INVITRO STUDY OF FROG (RANA-RIDIBUNDA PALLAS) INTERRENAL FUNCTION BY USE OF A SIMPLIFIED PERIFUSION SYSTEM .2. INFLUENCE OF ADRENOCORTICOTROPIN UPON ALDOSTERONE PRODUCTION

In order to investigate various factors capable of regulating frog adrenal steroidogenesis, Rana ridibunda adrenal fragments were continuously perifused for 10 hr with amphibian culture medium (ACM). Aldosterone concentrations in the effluent medium were assayed without prior extraction by means of a sensitive and highly specific radioimmunoassay method. In all the experiments, large amounts of aldosterone were secreted even in the absence of ACTH stimulation. Aldosterone output paralleled temperature variations (5 to 30°). A highly significant correlation (r = 0.982; P < 0.01) was established between the outputs of corticosterone and aldosterone during this experiment. Infusion of frog distal lobe extract gave a dose-related response, with the highest dose (0.08 distal lobe eq/ml) yielding a 6.7-fold increase in aldosterone output. In this experiment, interrenal tissue produced two times as much aldosterone as corticosterone. When various dilutions of frog intermediate lobe extracts were tested upon interrenal fragments, a linear log-dose response in aldosterone production was observed for the lower doses and a plateau was reached for the higher doses (0.05 and 0.1 intermediate lobe eq/ml). Dibutyryl cyclic AMP, at a dose of 10 mM, led to a 3.18-fold increase in aldosterone output. These results suggest that aldosterone secretion is controlled by ambient temperature and by circulating levels of adrenocorticotropin. They demonstrate that, in frogs, output of aldosterone is two times higher than output of corticosterone. The aldosterone-corticosterone ratio is even larger after stimulation by high doses of ACTH. Finally, they confirm the presence of large concentrations of biologically active corticotropin in the intermediate lobe of frog pituitary. © 1979.