE overflow during sympathetic
stimulation alone and during combined vagal and sympathetic stimulation was 9.9 ± 2.8 ng/min (P = 0.001, by the
paired /-test). Thus the superimposition of vagal stimulation
decreased the NE overflow by about one-third of the rate
found during sympathetic stimulation alone. The rate of NE
overflow was 54.9 ± 13.2 ng/min during sympathetic
stimulation alone at 4 Hz. This rate was about twice that
which was found at a frequency of 2 Hz. The mean
difference in NE overflow during sympathetic stimulation
alone at 4 Hz and during combined sympathetic and vagal
stimulation was 16.1 ± 2.6 ng/min (P < 0.001), a reduction
of about 29% of the value during sympathetic stimulation
alone.
I- O °
z ee- 120
OO °
U "-#100
:
40
i
i
30
, c 20
> c
10
O
-l<J to £
40
111 CC £
OC UJ ^
83
20
Downloaded from http://circres.ahajournals.org/ by guest on May 8, 2017
O > o)
z O c
2 Hz
I CONTROL
4 Hz
I—I SYMP.
I
I ALONE
1 S Y M P. +
I VAGUS
FIGURE 2 The mean right ventricular contractile force, coronary
sinus blood flow, and norepinephrine overflow in seven dogs during
a prestimulation control period, during supramaximal sympathetic
stimulation at 2 and 4 Hz, and during supramaximal vagal
stimulation at 15 Hz combined with sympathetic stimulation. In
each animal sympathetic stimulation at each frequency was continuous for 15 minutes but was subdivided into five consecutive
3-minute observation periods. The responses to sympathetic stimulation (unshaded bars) in each animal are the averages of the
responses during periods I, 3, and 5. The vagi were stimulated
concomitantly with the sympathetic nerves during periods 2 and 4.
The responses to combined neural stimulation (diagonally hatched
bars) in each experiment are the averages of the responses during
periods 2 and 4.
In the second series of experiments there were two
15-minute periods of sympathetic stimulation at 2 Hz,
separated by a 10-minute rest period. Atropine sulfate, 1
mg/kg, was given near the beginning of the rest period, and
cardiac pacing was discontinued. The responses to neural
stimulation are displayed in Figure 3. Before atropine, the
responses resembled Jhose during sympathetic stimulation
at 2 Hz in the first series (Fig. 2). CF increased by 24.1 ±
5.9% (SE) above the control level in this second group of
animals during sympathetic stimulation alone. With the
addition of vagal stimulation, the mean reduction in CF was
10.8 ± 2.3% of the mean control CF (P < 0.001, by the
paired /-test).
Coronary sinus blood flow increased from a mean control
P
2
<
attenuated with the passage of time at the higher of these
two frequency levels. The values in Figure 2 represent the
averages over the three periods of sympathetic stimulation.
Throughout the 15-minute period of continuous sympathetic
stimulation at 2 Hz, the increment in CF was well maintained. At 4 Hz, however, there was usually a progressive
decline in CF. Such progressive reductions in response to
sympathetic stimulation at the middle to upper levels of the
physiological frequency range have been observed
previously.20"22
Of much greater relevance to the present study is the
response to superimposed vagal stimulation. During continuous sympathetic stimulation at 4 Hz, just as at 2 Hz, the
addition of vagal stimulation produced a consistent reduction in CF. For the entire group of animals the mean
difference in CF during sympathetic stimulation alone and
during combined vagal and sympathetic stimulation was
10.2 ± 4.2% of the control CF (P = 0.025). Thus, the mean
difference in CF produced by vagal stimulation during
sympathetic stimulation at 4 Hz was virtually the same as
the difference found for sympathetic stimulation at 2 Hz
(10.4%).
The coronary sinus blood flow increased substantially
during sympathetic stimulation; the increment was greater
at 4 Hz than at 2 Hz (P = 0.05). However, superimposing
160
=140
100
m
50
40
30
20
O
-i-
U m E
5
•o
"J I E
oc iu ^.
O > en
Z Oc
10
0
30
20
10
0
BEFORE
AFTER
ATROPINE
ATROPINE
r-|SYMP.
