Measurement of Plasma Renin Concentration (PRC) Using Exogenous Substrate and Radioimmunoassay

Abstract. An assay to determine renin concentration (RC) has been developed which allows quantitation on a scale of Goldblatt units (G.U.) and provides a way of comparing results from various laboratories. Renin activity is protected by Cleland's reagent. The enzymatic reaction is standardized for pH (8.0), temperature (30^o C), time (30 min.) and by using hog plasma renin substrate (optimal pH 8.0). The latter avoids the interference of pseudorenin (optimal pH 5.0) and reduces the effects of endogenous renin substrate upon the enzyme reaction. The standard curves were corrected for the blank. Angiotensin I generated was measured by a double antibody radioimmunoassay method. Recoveries of added enzyme provided a control for the assay and were 96±12.5% (SD) for 47 experiments. The coefficient of variation was 16.8% and the sensitivity of the assay (=2 SD) was 0.2×10^-4 G.U. per ml plasma. The effect of various materials on the hydrolysis of hog substrate by renin was studied. Plasma renin concentration (PRC) from healthy individuals on an uncontrolled diet and in the upright position was 0.88 ±0.09 times 10^-4 G.U. per ml. Patients suffering from primary aldosteronism had suppressed values of PRC which reached maximal levels of 0.2 ×10^-4 G.U. per ml in the upright position on a sodium restricted diet (10 mEq per day).