Insignificant bilateral convergence of preganglionic vagal fibers on postganglionic neurons to the canine heart.

We determined the extent of convergence of preganglionic fibers from the right and left vagus nerves on postganglionic neurons that supply the sinoatrial node in chloralose-anesthetized dogs. We administered hemicholinium-3 and stimulated the right vagus nerve at a high frequency to deplete acetylcholine from the postganglionic parasympathetic neurons supplied by that nerve. We compared the effects of this "depletion regimen" with the responses in two control groups: a stimulation control group, which was subjected to high-frequency right vagus stimulation only, and a drug control group, which received a hemicholinium-3 infusion only.

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

Glucagon accelerates the heart independent of sympathetic nervous system stimulation. The effect of glucagon on the chronotropic responses to repetitive bursts of vagal stimulation was determined in open-chest anesthesized dogs. When the cervical vagi were stimulated at constant frequencies, the change in heart rate was not affected by glucagon administration, i.

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

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.

Effects of repetitive bursts of vagal activity on atrioventricular junctional rate in dogs.

A stable atrioventricular (AV) junctional rhythm was produced in open-chest dogs by injecting pentobarbital into the sinus node artery. When the cervical vagus nerves were stimulated repetitively, the junctional pacemaker cells tended to become synchronized with the vagal activity. During such synchronization, the junctional rate varied directly rather than inversely with the frequency of vagal stimulation.