Publication Abstract

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

Gonadotropins I and II do notstimulate the in vitro secretion of 17beta,20ß-dihydroxy-4-pregnen-3-one 20-sulphate byrainbow trout gonads during final sexual maturation

J.J. Nagler, A.P. Scott, C.R. Tyler and J.P. Sumpter

The in vitro secretion of 17α,.20β-dihydroxy-4-pregnen-3-one 20-sulphate (17α,20β-P-sulphate) and the free steroid 17α,20β-dihydroxy-4-pregnen -3-one (17α,20β-P), by rainbow trout (Oncorhynchus mykiss) gonads, in response toaonadotropin (GTH) I and GTH II, were studied during the final stages of sexualmaturation. Substantial amounts of 17α,20β-P-sulphate were produced, by both mature ovaries and testes, indicatingconsiderable 20P-hydroxysterold sulphotransferase (20β-HST) activity within these tissues. In the post-ovulatory ovary thelevel of 17α,20β-P-sulphate (36.6 ng ml^-1)greatly exceeded that of 17α,20β-P(8.59 ng ml^-1). The amount of 17α,20β-P-sulphate produced in incubations of both mature ovary and testes wasunaffected by either GTH I or GTH II treatment at physiological concentrations up to 100ng ml^-1. Similarly, incubations of maturing ovary and testes, treated with GTHI or GTH II, in the presence of added 17α,20β-P at 100 ng ml^-1 of medium, produced levels of 17α,20β-P-sulphate that were similar to thoseof the controls. In incubations of mature ovarian follicles at the stages of germinalvesicle breakdown and preovulation, both GTHs significantly stimulated secretion of 17x,20β-P, although GTH II was alwaysmore potent than GTH I. GTH II significantly elevated the levels of 17α,20β-P in testicular incubations from maturemales more than 4-fold relative to GTH I and controls, which did not differ from oneanother.

In conclusion, 20β-HST, the enzyme responsible for thesulphate conjugation of 17α,20β-P,was found to be active in the ovaries and testes of rainbow trout in vitro. However, thelevels of this enzyme do not appear to be regulated by either GTH I or GTH II.

Reference:

J.J. Nagler, A.P. Scott, C.R. Tyler and J.P. Sumpter, 1996. Gonadotropins I and II do notstimulate the in vitro secretion of 17beta,20ß-dihydroxy-4-pregnen-3-one 20-sulphate byrainbow trout gonads during final sexual maturation. Fish Physiology and Biochemistry, 15:149-156.

J.J. Nagler, A.P. Scott*, C.R. Tyler and J.P. Sumpter

Fish Physiology and Biochemistry, 15: 149-156