A simple microassay for the estimation of renin concentration in plasma.

A simple assay for the measurement of renin concentration and renin substrate concentration in microliter quantities of rat plasma is described. In the plasma renin concentration assay 5 microliter of rat plasma was incubated for 2 hr at 37 degrees C in the presence of 20 microliter renin substrate (plasma from nephrectomized rats) and 5 microliter inhibitor-buffer solution pH 7.4. At the end of the enzymic incubation the generated angiotensin I was estimated by radioimmunoassay. Angiotensin I antisera and iodinated angiotensin I were added to the same tube and left to equilibrate at 45 degrees C for 15 hr. EDTA, dimercaprol, and 8-hydroxyquinoline were used to inhibit converting enzymes and angiotensinases. Reproducibility of the assay was good, and recovery of added angiotensin I complete. The normal range of plasma renin in rats was between 7 and 15 pmol angiotensin l/ml/hr.