Effect of vasopressin antagonist and saralasin on regional blood flow following hemorrhage.

The effects of hemorrhagic hypotension on mean arterial pressure (MAP), cardiac output (CO), and its distribution were investigated in halothane-anesthetized rats using the radioactive microsphere technique. Hemorrhage (12 ml/kg) decreased MAP and CO, increased total peripheral resistance (TPR), and decreased blood flow (BF) to the heart, stomach, intestine, kidneys, skin, cecum, and colon. The effects of antagonists of vasopressin and the renin-angiotensin system on peripheral circulation following hypotensive hemorrhage were also examined using d(CH2)5Tyr(Me)AVP and saralasin, respectively. Injection of the vasopressin antagonist caused a reduction of MAP by reducing TPR and caused an increase of percent distribution of CO to the stomach, skin, cecum, and colon. Intravenous infusion of saralasin caused significant reductions of MAP by reducing TPR. Saralasin caused an increase of percent distribution of CO to the kidneys. The results show that both vasopressin and the renin-angiotensin systems participate in the control of MAP and peripheral vascular resistance following hypotensive hemorrhage in anesthetized rats.