In vitro conversion of 3H-pregnenolone by human testicular tissue from fetal age to senescence.

The in vitro conversion of pregnenolone was studied in testicular tissue specimens from 6 fetuses, 3 prepubertal boys with undescended testes, 5 normal adult men, and 12 elderly males with prostatic carcinoma. Adult testicular tissue converted pregnenolone to testosterone mainly along the delta 5 metabolic pathway. Steroid intermediates that were converted from pregnenolone to delta 4 metabolites prior to the rate limiting C17-20 lyase step were "trapped" as 17 alpha-hydroxyprogesterone. The conversion patterns in testicular tissue from fetuses were similar to those in testicular tissue from adults and elderly men. In prepubertal testicular tissue, however, a significantly lower conversion was observed, mediated by the enzymes 3 beta-hydroxysteroid dehydrogenase/isomerase and 17 alpha-hydroxylase. The conversion mediated by 17 alpha-hydroxylase was significantly lower in testicular tissue from the elderly males than from younger adults, suggesting a relative steroidogenic insufficiency in the elderly males. Testicular tissue from an anencephalic fetus produced testosterone and steroid intermediates in vitro, although to a lesser extent than in testicular tissue from other fetuses. The enzymes 3 beta-hydroxysteroid dehydrogenase/isomerase and 17 alpha-hydroxylase appeared to be under gonadotropic control.