Time course of mesenteric vasodilatation following hypophysectomy and the stopping of a vasopressin infusion.

Hypophysectomy caused an increase in superior mesenteric arterial conductance that reached a new plateau approximately 20 min after removal of the gland in four pentobarbital-anesthetized cats. Intravenous infusion of arginine vasopressin (0.74 +/- 0.21 mU min-1kg-1) caused conductance to decrease to approximately prehypophysectomy control values. Stopping the infusion resulted in an increase in conductance and the time course of this vasodilatation was virtually identical to that which occurred following hypophysectomy. The results are consistent with the interpretation that the effects of acute hypophysectomy on the mesenteric resistance vessels are due primarily to removal of the vasopressin system and the concomitant elimination of circulating vasopressin.