Inhibition of adrenergic outflow to peripheral blood vessels by vagal afferents from the cardiopulmonary region in the dog

In closed chest atropinized dogs anesthetized with chloralose and ventilated artificially, the aortic nerves were cut beneath the nodose ganglion, and the carotid sinuses were either denervated or vascularly isolated and maintained at a pressure of 40 mm Hg. Denervation was established by the failure of the pressoreceptor systems to respond to mechanical stimulation. Cold block or section of the cervical vagi resulted in statistically significant increases in arterial blood pressure (18%), heart rate (3%), central venous pressure (13%), hind limb perfusion pressure (12%), pressure within the occluded spleen (18%), and efferent renal sympathetic nerve activity (28%). There was no change in saphenous vein perfusion pressure. The vascular responses were abolished by α receptor blockade and were not affected by section of the vagi at the diaphragm. When the pressure in the vascularly isolated innervated carotid sinuses was varied from 40 to 220 mm Hg, the vascular responses to vagal block decreased steeply between 100 and 160 mm Hg and were absent at 200 mm Hg. Thus, receptors in the cardiopulmonary region with afferent vagal fibers exert a continuous restraint on the sympathetic adrenergic outflow to resistance and capacitance vessels, especially when the input from the carotid baroreceptors is decreased.