IN-VITRO STUDY OF THE EFFECT OF UROTENSIN-II ON CORTICOSTEROID SECRETION IN THE FROG RANA-RIDIBUNDA

Urotensin II is a cyclic dodecapeptide that was originally isolated fr om the fish urophysis, the terminus of a neurosecretory system located in the caudal area of the spinal cord. We have recently isolated and characterized urotensin II in the brain of a tetrapod, the frog Rana r idibunda. Recent reports, suggesting that urotensin II may stimulate c ortisol secretion in fish, prompted us to investigate the possible eff ects of fish and frog urotensin 11 on corticosteroid secretion in amph ibians. Exposure of perifused frog adrenal slices to goby (Gillichthys mirabilis) urophysis extracts induced a marked stimulation of cortico sterone and aldosterone secretion. In contrast, at concentrations rang ing from 10(-10) to 10(-6) M, synthetic goby urotensin 11 had no effec t on corticosteroid production. Similarly, infusion of synthetic frog urotensin II (10(-10) to 10(-6) M) did not modify the spontaneous rele ase of corticosterone and aldosterone. In addition, frog urotensin II had no effect on ACTH- and angiotensin II-induced secretion of cortico steroids. These results show that in frog, urotensin II does not modul ate spontaneous and ACTH-or angiotensin II-evoked adrenal steroidogene sis.