Extragonadal production of 17,20-dihydroxy-4-pregnen-3-ones in vitro in cyprinid fish.

Muscle, heart, eye, testis, blood, and sperm of trout and goldfish have been examined for the presence of 20-hydroxysteroid dehydrogenase by incubation with [3H]17-hydroxyprogesterone in the presence of 0, 0.1, 1, or 10 micrograms/ml of unlabeled substrate. In trout, 17-hydroxyprogesterone was metabolized only by sperm and testis, with 17,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P) as the major product and traces (< 2%) of 17,20 alpha-dihydroxy-4-pregnen-3-one (17,20 alpha P). In goldfish, maximum conversion of 17-hydroxyprogesterone to 17,20 alpha P was over 30% per 100 mg tissue in eyeball, heart, and testis, 12% per 20 microliters blood, and 18% per 20 microliters sperm, but less than 5% per 100 mg muscle. 17,20 alpha P was the only metabolite of 17-hydroxyprogesterone in all incubations of nongonadal tissue in goldfish. Within the cyprinid eye, there was no significant activity in the lens, the fluids, or the retina. The possible relationship between the teleost 20 alpha- and 20 beta-hydroxysteroid dehydrogenases, the mammalian 20-hydroxysteroid dehydrogenases, and members of the aldo-keto reductase and short-chain dehydrogenase superfamilies is discussed.