Bioconversion of Steroids in Immature Rat Testesin Vitro1

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Abstract
Among the testicular enzymes related to steroid bioconversion, the [DELTA]5-3[beta]-hydroxysteroid dehydrogenase, together with the isomerase, and the 17[beta]-hydroxysteroid dehydrogenase activities per testis were found to be low in the testicular microsomes of immature rats (27-day-old), in comparison with those of adult rats (90-day-old), while the 17[alpha]~hydroxylase and the pregnene-C17-C20 lyase activities were found to be relatively active in immature rat testes. After incubation of 17[alpha]-hydroxyprogesterone and androst-4-ene-3,17-dione separately with the testicular microsomes of immature rats, 3[alpha], 17[alpha]-dihydroxy-5[alpha]-pregnan-20-one was obtained as one of the major metabolites of 17[alpha]-hydroxy-progesterone, and 5[alpha]-androstane-3, 17-dione, 3[alpha]-hydroxy-5[alpha]-androstan-17-one, and 3[beta]-hydroxy-5[alpha]-androstan-17-one as metabolites of both substrates. The enzymic pattern unique to the testes of immature rats would seem to be the significantly strong activities of the [DELTA]4 -androstene and -pregnene-5[alpha]-reductase, the 5[alpha]-androstane-3[alpha]-, and -3[beta]-hydroxy-steroid dehydrogenases, and the 5[alpha]-pregnane-3[alpha]-hydroxysteroid dehydrogenase; however, the quantity of testosterone produced by immature rat testes was detectable when sufficient substrate was supplied. The in vitro biosynthesis of luteinizing hormone by the anterior pituitary gland was found to be far less in the immature rats than in the adult rat, though the activities per unit weight of anterior lobe were almost comparable between the rats at the 2 different ages. Administration of human chorionic gonadotropin to the immature rats caused a remarkable increase of [DELTA]5-3[beta]-hydroxysteroid dehydrogenase activity specifically among the enzymes examined, and also an increase in the weights of accessory organs, arising from an enhanced production of androgen. The specific activity of the 20[alpha]-hydroxysteroid dehydro-genase in immature rat testes, in which spermatogenesis was not observed, was found comparable to the activity of adult rat testes.