Hemodynamic reflex in muscle in response to brief occlusion of the mesenteric artery

Brief occlusion of the superior mesenteric artery in the cat produces increases in systemic pressure and in muscle blood flow. Capillary filtration in muscle, measured during occlusion of the superior mesenteric artery, exceeds that of the controls. Propranolol, which blocks the evoked increase in muscle blood flow, reduces capillary filtration during occlusion to less than the control. Cutting the mesenteric nerve returns capillary filtration to the control level. Passive redistribution of blood, such as might follow occlusion of a large vascular region, is not the basis for the evoked changes in muscle hemodynamics. They are abolished by cutting the mesenteric nerve and by propranolol, and are demonstrable during constant pressure perfusion of muscle. The evidence suggests that occlusion of the mesenteric artery produces an increase in capillary filtration by balancing a reflex sympathetic beta-adrenergic vasodilation in pre-capillary resistance vessels with an increase in resistance in the precapillary sphincters.