BIOSYNTHESIS IN-VIVO AND EXCRETION OF CORTISOL BY FISH LARVAE

There is a posthatching rise in levels of endogenous cortisol during t he ontogeny of those teleosts studied to date. This is thought to be t he result of de novo synthesis of cortisol by the larvae, although the re is no direct evidence for this. The present study aimed to demonstr ate this process in Asian seabass (Lates calcarifer). Larvae (4 days p osthatching) were maintained for up to 12 hours in seawater containing [H-3] 17 alpha-hydroxyprogesterone. High performance liquid chromatog raphy analysis of extracts of the medium, before and after treatment w ith glucuronidase, indicates conversion of the precursor to several me tabolites. One of these was identified as cortisol on the basis of its isopolarity with authentic standard in thin-layer chromatography, and confirmed by recrystallisation to constant specific activity. Immunoh istochemistry on siblings shows that the interrenals are immunoreactiv e for adrenodoxin (adrenal ferredoxin) and cytochrome P-450(21) (stero id 21-monooxygenase [steroid, hydrogen-donor:oxygen oxidoreductase, 21 -hydroxylating]; EC 1.14.99.10), and the pituitary for adrenocorticotr ophic hormone. These findings suggest that the pituitary-interrenal ax is is functional even at this early stage, and are consistent with the hypothesis that the posthatching rise in endogenous cortisol levels i s the result of de novo steroidogenesis. (C) 1997 Wiley-Liss, Inc.