AJP - Heart and Circulatory Physiology, Vol 243, Issue 4 607-H613, Copyright © 1982 by American Physiological Society
Inhibition of baroreflex bradycardia by aortic nerve excitatory afferents in dogs
T. E. Pisarri, G. L. Matson and J. E. Kendrick
In dogs anesthetized with morphine-chloralose, low-frequency high-intensity
stimulation of the aortic nerve (AN) causes a modest reflex tachycardia and
a rise in systemic pressure. Stimulation of the carotid sinus nerve or
raising pressure in the isolated carotid sinus causes reflex bradycardia
and a fall in systemic pressure. Combined stimulation of these reflexes
resulted in less bradycardia and a smaller decrease in systemic pressure
than the sum of the responses to separate stimulation (P less than 0.001).
This suggests that the opposing reflexes interact in a manner whereby the
carotid baroreflex responses are inhibited by the AN stimulation. This
interaction occurs in the medullary centers and appears to involve
primarily suppression of the vagal efferents to the heart. Baroreflex
inhibition of sympathetic vasomotor activity also appears to be suppressed
by AN stimulation. It is concluded that aortic cardiac sympathetic activity
and in part by suppressing baroreflex-induced bradycardia.
