Effects of calcium channel antagonists on the vagally mediated cardiac chronotropic response in dogs

1990 ◽  
Vol 68 (10) ◽  
pp. 1363-1367 ◽  
Author(s):  
Don W. Wallick ◽  
Sherry L. Stuesse ◽  
Paul Martin
Keyword(s):  
Electrical Stimulation ◽  
Vagus Nerve ◽  
Calcium Channel ◽  
Total Dose ◽  
Cycle Length ◽  
Cardiac Cycle ◽  
Vagal Stimulation ◽  
Calcium Channel Antagonists ◽  
Chronotropic Response ◽  
Stimulation Of

A brief electrical stimulation of the vagus nerve may elicit a triphasic response comprising (i) an initial prolongation of the same or the next cardiac cycle, (ii) a return of the subsequent cardiac cycle to about the level prior to vagal stimulation, and (iii) a secondary prolongation of cardiac cycle length that lasts several beats. We compared the effects of two calcium channel antagonists, verapamil and nifedipine, on this triphasic response to vagal stimulation in chloralose-anesthetized, open-chest dogs. In the absence of vagal stimulation, nifedipine (doses of 10, 40, and 50 μg/kg for a total dose of 100 μg/kg, i.v.) and verapamil (two doses of 100 μg/kg each, i.v.) increased the cardiac cycle length (A–A interval) by 16% (429 ± 20 to 496 ± 21 ms) and 29% (470 ± 33 to 605 ± 54 ms), respectively. Nifedipine (100 μg/kg total) attenuated the initial vagally mediated prolongation of the A–A interval, from 474 ± 19 to 369 ± 42 ms above the basal A–A interval. Following the initial prolongation of the vagal effect, other A–A intervals were not affected. In contrast, verapamil potentiated the vagally mediated initial prolongation in cardiac cycle length at the first dose administered (100 μg/kg) from 492 ± 17 to 561 ± 14 ms, but other increases in dosages had no further effect. Thus these two calcium channel antagonists have different effects on the sinoatrial chronotropic responses caused by brief vagal stimulation.Key words: autonomic control, parasympathetic, heart, calcium.

Verapamil potentiates vagally mediated sinoatrial chronotropic responses in dogs

1986 ◽  
Vol 64 (7) ◽  
pp. 954-957
Author(s):  
Don W. Wallick ◽  
Sherry L. Stuesse ◽  
Frank Valencic ◽  
Richard B. Fratianne
Keyword(s):  
Vagus Nerve ◽  
Cycle Length ◽  
Cardiac Cycle ◽  
Sinoatrial Node ◽  
Vagal Stimulation ◽  
Blocking Agent ◽  
Chronotropic Response ◽  
Channel Blocking ◽  
Initial Action ◽  
Electrical Stimuli

A brief burst of electrical stimuli delivered to the vagus nerve during the cardiac cycle elicits a triphasic cardiac chronotropic response. The cardiac cycle length initially increases, then briefly decreases, and subsequently increases again. We studied the effects of a calcium channel blocking agent, verapamil, on these responses to vagal stimulation during sinoatrial nodal rhythm in anesthetized, open-chest dogs. Verapamil increased the basal cardiac cycle length only slightly; however, the primary cardioinhibition was accentuated approximately 40% (from 396 to 555 ms) by verapamil. Neither the acceleratory phase of this triphasic response nor the secondary cardioinhibition was significantly affected by verapamil. These results indicate that verapamil potentiates the initial action of acetylcholine at the sinoatrial node when the vagus is activated with brief stimuli.

Effects of digoxin on the chronotropic responses to repetitive vagal stimules bursts in the dog

1984 ◽  
Vol 62 (11) ◽  
pp. 1411-1415 ◽  
Author(s):  
Daniel G. Pace ◽  
Yukitaka Masuda ◽  
Isaac Eisenstein ◽  
Matthew N. Levy
Keyword(s):  
Vagus Nerve ◽  
Cumulative Dose ◽  
Cardiac Cycle ◽  
Vagal Stimulation ◽  
Cardiac Pacemaker ◽  
Pacemaker Cells ◽  
Chronotropic Response ◽  
Cycle Lengths ◽  
Anesthetized Dogs

We studied the effects of digoxin on the chronotropic responses of the heart to repetitive bursts of vagal stimulation in chloralose-anesthetized dogs. The frequency of the stimulus bursts was increased linearly with time. Over a certain range of frequencies, the cardiac pacemaker became synchronized with the vagal stimulation in a 1:1 ratio of heart beats to stimulus bursts. Digoxin increased the range of cardiac cycle lengths over which 1:1 synchronization occurred during repetitive vagal stimulation. This increment in the range of synchronization varied directly with the dose of digoxin. Before digoxin was given, the range of cardiac cycle lengths over which synchronization occurred when the vagus nerve was stimulated with 10 pulses per burst was 272 ± 50 (mean ± SE) ms. However, after a cumulative dose of 120 μg/kg−1 digoxin had been given, the range of 1:1 synchronization increased to 396 ± 32 ms. Digoxin did not appear to have a proportionately greater effect on those processes that take place in the phase of the cardiac cycle during which the pacemaker cells are maximally responsive than on those processes that occur in the phase of the cycle during which the pacemaker cells are minimally responsive. Therefore, we conclude that the augmented entrainment induced by digoxin is ascribable to its tendency to enhance the chronotropic response to vagal stimulation.

