The biosynthesis of 11-ketotestosterone by the testis of the Siamese fighting fish Betta splendens Regan (Anabantoidei, Belontiidae).

Testicular tissues of the Siamese fighting fish were incubated with [14C]pregnenolone for 10, 20, 30, 50, 80, and 120 min, and with [14C]progesterone, [14C]11 beta-hydroxyandrostenedione, [14C]11 beta-hydroxytestosterone, and [14C]androstenetrione for 120 min. 11-Ketotestosterone was the main metabolite in all 120-min incubations. No 11-oxygenated C21 steroids were found as metabolites of either pregnenolone or progesterone. The biosynthesis of 11-ketotestosterone proceeded through both the delta 5- and the delta 4- pathways as judged from the shape of the yield-time curves of the metabolites of pregnenolone. 11-Ketotestosterone formation from 11-oxygenated precursors increased in the order 11 beta-hydroxytestosterone less than 11 beta-hydroxyandrostenedione less than androstenetrione.