Ryoichi Arai

Steroid biosynthesis in vitro by testes of rainbow trout, Salmo gairdneri ☆

After incubation of progesterone-4-14C with the testicular homogenate of rainbow trout (Salmo gairdneri), radioactive 17α-hydroxyprogesterone, 17α,20β-dihydroxypregn-4-en-3-one, androst-4-ene-3,17-dione and testosterone were obtained as metabolites of progesterone. Testosterone, 11β-hydroxytestosterone and 11-ketotestosterone were confirmed as metabolites of androst-4-ene-3,17-dione-4-14C by the fish testicular homogenate, but neither 11β-hydroxyandrost-4-ene-3,17-dione nor adrenosterone was detected as its metabolite. The incubation products were respectively identified by their mobilities on thin layer chromatograms, chemical characteristics in comparison with the corresponding authentic preparations, and finally on the basis of constant specific activities throughout repeated crystallizations with respective reference preparations. These studies demonstrated the presence of 17α-hydroxylase, 20β-hydroxysteroid dehydrogenase, 17α-hydroxyprogesterone C17-C20 lyase, 17β-hydroxysteroid dehydrogenase, 11β-hydroxylase and 11β-hydroxysteroid dehydrogenase in rainbow trout testes. The biosynthetic studies suggest a pathway of testosterone formation from progesterone in the testicular tissue of this fish similar to that which is reported for mammalian testes. However, rainbow trout testes furthermore forms 11-ketotestosterone from androst-4-ene-3,17-dione probably through testosterone and 11β-hydroxytestosterone, which sequence of bioconversion was not observed for normal mammalian testes.