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Abstract
The inhibition of human testicular testosterone production in vitro by oestrogen was studied by measuring effects of oestradiol-17β and ethinyl oestradiol on the 3β-hydroxysteroid dehydrogenase/isomerase and the Δ4-path-way of testosterone synthesis. Progesterone, 17α-hydroxyprogesterone, androstenedione and testosterone concentrations of incubation media were all depressed after oestrogen addition. To minimize differences in substrate amounts between incubations, 3H-labelled pregnenolone, progesterone, 17α-hydroxyprogesterone or androstenedione was added to the incubation media. The conversion of pregnenolone, progesterone and 17α-hydroxyprogesterone was inhibited by oestrogen. It is concluded that oestrogen inhibits 3β-hydroxysteroid dehydrogenase/isomerase, 17α-hydroxylase and C17-20-lyase enzyme activities of human testicular tissue in vitro while 17β-ketosteroid reductase activity is unaffected.