Eggena P, Barrett J D, Hidaka H, Chu C L, Thananopavarn C, Golub M S, Sambhi M P
Circ Res. 1977 Oct;41(4 Suppl 2):34-7. doi: 10.1161/01.res.41.4.34.
Plasma renin substrate, a widely measured parameter of the renin reaction, is quantitated indirectly by the measurement of liberated angiotensin I upon exhaustive incubation of plasma with added renin. To overcome methodological problems of this assay system, we have developed a direct radioimmunoassay for this plasma protein using renin substrate purified from pooled plasma of normotensive subjects as the antigen. Comparison of substrate quantitated by the two assay systems (direct and indirect) indicates a 1:1 correlation with the exception of certain subjects with elevated substrate levels induced by estrogen therapy. To study the possibility of multiple substrate forms, we have made a comparison of substrate quantitated by both radioimmunoassays in conjunction with electrophoresis of plasma on polyacrylamide gel. One major form of substrate with a retardation factor (Rf) = 0.60 was found in normotensive and essential hypertensive subjects which gave a 1:1 correspondence on quantitation by the two methods. In contrast, six of 16 women on oral contraceptives demonstrated three forms of substrate (Rf = 0.16, 0.35, and 0.60) on electrophoresis. Substrate with Rf = 0.16 and 0.35 did not cross-react with the antiserum prepared against substrate from normotensive subjects, implying structural differences in these proteins.
血浆肾素底物是肾素反应中一个广泛测量的参数，通过在血浆中加入肾素进行彻底孵育后测量释放的血管紧张素I来间接定量。为了克服该检测系统的方法学问题，我们使用从正常血压受试者的混合血浆中纯化的肾素底物作为抗原，开发了一种针对这种血浆蛋白的直接放射免疫测定法。两种检测系统（直接法和间接法）对底物的定量比较表明，除了某些因雌激素治疗导致底物水平升高的受试者外，两者呈1:1的相关性。为了研究多种底物形式的可能性，我们将两种放射免疫测定法定量的底物与血浆在聚丙烯酰胺凝胶上的电泳结果进行了比较。在正常血压和原发性高血压受试者中发现了一种主要的底物形式，其阻滞系数（Rf）= 0.60，两种方法对其定量结果呈1:1对应关系。相比之下，16名口服避孕药的女性中有6名在电泳中显示出三种底物形式（Rf = 0.16、0.35和0.60）。Rf = 0.16和0.35的底物与针对正常血压受试者底物制备的抗血清不发生交叉反应，这意味着这些蛋白质在结构上存在差异。
