Vasopressin and angiotensin: reciprocal mechanisms controlling mesenteric conductance

Intravenous infusions of [Sar1-Ala8]angiotensin II, acute hypophysectomy, and acute intestinal denervation were carried out in 15 pentobarbital-anesthetized cats. Infusion of the angiotensin II antagonist caused only a small increase in superior mesenteric arterial conductance and a small decrease in arterial pressure in intact animals, but the changes were subypophysectomy alone caused only a small intestinal vasodilatation and little change in arterial pressure. However, the responses to hypophysectomy were much larger when the gland was removed during a prolonged infusion of the angiotensin II antagonist. Intestinal denervation caused only minor changes in mesenteric conductance and arterial pressure, and the responses to [Sar1-Ala8]angiotensin II and hypophysectomy were largely unaltered by the presence or absence of the intestinal innervation. The results suggest that the renin-angiotensin and vasopressin systems are reciprocal overlapping mechanisms that exert a significant vasoconstrictor influence on the intestinal resistance vessels in the anesthetized cat. In the absence of one control system, the other appears to compensate to maintain resistance.