Abstract
1. Plasma renin concentration was higher in pregnant rats than in non-pregnant female controls (43 +/- 5 vs. 12 +/- 1 ng/ml. per hr); 24 hr post partum, it was 8 +/- 2 ng/ml. per hr. 2. Twenty-four hours after bilateral nephrectomy, plasma renin concentrations in pregnant and non-pregnant rats were not significantly different from zero; the uterine venous minus arterial value in nephrectomized pregnant rts was not significantly different from zero either, and was not increased by haemorrhage. These observations suggest that neither the pregnant uterus nor any other extrarenal site of renin storage contributes to the elevated plasma renin concentration. 3. The disappearance of plasma renin following bilateral nephrectomy was resolved into fast and slow components. The half-time of the slow component, which is considered to reflect the metabolic clearance of renin was significantly higher in pregnant rats than in controls. It is concluded that the plasma renin concentration is elevated, at least in part, because of a decreased metabolic clearance of renin during pregnancy.