Gonadal Steroidogenesis and Gametogenesis in Teleost Fishes — A Study on the Sea Bass,Dicentrarchus LabraxL.

Steroid hormone biosynthesis by the gonads of the teleost Dicentrarchus labrax was studied in vitro. The testicular tissue at maturity metabolized [4-14C] pregnenolone into the following steroids identified through their isopolarity and isomorphism with authentic compounds: progesterone, 11-ketoprogesterone, 17α-hydroxyprogesterone, 21-deoxycortisol, androstenedione, 11β-hydroxyandrostenedione, testosterone, 11β-hydroxytestosterone and 11-ketotestosterone. The lack of 5-ene-3β-hydroxy intermediates and the large excess of 21-deoxycortisol over 11-deoxyandrogens suggest that 11-oxygenated androgens were formed mainly through the following route: pregnenolone → progesterone → 17α-hydroxyprogesterone → 21-deoxycortisol → 11β-hydroxyandrostenedione. The conversion of the latter into the other 11-oxygenated androgens was accomplished maintaining a balance strongly in favor of 11β-hydroxyandrostenedione and 11-ketotestosterone. As to the ovary, steroidogenesis associated with the condition of widespread follicular atresia, as found in females confined to low salinity biotopes, was investigated. Incubations with [4-14C] pregnenolone and [4-14C] progesterone yielded a small amount of progesterone from pregnenolone and no steroid hormone from progesterone, despite an active metabolism of both precursors. It seems that the phagocytic conversion of the follicular cells during atresia is incompatible with the maintenance of their endocrine function.