A simple solid phase radioimmunoassay for plasma renin activity (author's transl)

Abstract

A solid phase radioimmunoassay (RIA) in which plasma renin activity (PRA) can be measured in a single test tube throughout enzymatic reaction and determination of angiotensin-I (A-I) generated was developed. Two hundred micro 1 of plasma samples was incubated with phenylmethylsulfonyl fluoride (PMSF) and ethylenediamine tetraaceticacid (EDTA) at pH 6.0 or 7.4 at 37 degrees C for 1 hr, then the generated A-I was determined by solid phase RIA under 3 hr of incubation time at room temperature. An antibody absorbed onto polystyrene beads was used for B/F separation of RIA. The combination of PMSF and EDTA gave significant inhibition of angiotensinase and converting enzyme. Pepstatin A, proteolytic enzyme inhibitor, was found to be effective to block the renin activity during the incubation for RIA at room temperature. Recoveries of A-I added at two levels of 1.0 4.0 ng/ml to plasma sample incubated at 37 degrees C for 1 hr were 102 +/- 28.6% and 105 +/- 15.2%, respectively. Intra-assay precision (CV) ranged from 2.5 to 10.3% and inter-assay from 7.0 to 13.7% with four pooled sera. PRA obtained under enzymatic reaction of pH 6.0 showed approximately twice as much as that of pH 7.4. The assay correlated closely with the other established solid phase radioimmunoassay kit (r = 0.996). Normal values of PRA were 1.03 +/0 0.78 ng/mg/hr (n = 66) at supine position and 1.33 +/- 1.15 ng/ml/hr at upright position. The method for the measurement of PRA, described in this paper, can be clinically used as one of convenient methods froms its simplicity and reproducibility.