Occlusive summation of carotid and aortic baroreflexes in control of renal nerve activity.

We recently reported that denervation of aortic or carotid baroreceptors impaired baroreflex control of heart rate but not of hindlimb vascular resistance or lumbar sympathetic nerve activity. Since baroreflex control of sympathetic outflow to different vascular beds is nonuniform, we determined whether carotid or aortic baroreceptor denervation would impair baroreflex control of renal nerve activity. Experiments were performed in 23 alpha-chloralose-anesthetized rabbits. Phenylephrine and nitroglycerin were infused to raise or lower arterial pressure. Pressure elevation inhibited and pressure reduction increased renal nerve activity. The linear regression relationships between changes in arterial pressure and percent change in renal nerve activity were determined with baroreflexes intact and after aortic or carotid denervation. Neither carotid nor aortic denervation alone impaired baroreflex control of renal nerve activity. In nine experiments responses were determined first with vagi sectioned. The results were comparable to those obtained without prior vagotomy. Our data indicate that one group of baroreceptors (aortic or carotid) exerts full control of renal nerve activity and that aortic and carotid baroreflex influences on renal nerve activity add by occlusive or mutual inhibitory summation.