Sustained increases in heart rate induced by timed repetition of vagal stimulation in dogs

1985 ◽  
Vol 249 (4) ◽  
pp. H703-H709
Author(s):  
T. Yang ◽  
M. D. Jacobstein ◽  
M. N. Levy
Keyword(s):  
Cycle Length ◽  
Cardiac Cycle ◽  
Vagal Stimulation ◽  
Sinus Node ◽  
Critical Time ◽  
Critical Value ◽  
Chronotropic Effect ◽  
Chronotropic Response ◽  
The Right ◽  
Positive Chronotropic Effect

We determined the influence of the "free-running cycle length" (tau FR) on chronotropic responses to one burst of right vagal stimuli per cardiac cycle in anesthetized dogs (tau FR, cycle length that prevailed in absence of right vagal stimulation). We varied tau FR by the following methods: 1) tonic left vagal stimulation in pentobarbital-anesthetized animals; 2) tonic left vagal stimulation plus sinus node cooling in pentobarbital-anesthetized animals; and 3) anesthesia with fentanyl, droperidol, and pentobarbital. When tau FR was less than a critical value [1,019 +/- 60 (SE) ms], right vagal stimulus bursts always had the expected negative chronotropic effect. However, when the tau FR was increased beyond critical value, right vagal stimulus bursts delivered within a specific portion of cardiac cycle actually had a positive chronotropic effect; i.e., cycle lengths diminished to values below tau FR. As tau FR was progressively increased beyond critical value, positive chronotropic response became greater and could be evoked by stimulus bursts delivered within a greater fraction of cardiac cycle. The right vagal stimuli that elicited the maximum positive chronotropic effect were those that were given approximately 235 ms prior to beginning of next atrial depolarization. This critical time probably occurs near the end of the period of phase 4 depolarization of sinus node automatic cells.

Vasopressin secretion after stimulation of abdominal vagus in rabbit: role of A1 norepinephrine neurons

1994 ◽  
Vol 266 (6) ◽  
pp. R1885-R1890 ◽  
Author(s):  
Z. J. Gieroba ◽  
W. W. Blessing
Keyword(s):  
Electrical Stimulation ◽  
Vagus Nerve ◽  
Medulla Oblongata ◽  
Vagal Stimulation ◽  
Vagal Afferents ◽  
Neuronal Function ◽  
Plasma Vasopressin ◽  
Vasopressin Secretion ◽  
Stimulation Of

We determined whether electrical stimulation of the abdominal vagus nerve causes secretion of vasopressin in the rabbit and whether inhibition of neuronal function in the A1 region of the medulla oblongata impairs this secretion. In urethan-anesthetized rabbits, electrical stimulation of the abdominal vagus (5-min train of cathodal pulses, 0.5 ms duration, 20 Hz, 0.5-1 mA) increased plasma vasopressin from 37 +/- 8 to 133 +/- 19 pg/ml (P < 0.01, n = 11). Prior section of the cervical vagus completely prevented the increase seen with stimulation of the abdominal vagus. Injecting the inhibitory agent muscimol (1 nmol) 2 mm dorsal to the A1 area did not significantly reduce the vasopressin response to abdominal vagal stimulation. However, when muscimol was injected into the A1 area, the vagally mediated increase in plasma vasopressin was completely prevented. Our results show that stimulation of abdominal vagal afferents causes secretion of vasopressin in the rabbit via a central pathway that includes neurons in the A1 area.

