Maturational changes in testicular steroidogenesis: Hormonal regulation of 5α-reductase

Abstract

Studies were undertaken to compare the capacity of the human and rat testis to convert progesterone- 3H ( 3H-P) both to testosterone (T) and 5α-androstane-3α,17β-diol (5α-diol) at various stages of development, and to determine the possible mechanisms regulating the maturational changes in 5a-reductase activity in the rat testis. Testes from 1- and 13-yr-old males converted 3H-P to T (7–13%) and 17-hydroxyprogesterone (3–20%) and several unidentified metabolites. A similar metabolic pattern was obtained when 3H-P was incubated with testicular homogenate of 20-yr-old subjects, with the exception that the formation of T (27%) was higher than in 13-yr-old testis. Very little 5α-reduced androstane products, however, accumulated in these three incubations. Under the same incubation conditions, 90-day-old rat testis converted 3H-P to T, while 28-day-old testis converted 3H-P mainly to 5α-diol (58%). To determine whether 5α-reductase activity is dependent on gonadotropic stimulation, 5α-reductase was measured in seminiferous tubules and interstitial cells following various periods of hypophysectomy. In both testicular compartments, 5α-reductase activity decreased rapidly, reaching a minimal level 7 days following hypophysectomy. Treatment with either FSH or LH (3 days) 2 days following hypophysectomy increased significantly 5α-reductase activity in whole testis. Large doses of testosterone propionate, however, did not appear to increase the activity above the level of the untreated hypophy-sectomized control, indicating that this effect of gonadotropins is not mediated through androgens. These studies clearly demonstrated that neither the immature nor the mature human testis possesses a high level of 5α-reductase activity as compared with the rat testis, and that 5oc-reductase activity in the rat testis is dependent on gonadotropic stimulation, in contrast to the androgen-dependent 5α-reductase in other target tissues.