Bioconversion of Steroids in Immature Rat Testes<i>in Vitro</i>1

Abstract

Among the testicular enzymes related to steroid bioconversion, the Δ5-3β-hydroxysteroid dehydrogenase, together with the isomerase, and the 17β-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 17α-hydroxylase and the pregnene-C17-C20 lyase activities were found to be relatively active in immature rat testes. After incubation of 17 α-hydroxy progesterone and androst-4-ene-3,17-dione separately with the testicular microsomes of immature rats, 3α, 17α- dihydroxy-5α-pregnan-20-one was obtained as one of the major metabolites of 17α-hydroxyprogesterone, and 5α-androstane-3,17-dione, 3β- hydroxy-5α-androstan-17-one, and 3β-hydroxy- 5α-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 Δ4-androstene and -pregnene-5α-reductase, the 5α-androstane-3α-, and -3β-hydroxysteroid dehydrogenases, and the 5α-pregnane-3α-hy droxysteroid 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 two different ages. Administration of human chorionic gonadotrophin to the immature rats caused a remarkable increase of Δ6-3β-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 20α-hydroxysteroid dehydrogenase in immature rat testes, in which spermatogenesis was not observed, was found comparable to the activity of adult rat testes. (Endocrinology79: 579, 1966)