CONTROL |_I ALONE
S3 VAGUS
FIGURE 3 The mean right ventricular contractile force, coronary
sinus blood flow, and norepinephrine overflow in six dogs before
and after the intravenous administration of atropine sulfate, 1
mg/kg. The left cardiac sympathetic nerves were stimulated
supramaximally at 2 Hz for 15 minutes both before and after
atropine. Each stimulation period was subdivided into five intervals,
as described in the legend for Figure 2.
84
CIRCULATION RESEARCH
Downloaded from http://circres.ahajournals.org/ by guest on May 8, 2017
level of 30.0 ± 2.9 ml/min to a mean value of 44.4 ± 4.0
ml/min during sympathetic stimulation alone. With concurrent vagal stimulation the mean blood flow decreased
slightly to 41.1 ± 3.5 ml/min. The NE overflow increased
from close to zero to a mean value of 33.2 =t 3.8 ng/min
during sympathetic stimulation alone. The mean reduction
in the rate of NE overflow was 11.2 ± 2.1 ng/min (P <
0.001) during concurrent vagal stimulation.
As shown in the right half of Figure 3, the changes
produced by vagal stimulation all were abolished by atropine. Sympathetic stimulation alone at 2 Hz resulted in a
69.2 =t 17.4% increase in CF. The much greater rise in CF
after atropine probably can be attributed to the absence of
cardiac pacing. The atria and ventricles were paced synchronously before atropine because strong vagal stimulation
would ordinarily produce marked sinus bradycardia and
third-degree atrioventricular block. After atropine, pacing
was no longer necessary. Of greater relevance to the present
study, the reduction in CF ordinarily evoked by concurrent
vagal stimulation was abolished by atropine. Similarly, after
atropine the increase in coronary sinus blood flow evoked by
sympathetic stimulation was unaffected by vagal stimulation. The rate of NE overflow increased after atropine from
near zero to a level of 25.8 ± 5.4 ng/min during sympathetic stimulation. This value was less than that observed
before atropine, although the difference was not significant
statistically (P = 0.3). Concurrent vagal stimulation produced no appreciable reduction in NE overflow (a change of
only 0.2 ± 0.9 ng/min).
Discussion
VOL. 38, No. 2, FEBRUARY
1976
terminals. In the present study, no effort was made to
determine whether the vagally mediated reduction in NE
overflow (Figs. 2 and 3) represents diminished liberation or
enhanced reuptake of this neurotransmitter. However, it has
been shown for the perfused rabbit heart that acetylcholine
does not block the uptake of NE. 26 It is highly probable,
therefore, that the reduced overflow of NE during vagal
stimulation in our experiments reflects diminished release
rather than increased reuptake.
The experiments of Loffelholz and Muscholl which employed vagal stimulation were restricted to atrial tissue;3- *
we have extended their findings to the cardiac ventricles.
In our experiments, only a small fraction of the NE appearing in the coronary sinus blood during sympathetic stimulation originated in the left atrium; the vast majority was derived from ventricular tissue. The atria do receive an abundant sympathetic innervation; per unit of weight, they are
probably more richly innervated than the ventricles. The
myocardial catecholamine concentration is an index of the
density of postganglionic sympathetic terminals,27"30 and it
has been amply demonstrated that the catecholamine concentration in the left atrium is 2 to 3 times as great as that in
the left ventricle.28"31 However, the drainage of venous blood
from the left atrium into the coronary sinus is only a small
fraction of that derived from the left ventricle. In the dog,
the weight of the left atrium is less than 10% of that of the
left ventricle.29 Furthermore, the coronary blood flow to the
left atrium is only about 3% or 4% of the total coronary
blood flow.32-33 A significant fraction of this small flow does
not drain into the coronary sinus, but rather enters the left
atrial cavity through Thebesian channels.34 Hence, most of
the norepinephrine that overflows into the coronary sinus
must be derived from nerve terminals in the ventricular
walls, and only a small fraction is derived from atrial nerve
endings. Therefore, in the present study the changes in NE
overflow caused by vagal stimulation must reflect changes
taking place predominantly in the ventricular walls. Undoubtedly, similar alterations also are occurring in the atrial
walls, but they can account for only a small fraction of the
NE that overflows into the coronary sinus blood.
