THE IN-VITRO METABOLISM OF 17-HYDROXYPROGESTERONE BY OVARIES OF THE GOLDFISH, CARASSIUS-AURATUS, IS AFFECTED BY SUBSTRATE CONCENTRATION

Ovaries of mature goldfish (Carassius auratus) were incubated with 17- [H-3]hydroxyprogesterone and 0, 0.01, 0.1, 1, 10, and 100 mu g/ml 17-h ydroxyprogesterone (17P). The major products were quantified after sep aration by thin-layer and high-performance chromatography. The results show that substrate concentration markedly affects the pattern of met abolites. Glucuronides and sulfates decreased from 7.2 +/- 2.0 and 28. 5 +/- 4.4% of recovered radioactivity, respectively, in the absence of added 17P to insignificant yields at 10 mu g/ml 17P. 7 alpha-Tetrols were the major products (36-52%) with 0-1 mu g/ml substrate, but at 10 and 100 mu g/ml 17,20 alpha-dihydroxy-4-pregnen-3-one (17,20 alpha P) was the major metabolite and there were low yields of other products. 11-Deoxycortisol was produced in significant amounts only at low subs trate concentrations. The results support the hypothesis that 5 alpha- reduced-7 alpha-hydroxylated metabolites are formed by enzymes of high activity but low capacity and serve to limit secretion of 17,20 alpha P and its 20 beta epimer to the period of maximum GtH stimulation. (C ) 1994 Academic Press, Inc.