Role of aortic and vagus nerves in arterial baroreflex bradycardia in rabbits

Abstract

The mechanism that eventually restores heart rate to normal during continuous arterial baroreceptor stimulation is not known. One step toward an understanding of this mechanism was to assess the relative contribution of afferent and efferent nerve pathways to the initial reflex bradycardia elicited by a rise of arterial pressure. The amount of reflex slowing at the end of a 10-min infusion of angiotensin into conscious rabbits was studied before and after sectioning vagus or aortic nerves. A 20–30 mm Hg rise in arterial pressure caused an average decrease in heart rate of 23% in control rabbits, 10% in aortic denervated, 3% in vagus denervated, and 9% after atropine block. These results indicate that the major contribution from afferent pathways to cardiac reflex slowing is through aortic nerves rather than carotid sinus or other afferent nerves. On the efferent side, vagus nerves have more effect on cardiac slowing than does sympathetic nerve inhibition.