Cellular localization of 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase in the seminiferous tubule of the rat testis.

Seminiferous tubules isolated from normal adult rats converted (14C) testosterone to (14C) androstanediol and (14C) androstenedione as the major metabolites; (14C) dihydrotestosterone and (14C) androsterone were produced in lesser amounts. Tubules from immature rats (26-28 days of age) converted a higher proportion of (14C) testosterone to 5alpha-reduced products than did tubules from adult rats. Spermatocyte-enriched preparations contain 5alpha-reductase. The lower level of 5alpha-reductase activity in spermatid-spermatocyte preparations indicates that this enzyme is low or absent in spermatids. Sertoli cell-enriched preparations contain 5 alpha-reductase and a high level of 3alpha-hydroxysteroid dehydrogenase. The results show that spermatocytes and Sertoli cells have the capacity to metabolise (14C) testosterone to 5alpha-reduced products; dihydrotesterone is the major product formed by spermatocytes, whereas in Sertoli cells further metabolism to 5alpha-androstane-3alpha, 17beta-diol occurs.