In vitro metabolism of 3H-pregnenolone and 3H-progesterone by adult and prepubertal human testicular tissue before and during gonadotrophic treatment.

The in vitro conversion of tritiated pregnenolone and progesterone was studied in testicular tissue from three infertile adult males before and during 25-30 weeks of therapy with hCG alone or combined with hMG. Furthermore, the in vitro conversion of pregnenolone was studied in testicular tissue from five prepubertal boys with undescended testes, two of whom had been subjected to hCG treatment for 5 weeks. The gonadotrophic treatment appeared to augment the steroid conversion mediated by the enzymes 3 beta-hydroxysteroid dehydrogenase and 17 alpha-hydroxylase in adult as well as prepubertal testicular tissue. The conversion mediated by C17-20-lyase along the delta 4 metabolic pathway was not increased, causing a "trap" along the delta 4 metabolic pathway. The increased production of testosterone in vitro from tritiated pregnenolone, which was observed during gonadotrophic treatment, probably took place along the delta 5 metabolic pathway through the C17-20-lyase step, whereas C21 steroids converted to the delta 4 metabolic pathway were found to be "trapped" as 17 alpha-hydroxyprogesterone.