Acute hemorrhage reduces angiotensin converting enzyme activity in conscious sheep

When levels of plasma angiotensin converting activity (ACE) were measured in 11 sheep undergoing a 15 ml/kg hemorrhage, levels before hemorrhage (5.7 +/- 0.5 nmol/min/ml) fell significantly at 120 min (3.7 +/- 0.6 nmol/min/ml) and 150 min (3.4 +/- 0.5 nmol/min/ml) after hemorrhage (P less than 0.01). Plasma ACE activity remained constant in ten control sheep studied under the same conditions but not hemorrhaged. The time course of the fall in plasma ACE activity was then studied in an additional four sheep undergoing 15 ml/kg hemorrhage, which reduced mean arterial pressure by 25% at 10 min after hemorrhage. Plasma ACE activity was variable for 60 min post-hemorrhage, but then fell to levels significantly lower than baseline values at 150 min (P less than 0.05). The decrease in plasma ACE activity associated with hemorrhage was small when compared to the effect of an IV infusion of the ACE inhibitor, Captopril (SQ14225, 28 micrograms/min for 3 hr), which reduced plasma ACE activity in the same sheep to almost undetectable levels. These results show that hemorrhage significantly reduces plasma ACE activity in sheep. However, this effect is small and is unlikely to affect the production of plasma AII following acute hemorrhage.