The vagally induced reduction in ventricular CF observed
in our present study confirms the results of numerous
previous experiments. 10 ' 16 The changes in CF in our study
probably reflect a true negative inotropic vagal effect on the
ventricular myocardium, because most of the other principal
experimental variables that could alter CF were either held
constant or were observed not to change appreciably during
vagal stimulation. Synchronous atrioventricular pacing prevented adventitious changes in ventricular CF in two ways:
(1) it prevented the changes in contractility which are
associated with the force-frequency relationship,23 and (2) it
averted the changes in ventricular preload which are associated with the marked changes in atrial contractility produced by vagal stimulation.13- 24- " The coronary blood flow
during combined vagal and sympathetic stimulation was not
significantly different from that during sympathetic stimulation alone (Fig. 2). Therefore, the vagally induced change in
CF could not be attributed to a concomitant change in
coronary blood flow. Finally, there was no significant
change in arterial blood pressure when vagal stimulation
was superimposed on cardiac sympathetic stimulation.
Hence, the change in CF did not reflect an alteration in
ventricular afterload.
Therefore the reduction in ventricular CF evoked by vagal
stimulation which is shown in this study (Figs. 2 and 3) must
have been caused, at least in part, by a reduction in the rate
of release of NE. The blockade of this effect by atropine
(Fig. 3) supports the contention of Muscholl and his
collaborators2"4-26 that there are muscarinic inhibitory receptors on the terminal sympathetic nerve fibers. The data
we have presented in this paper show that such muscarinic
receptors must be located on the sympathetic terminals in
the walls of the ventricles as well as in other regions of the
heart. Also, the vagal and sympathetic nerve endings must
lie in close enough proximity to each other so that the
acetylcholine released from the vagal endings can combine
with the muscarinic receptors on the sympathetic terminals.
The data obtained in our study support the contention of
Lbffelholz and Muscholl2"4 that the vagally mediated antagonism of the cardiotonic effects of sympathetic stimulation
is accomplished, at least partially, by a reduction in the rate
of release of NE. The overflow of NE into the coronary
sinus reflects the balance between NE release and subsequent reuptake by the sympathetic postganglionic nerve
1. Levy MN: Sympathetic-parasympathetic interactions in the heart. Circ
Res 29: 437-445, 1971
2. Loffelholz K, Muscholl E: A muscarinic inhibition of the noradrenaline
release evoked by postganglionic sympathetic nerve stimulation. Naunyn
Schmiedebergs Arch Pharmacol 265: 1-15. 1969
3. Loffelholz K, Muscholl E: Inhibition by parasympathetic nerve stimula-
References
TRIGGERED MITRAL VALVE ACTIVITY/W// and Cranefield
4.
5.
6.
7.
8.
9.
10.
11.
Downloaded from http://circres.ahajournals.org/ by guest on May 8, 2017
12.
13.
14.
15.
16.
17.
tion of the release of the adrenergic transmitter. Naunyn Schmiedebergs
Arch Pharmacol 267: 181-184, 1970
Muscholl E: Muscarinic inhibition of the norepinephrine release from
peripheral sympathetic fibres. In Pharmacology and the Future of Man:
Proceedings of the 5th International Congress of Pharmacology, vol 4,
edited by FE Bloom, GH Acheson. White Plains, .New York, Albert J.
Phiebig, 1973, pp 440-457
Hollenberg M, Carriere S, Barger AC: Biphasic action of acetylcholine
on ventricular myocardium. Circ Res 16: 527-536, 1965
Dempsey PJ, Cooper T: Ventricular cholinergic receptor systems:
Interaction with adrenergic systems. J Pharmacol Exp Ther 167:
282-290, 1969
La Raia PJ, Sonnenblick EH: Autonomic control of cardiac C-AMP.
