Pressor Reflexes Produced by Stimulation of Afferent Fibers in the Cardiac Sympathetic Nerves of the Cat

Abstract

Afferent fibers in cardiac sympathetic nerves were stimulated electrically in an attempt to evoke circulatory reflexes. A pressor response was always elicited during stimulation of the central end of the cut left inferior cardiac or pericoronary nerve in vagotomized intact-brain or spinal cats. The maximum blood pressure rise was 21.5 mm Hg during inferior cardiac nerve stimulation and 14.1 mm Hg during pericoronary nerve stimulation. Heart rate and respiration were unaffected by stimulation. The alpha-receptor-blocking agent phenoxybenzamine hydrochloride abolished the pressor response. Sequential sectioning of cardiac nerves arising from either the stellate ganglion or the thoracic sympathetic trunk, or of white rami 1 through 4, indicated that each branch carried afferents contributing to the pressor response. Evoked potentials revealed that excitation of Aδ fibers in the inferior cardiac nerve elicited a weak pressor response, and excitation of C fibers provoked a much stronger response. C fiber continuity between the pericoronary nerve and the inferior cardiac nerve was demonstrated.