In vitro metabolism of progesterone and 17 alpha-hydroxyprogesterone in the testis of the rainbow trout, Salmo gairdneri Rich., at different stages of spermatogenesis.

Rainbow trout testicular fragments were incubated at 8 different stages of the spermatogenetic cycle in the presence of tritiated progesterone or 17 alpha-hydroxyprogesterone. This paper describes the potential enzymatic activities involved in the delta 4 route leading to the production of "major" derivatives. 1) A 5-reductase converted progesterone into 5 alpha (beta)-pregnane-3,20-dione. 2) A 20 beta-oxydoreductase converted 17 alpha-hydroxyprogesterone into 17 alpha-hydroxy-20 beta-dihydroprogesterone. At some stages this synthesis reached or exceeded androgen production. 3) 20 beta-oxydoreductase, 17-20 desmolase and 17 beta-oxydoreductase are proposed as putative enzymatic steps in the regulation and modulation of steroidogenic metabolism in the trout testis. 4) The physiological role of the different major steroids synthesized by the testis in vitro is discussed, and the hypothesis of the involvement of 17 alpha-hydroxy-20 beta-dihydroprogesterone in the control of germ cell mitotic activity and/or feedback on the hypothalamo-pituitary system is examined.