Gonadotropins I and II do not stimulate the in vitro secretion of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one 20-sulphate by rainbow trout gonads during final sexual maturation

The in vitro secretion of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one 20-sulphate (17 alpha,20 beta-P-sulphate) and the free steroid 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta-P), by rainbow trout (Oncorhynchus mykiss) gonads, in response to gonadotropin (GTH) I and GTH II, were studied during the final stages of sexual maturation. Substantial amounts of 17 alpha,20 beta-P-sulphate were produced, by both mature ovaries and testes, indicating considerable 20 beta-hydroxysteroid sulphotransferase (20 beta-HST) activity within these tissues. In the post-ovulatory ovary the level of 17 alpha,20 beta-P-sulphate (36.6 ng ml(-1)) greatly exceeded that of 17 alpha,20 beta-P (8.59 ng ml(-1)). The amount of 17 alpha,20 beta-P-sulphate produced in incubations of both mature ovary and testes was unaffected by either GTH I or GTH II treatment at physiological concentrations up to 100 ng ml(-1) Similarly, incubations of maturing ovary and testes, treated with GTH I or GTH II, in the presence of added 17 alpha,20 beta-P at 100 ng ml(-1) of medium, produced levels of 17 alpha,20 beta-P-sulphate that were similar to those of the controls. In incubations of mature ovarian follicles at the stages of germinal vesicle breakdown and preovulation, both GTHs significantly stimulated secretion of 17 alpha,20 beta-P, although GTH II was always more potent than GTH I. GTH II significantly elevated the levels of 17 alpha,20 beta-P in testicular incubations from mature males more than 4-fold relative to GTH I and controls, which did not differ from one another. In conclusion, 20 beta-HST, the enzyme responsible for the sulphate conjugation of 17 alpha,20 beta-P, was found to be active in the ovaries and testes of rainbow trout in vitro. However, the levels of this enzyme do not appear to be regulated by either GTH I or GTH II.