A New Direct Radioimmunoassay for Human Renin Substrate and Heterogeneity of Human Renin Substrate in Pathological States

Abstract

The presence or absence of correlation in quantitation of human renin substrate by conventional indirect method (equivalent generated angiotensin I; AI) and newly-developed direct radioimmunoassay (immunoassayable substrate) has allowed us to screen heterogeneity of renin substrate in various pathological states, in conjunction with several procedures for protein analysis. One major peak of substrate activity on polyacrylamide gel electrophoresis (PAGE) was found in normotensive and benign essential hypertensive subjects who gave a 1:1 correspondence and a good correlation between two substrate assays. In contrast, certain subjects on estrogen therapy, pregnant woman during the last trimester and some uremic patients demonstrated at least 3 different forms of renin substrate on electrophoresis (Rf of I = 0.65, II = 0.35, III = 0.16). Further analysis by isoelectric focusing PAGE presented additional findings on altered substrate type in patient with Cushing's syndrome (Ip = 4.7 and 4.3). In these additional forms of renin substrate, structural or immunological difference was demonstrated by a lack of binding affinity to antiserum prepared against renin substrate from normotensive subjects. Preliminary data on their AI generation rates in the in vitro incubation with added renin, implied altered kinetic characteristics in the in vivo renin-substrate reaction. These findings confirm the existence of multiple forms of human renin substrate, which physico-chemical and enzymological properties differ from each other. It is suggested that such proteins may be involved in abnormalities of renin-angiotensin system inducing hypertensive states. © 1980, The Japanese Circulation Society. All rights reserved.