title: Influence of 20 alpha-dihydroprogesterone on progesterone output by human chorion explants.
abstract: The output of progesterone by explants of chorion incubated without exogenous precursor was increased in the presence of 20 alpha-dihydroprogesterone (20 alpha-diHP). We have now examined the nature of the 20 alpha-diHP effect. Explants of chorion were incubated with [3H]progesterone and 3 microM non-radiolabelled 20 alpha-diHP to examine the effect of 20 alpha-diHP on progesterone metabolism. Significantly more radioactivity remained as unmetabolized [3H]progesterone compared to chorion incubated in the absence of non-radiolabelled 20 alpha-diHP. There was also a decrease in the output of [3H]-20 alpha-diHP by the explants but no change in the output of a second metabolite of progesterone [3H]-5 alpha-pregnanedione. When explants were incubated with 20 alpha-diHP in the presence of the 3 beta-hydroxysteroid dehydrogenase inhibitor, trilostane, the output of progesterone was significantly greater than with explants incubated with trilostane but without addition of 20 alpha-diHP. Radiochemically pure [3H]progesterone was produced by explants of chorion incubated with [3H]-20 alpha-diHP. We conclude that 20 alpha-diHP may serve as substrate for chorionic progesterone production through 20 alpha-hydroxysteroid dehydrogenase. 20 alpha-diHP, formed from progesterone, may also exert product feedback inhibition on this enzyme.
authors.forename: W A
authors.initials: WA
authors.lastname: Powell
authors.forename: J R
authors.initials: JR
authors.lastname: Challis
mesh_terms: D004092:20-alpha-Dihydroprogesterone / Q000378:metabolism / Q000494:pharmacology*; D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors; D002823:Chorion / Q000378:metabolism*; D046508:Culture Techniques; D013196:Dihydrotestosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D006801:Humans; D011374:Progesterone / Q000031:analogs & derivatives* / Q000378:metabolism*
chemical_list: D013196:Dihydrotestosterone; D004092:20-alpha-Dihydroprogesterone; D011374:Progesterone; D015096:3-Hydroxysteroid Dehydrogenases; C009954:trilostane