Circ Res 28: 377-384, 1971
Lee TP, Kuo JF, Greengard P: Role of muscarinic cholinergic receptors
in regulation of guanosine 3':5'-cyclic monophosphate content in mammalian brain, heart muscle, and intestinal smooth muscle. Proc Natl
Acad Sci (USA) 69: 3287-3291, 1972
George WJ, Wilkerson RD, Kadowitz PJ: Influence of acetylcholine on
contractile force and cyclic nucleotide levels in the isolated perfused rat
heart. J Pharmacol Exp Ther 184: 228-235, 1973
De Geest H, Levy MN, Zieske H, Lipman RI: Depression of ventricular
contractility by stimulation of the vagus nerves. Circ Res 17: 222-235,
1965
Levy MN, Ng M, Martin P, Zieske H: Sympathetic and parasympathetic interactions upon the left ventricle of the dog. Circ Res 19: 5-10,
1966
Pace JB, Randall WC, Wechsler JS, Priola DV: Alterations in ventricular dynamics induced by stimulation of the cervical vagosympathetic
trunk. Am J Physiol 214: 1213-1218, 1968
Harmon MA, Reeves TJ: Effect of efferent vagal stimulation on atrial
and ventricular function. Am J Physiol 215: 1210-1217, 1968
Levy MN, Zieske H: Effect of enhanced contractility on the left
ventricular response to vagus nerve stimulation in dogs. Circ Res 24:
303-311, 1969
Priola DV, Fulton RL: Positive and negative responses of the atria and
ventricles to vagosympathetic stimulation in the isovolumic canine heart.
Circ Res 25: 265-275, 1969
Martin PJ, Levy MN, Zieske H: Analysis and simulation of the left
ventricular response to autonomic nervous activity. Cardiovasc Res 3:
396-410, 1969
Levy MN, Ng ML, Zieske H: Functional distribution of the peripheral
85
cardiac sympathetic pathways. Circ Res 19: 650-661, 1966
18. Anton AH, Sayre DF: A study of the factors affecting the aluminum
oxide-trihydroxyindole procedure for the analysis of catecholamines. J
Pharmacol Exp Ther 138: 360-375, 1962
19. Laverty R, Taylor KM: Fluorometric assay of catecholamines and
related compounds. Anal Biochem 22: 269-279, 1968
20. Siegel JH, Gilmore JP, Sarnoff SJ: Myocardial extraction and production of catechol amines. Circ Res 9: 1336-1350, 1961
21. Hukovic S, Muscholl E: Die Noradrenalin-Abgabe aus dem isolierten
Kaninchenherzen bei sympathischer Nervenreizung und ihre pharmakologische Beeinflussung. Nauyn Schmiedebergs Arch Pharmacol
