Reflex circulatory changes due to the afferent stimulation of cat pericoronary nerve

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.