Measurement of urinary renin activity by radioimmunoassay: Sequential studies in acute renal failure in man

Urinary renin activity (URA) was measured by radioimmunoassay in sequential studies of 5 patients with acute renal failure (ARF) and in 13 normal volunteers. URA was elevated during the oliguric phase of ARF and fell to low levels prior to resolution of oliguria. Plasma renin activity (PRA) varied appropriately in response to changes in intravascular volume status. In normal volunteers, the very low URA values did not change following furosemide-induced increases in PRA. A simple, rapid, and accurate method is described for the measurement of URA in humans by radioimmunoassay of angiotensin I generated during incubation of urine with homologous plasma substrate. The urinary enzyme exhibited the same properties as purified renal renin and the incubation product appeared identical to angiotensin I standard. Renin activity in urine was directly proportional to enzyme concentration and no evidence was obtained for interference from other proteolytic activities or from inhibitors or promoters of renin in urine.