Metabolism and rate of secretion of aldosterone in the bullfrog.

A study of the metabolism of aldosterone in the bullfrog was undertaken to provide a measurable metabolite for the indirect isotope dilution technique for measuring secretory rates. The rate of excretion of labeled aldosterone was considerably slower in the frog than in man and made necessary the collection of excretory products for 5 days to insure reasonably complete recovery of metabolites. The major identifiable metabolite was a tetrahydro derivative subsequently identified as 3beta-hydroxy-5beta-tetrahydroaldosterone. This metabolite was excreted partly in the free form and partly as a glucuronic acid conjugate. The pH 1-hydrolyzable conjugate of aldosterone was not detected. For the measurement of secretory rates, aldosterone-(3)H was injected into the dorsal lymph space and the animal placed in a bath to provide an environment of constant electrolyte composition and intake and a means of collecting excretory products. Urine and bath fluid were collected for 5 days, tetrahydroaldosterone was isolated, and its specific activity determined for the calculation of the aldosterone secretory rate. The rate of secretion of aldosterone in the bullfrog was increased by a tap water bath and by bovine adrenocorticotropic hormone, decreased by a saline bath and by dexamethasone, and unchanged by valine-5-angiotensin amide.