Reflex responses of abdominal vascular capacitance from aortic baroreceptors in dogs.

The vascularly isolated abdominal circulation of chloralose-anesthetized dogs was perfused at constant flow through the aorta and drained at constant pressure from the inferior vena cava. Changes in resistance were calculated from changes in perfusion pressure and changes in capacitance were calculated by integrating changes in venous outflow. While carotid sinus pressure was constant, a decrease in pressure in the vascularly isolated aortic arch, over the whole range of baroreceptor sensitivity, decreased abdominal vascular capacitance by 2.9 ml-kg-1 (mean, SE +/- 0.42) and increased the abdominal vascular resistance by 35 +/- 7.1%. Decreases in pressure in the vascularly isolated carotid sinuses, while aortic pressure was constant, decreased capacitance by 5.0 +/- 0.62 ml-kg-1 and increased resistance by 72 +/- 15.9%. Responses of capacitance and resistance to changes in aortic pressure were greatest when carotid pressure was held near threshold levels and least when it was held at levels that would maximally excite carotid baroreceptors. The responses to changes in aortic pressure were abolished when the venous nerves were cooled or the splanchnic nerves were cut.