REFLEX VASCULAR-RESPONSES TO ABDOMINAL VENOUS DISTENSION IN THE ANESTHETIZED DOG

This study was undertaken to determine whether distension of the subdi aphragmatic veins results in reflex vasoconstriction and interacts wit h the carotid baroreflex. In alpha-chloralose-anesthetized open-chest dogs, a perfusion circuit-controlled carotid sinus and thoracic aortic pressures, splanchnic and limb blood flows, and cardiopulmonary blood flows. At carotid sinus pressures below similar to 90 mmHg, increases in splanchnic venous pressure of 7 mmHg or more resulted in increases in vascular resistance in both the splanchnic and limb circulations; there was no response at higher carotid pressures. At high venous pres sures,the average maximum gains of the carotid baroreflex for splanchn ic and limb resistance responses were increased by 106 and 67%, respec tively. The responses were not abolished by cutting the vagal or phren ic nerves but were prevented by cutting the splanchnic nerves and, for the limb, the sciatic and femoral nerves. These results suggest that splanchnic congestion, by causing vasoconstriction and augmentation of the carotid baroreflex, may be important in the maintenance of blood pressure during gravitational stress.