Effects of catecholamines on cardiac chronotropic response to vagal stimulation in the dog

1983 ◽  
Vol 245 (5) ◽  
pp. H721-H724 ◽  
Author(s):  
C. Chassaing ◽  
P. Duchene-Marullaz ◽  
M. J. Veyrac
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Vagus Nerve ◽  
Neurotransmitter Release ◽  
Acetylcholine Release ◽  
Vagal Stimulation ◽  
Norepinephrine Release ◽  
Chronotropic Response ◽  
Anesthetized Dogs ◽  
Stimulation Of

The influence of isoproterenol, norepinephrine, and dopamine on the cardiomoderator effects of moderate vagal stimulation was studied in anesthetized dogs. The drugs were administered at increasing doses in successive perfusions. Stimulation of the vagus nerve, the parameters of which remained constant throughout each experiment, was performed immediately before each sequence of perfusion and after 10-min perfusion. Isoproterenol at 0.025, 0.05, 0.1, and 0.2 microgram X kg-1 X min-1 raised heart rate dose relatedly but did not alter heart rate under vagal stimulation. Thus the amplitude of vagal bradycardic effects increased dose relatedly. Norepinephrine at 0.125, 0.25, 0.5, and 1 microgram X kg-1 X min-1 lowered heart rate through reflex hypertension. Heart rate under vagal stimulation remained constant. Thus the effects of vagal stimulation decreased as dose increased, finally becoming null. Dopamine at 0.5, 1, 2.5, and 5 micrograms X kg-1 X min-1 did not significantly alter heart rate, but at 10 and 20 micrograms X kg-1 X min-1, like norepinephrine, it raised blood pressure, causing a reflex fall in heart rate. At all doses, heart rate under vagal stimulation remained stable. Consequently, at the highest doses, the net effects of vagal stimulation were slight. These results suggest the simultaneous involvement of sympathetic-parasympathetic interactions both post- and prejunctionally. In the latter case, different mechanisms of regulation of neurotransmitter release are involved during vagal stimulation according to the sympathomimetic used. With isoproterenol, norepinephrine release seems more particularly affected, whereas with norepinephrine and dopamine, acetylcholine release is apparently inhibited.

Changes in vagal phasic chronotropic responses with sympathetic stimulation in the dog

1981 ◽  
Vol 241 (6) ◽  
pp. H850-H856 ◽  
Author(s):  
S. L. Stuesse ◽  
D. W. Wallick ◽  
H. Zieske ◽  
M. N. Levy
Keyword(s):  
Cycle Length ◽  
Temporal Relationship ◽  
Cardiac Cycle ◽  
Vagal Stimulation ◽  
Cardiac Response ◽  
Sympathetic Stimulation ◽  
Pacemaker Cells ◽  
Paradoxical Response ◽  
Chronotropic Response ◽  
Anesthetized Dogs

Sympathetic stimulation both shortens the cardiac cycle and potentiates the cardiac response to vagal stimulation. In the present study the effects of sympathetic stimulation on the chronotropic responses of the heart to brief bursts of vagal stimulation were determined in open-chest anesthetized dogs. The sinoatrial nodal pacemaker cells demonstrate a paradoxical response to repetitive bursts of vagal stimuli over a certain portion of the cardiac cycle. That is, the cardiac cycle length does not increase but actually decreases as the vagal stimulation frequency is raised. Background levels of sympathetic stimulation do not significantly alter the range over which this “paradoxical” response occurs. Sympathetic stimulation decreases the cardiac chronotropic response to short bursts of vagal stimuli regardless of the time in the cardiac cycle that the stimulus is given; however, it does not decrease the time from the minimum vagal chronotropic response to the subsequent atrial depolarization although the total cardiac cycle is shortened. Since sympathetic stimulation shifts the overall temporal relationship between vagal stimulation and pacemaker response, small changes in sympathetic tone may greatly alter the cardiac response to phasic vagal stimulation if the vagal stimulus is given at certain times in the cardiac cycle.

Electrical Stimulation of the Vagus Nerve Modulates the Development of Oxygen Epilepsy in Rabbits

2017 ◽  
Vol 47 (3) ◽  
pp. 345-351
Author(s):  
S. Yu. Zhilyaev ◽  
A. N. Moskvin ◽  
T. F. Platonova ◽  
I. T. Demchenko
Keyword(s):  
Electrical Stimulation ◽  
Vagus Nerve ◽  
Stimulation Of

Prolonged Apnea, Vagal Overactivity, and Sudden Infant Death

PEDIATRICS ◽  
1973 ◽  
Vol 51 (4) ◽  
pp. 755-755
Author(s):  
David S. Bachman
Keyword(s):  
At Risk ◽  
Vagus Nerve ◽  
Sudden Infant Death Syndrome ◽  
Infant Death ◽  
Vagal Stimulation ◽  
Sudden Infant Death ◽  
Sudden Infant ◽  
Prolonged Apnea ◽  
Stimulation Of

The article on prolonged apnea and the sudden infant death syndrome (SIDS) by Steinschneider1 is very exciting in that it suggests the possibility of identifying infants at risk from SIDS before the final event. Obviously, it is of great importance to learn the mechanism causing the preceding apneic episodes. Do they represent vagal overactivity? Stimulation of the intact vagus nerve in the unanesthetized monkey causes apnea, as well as bradycardia and even arrhythmias.2 In fact, we have seen myocardial myocytolysis secondary to vagal stimulation.3

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