The Regulatory Function of the Renin–Angiotensin System during General Anesthesia

Abstract

Variation of plasma renin activity occurred during anesthesia. The recent development of a specific angiotensin II antagonist, saralasin, allowed the delineation of the role of the renin-angiotensin system in blood pressure control during anesthesia. Rats (27) were divided into 4 groups: awake, halothane (1 MAC [minimal anesthetic concentration]), ketamine (125 mg/kg) and fluroxene (1 MAC). Arterial pressure was recorded continuously and plasma renin activity was determined by radioimmunoassay at the end of a 2 h awake control period, after 1 h of anesthesia, and after half an h of saralasin infusion. A similar protocol for enflurance with 1.75 vol% was also followed in 7 anesthetized rats, but renin analysis was not performed. Anesthesia resulted in decreases in mean arterial pressure from 123.0 .+-. 1.3 toor to 95.2 .+-. 2.2 torr for ketamine, 91.6 .+-. 3.9 torr for halothane, 96.9 .+-. 7.9 torr for fluroxene and 84.5 .+-. 3.8 torr for enflurane. Renin activity did not change significantly from control (4.33 .+-. 0.51 ng/ml per h). When saralasin was infused only the rats anesthetized with halothane or enflurane had significant decreases in mean blood pressure to 75.0 .+-. 4.8 and 66.1 .+-. 3.4 torr respectively. The anesthetic agents studied did not cause a detectable increase in plasma renin activity. Through the use of a competitive inhibitor of angiotensin II, a significant role for the maintenance of blood pressure by the renin-angiotensin system during halothane and enflurane anesthesia was demonstrated.