Radioimmunoassay of angiotensin i in human plasma - comparison of two renin activity methods

Plasma renin activity (PRA) was measured by radioimmunoassay of angiotensin I generated during 1 hour incubation at the pH-optimum. Angiotensin I was then assayed directly in the plasma or after extraction on a Dowex resin. A significant (p < 0.001) correlation between the PRA-values obtained with both methods was observed. PRA determined in untreated (r = 0.79, p < 0.001) or extracted (r = 0.87, p < 0.001) plasma samples, was similarly related to simultaneously measured plasma angiotensin II levels. The predictive value of PRA, determined with both methods, in the hypotensive action of saralasin (an angiotensin II antagonist) and of captopril (an orally active angiotensin converting enzyme inhibitor) was of the same magnitude.