244:81-96, 1962
22. Yamaguchi N, de Champlain J, Nadeau R: Noradrenaline liberation
from the dog heart in vivo. Can J Physiol Pharmacol 51: 297-305, 1973
23. Koch-Weser J, Blinks JR: The influence of the interval between beats on
myocardial contractility. Pharmacol Rev 15: 601-652, 1963
24. Sarnoff SJ, Brockman SK, Gilmore J P , et al.: Regulation of ventricular
contraction; influence of cardiac sympathetic and vagal nerve stimulation
on atrial and ventricular dynamics. Circ Res 8: 1108-1122, I960
25. Williams JF, Sonnenblick EH, Braunwald E: Determinants of atrial
contractile force in the intact heart. Am J Physiol 209: 1061-1068, 1965
26. Lindmar R, Loffelholz K, Muscholl E: A muscarinic mechanism
inhibiting the release of noradrenaline from peripheral adrenergic nerve
fibres by nicotinic agents. BrJ Pharmacol Chemother 32: 280-294, 1968
27. Hirsch EF, Willman VL, Jellinek M, Cooper T: The terminal innervation
of the heart. Arch Pathol 76: 677-692, 1963
28. Klouda MA: Distribution of catecholamine in the dog heart. Proc Soc
Exp Biol Med 112: 728-729, 1963
29. Angelakos ET: Regional distribution of catecholamines in the dog heart.
Circ Res 16: 39-44, 1965
30. Jellinek M, Kaye MP, Kaiser GC, Cooper T: Effect of cervical
vagosympathectomy on myocardial catecholamine concentration. Am J
Physiol 209: 951-954, 1965
31. Hikosaka H: The effects of stellate ganglionectomy on the distribution,
uptake and storage of noradrenaline in the dog heart. Jap J Pharmacol
16: 157-164, 1966
32. MacLean LD, Hedenstrom PH, Kim YS: Distribution of blood flow to
the canine heart. Proc Soc Exp Biol Med 107: 786-789, 1961
33. Love WD, O'Meallie LP: Clearance of R b " from coronary blood by the
atria of dogs. Proc Soc Exp Biol Med 112: 911-913, 1963
34. Moir TW, Driscol TE, Eckstein RW: Thebesian drainage in the left heart
of the dog. Circ Res 14: 245-249, 1964
Triggered Activity in Cardiac Muscle Fibers of the
Simian Mitral Valve
ANDREW L. WIT, P H . D . , AND PAUL F. CRANEFIELD, M.D.,
PH.D.
S U M M A R Y The action potential of cardiac fibers in the anterior
mitral valve leaflet of the monkey heart is followed by an after-hyperpolarization. The addition of catecholamines causes a delayed
after-depolarization to follow the after-hyperpolarization. The amplitude of the after-depolarization increases as the stimulus cycle length
is decreased, or after premature stimulation, and as a result can reach
threshold to yield nondriven, sustained rhythmic activity which we
term triggered activity. This sustained rhythmic activity can be
terminated by a single, appropriately timed, premature stimulus. The
amplitude of the action potentials of mitral valve fibers is increased
by catecholamines; the amplitude and rate of depolarization are
depressed by verapamil. The amplitude of the action potentials is
little affected by tetrodotoxin (TTX) but the maximum rate of
depolarization is reduced by TTX. The delayed after-depolarization
induced by catecholamines is abolished by verapamil, as is triggered
activity. These observations suggest that mitral valve fibers generate
slow response action potentials, that triggerable sustained rhythmic
activity may be a property of the slow response and that such activity
may cause the types of cardiac arrhythmias that usually are attributed to reentry.
WE HAVE described, in Purkinje fibers exposed to sodiumfree solutions, a form of sustained rhythmic activity that can
be initiated and sometimes terminated by a single stimulus
and that is probably not reentrant. 1 - 2 . The driven action
potential that triggers such activity is followed by an early
after-hyperpolarization and a delayed after-depolarization.
From the Department of Pharmacology, Columbia University College of
Physicians and Surgeons, and The Rockefeller University, New York, New
York.
Supported by U.S. Public Health Service Grants HL-12738-06 and
HL-14899 from the National Heart and Lung Institute.
Dr. Wit was a Senior Investigator of the New York Heart Association
during this study and is a Career Scientist of the Irma T. Hirschl Trust.
Received April 3, 1975; accepted for publication October 13, 1975.
Effect of vagal stimulation on the overflow of norepinephrine into the coronary sinus during
cardiac sympathetic nerve stimulation in the dog.
M N Levy and B Blattberg
Downloaded from http://circres.ahajournals.org/ by guest on May 8, 2017
Circ Res. 1976;38:81-84
doi: 10.1161/01.RES.38.2.81
Circulation Research is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 1976 American Heart Association, Inc. All rights reserved.
Print ISSN: 0009-7330. Online ISSN: 1524-4571
The online version of this article, along with updated information and services, is located on the
World Wide Web at:
http://circres.ahajournals.org/content/38/2/81
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in
Circulation Research can be obtained via RightsLink, a service of the Copyright Clearance Center, not the
Editorial Office. Once the online version of the published article for which permission is being requested is
located, click Request Permissions in the middle column of the Web page under Services. Further information
about this process is available in the Permissions and Rights Question and Answer document.
Reprints: Information about reprints can be found online at:
http://www.lww.com/reprints
Subscriptions: Information about subscribing to Circulation Research is online at:
http://circres.ahajournals.org//subscriptions/