AJP - Heart and Circulatory Physiology, Vol 235, Issue 6 759-H766, Copyright © 1978 by American Physiological Society
Reflex circulatory changes due to the afferent stimulation of cat pericoronary nerve
T. Shimizu, D. F. Peterson and V. S. Bishop
Two different types of circulatory reflexes evoked by electrical
stimulation of afferent fibers in the left pericoronary nerves were studied
in anesthetized cats. A depressor response (-32.5 mmHg) with bradycardia
(-48.7 beats/min) in 21 of 31 cats was mediated by the C fibers in the
right vagal cardiac nerve trunk. The efferent pathway for the bradycardia
was in caudal cardiac branches of the right vagus. Neither sympathetic
denervation to the heart nor atropine attenuated the hypotensive response
significantly, suggesting that the depressor response results from reflex
inhibition of peripheral sympathetic activity. A pressor reflex without
heart rate change was observed either when the vagi were blocked or when
the distribution of vagal afferents in the pericoronary nerve was
considered to be small. The pressor reflex was mainly mediated by the
afferent C fibers within the left cardiac sympathetic nerves. The depressor
response was enhanced by sympathectomy, suggesting the sympathetic
counteraction on the inhibitory vagal afferents, Similarly, an enhancement
of the pressor reflex by vagal blockade was observed, indicating tonic
vagal restraint on excitatory sympathetic reflexes.
