The inhibition of human testicular testosterone production in vitro by oestrogen was studied by measuring effects of oestradiol-17 beta and ethinyl oestradiol on the 3 beta-hydroxysteroid dehydrogenase/isomerase and the delta 4-pathway of testosterone synthesis. Progesterone, 17 alpha-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, 17 alpha-hydroxyprogesterone or androstenedione was added to the incubation media. The conversion of pregnenolone, progesterone and 17 alpha-hydroxyprogesterone was inhibited by oestrogen. It is concluded that oestrogen inhibits 3 beta-hydroxysteroid dehydrogenase/isomerase, 17 alpha-hydroxylase and C17-20-lyase enzyme activities of human testicular tissue in vitro while 17 beta-ketosteroid reductase activity is unaffected.
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Daehlin et al. (1986) studied this question.
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