Arterial pressure regulation during hemorrhage: homeostatic role of angiotensin II.

The role of the renin-angiotensin system in the maintenance of arterial pressure following hemorrhage was studied in conscious dogs. Hemorrhage (20 ml/kg body wt) decreased the mean arterial pressure, but compensatory mechanisms partially restored the arterial pressure toward normal. Plasma renin activity increased more than twofold following hemorrhage. To evaluate the role of endogenous angiotensin II in this compensatory response, a specific competitive antagonist of angiotensin II, 1-sarcosine-8-alanine-angiotensin II, was infused intravenously at 6.0 mug/kg min-1 for 30 min; the mean posthemorrhage arterial pressure decreased from 102 plus or minus 7 mmHg to 80 plus or minus 6 mmHg after 15 and 30 min of analog infusion (P less than 0.01 for both values). After a recovery period of 60 min, arterial pressure returned to pre-infusion levels. These results suggest that angiotensin II plays an important role in the short-term maintenance of arterial pressure following hemorrhage in the conscious animal.