Increased plasma level of renin in experimental secondary hyperaldosteronism

Renal and peripheral venous plasma was prepared for assay of renin by the technique of Helmer and the formed angiotensin II was assayed for both pressor and steroidogenic activity. Both assays showed higher concentrations of renin in both renal and peripheral venous plasma from dogs with thoracic caval constriction than from normal dogs. The increase in aldosterone and corticosterone secretion by isolated adrenals in response to incubated plasma with its formed angiotensin II was qualitatively similar to that observed for synthetic angiotensin II. Thus, the steroid assay provided evidence that the final product formed for assay was angiotensin II. That the pressor activity in renal vein plasma was referable to a substance of renal origin is indicated by the lower level of activity in peripheral venous than in renal venous plasma and the fall in activity in peripheral venous plasma following nephrectomy. Further evidence for the validity of the assay for renin was obtained from studies of renin substrate. A large excess of renin substrate was found in normal dog plasma so that angiotensin II formed by incubation was not limited by substrate exhaustion. Also, the peripheral plasma level of renin substrate was essentially the same in dogs with thoracic caval constriction and in normal dogs.