Inhibition by angiotensin II of baroreceptor‐evoked activity in cardiac vagal efferent nerves in the dog.

Abstract

Action potentials were recorded in single baroreceptor fibers dissected from the carotid sinus nerves in dogs during increases in blood pressure caused by i.v. injection of angiotensin II, and by i.v. injection of phenylephrine or inflation of an aortic balloon. Action potentials were recorded in single cardiac efferent fibers dissected from the right cervical vagus nerve in other dogs during increases in blood pressure caused by angiotensin II and by phenylephrine or by inflation of an aortic balloon. There was no difference in the discharge frequency of single carotid sinus baroreceptor fibers at any blood pressure when phenylephrine, balloon inflation or angiotensin II were used to raise the pressure. Activity in single cardiac vagal efferent fibers was increased when blood pressure was increased by phenylephrine or by inflation of an aortic balloon. When blood pressure rose by a comparable amount in response to angiotensin II, vagal firing decreased (3 fibers), was little changed from control levels (4 fibers), or increased less than it did in response to phenylephrine (1 fiber). While angiotensin II has no effect on baroreceptor sensitivity, it does inhibit vagal discharge which is evoked by stimulation of arterial baroreceptors.