[Inhibition of rat liver delta 4-3-ketosteroid-5 alpha-reductase by steroids in vitro].

The inhibition of the hydrogenation of testerone to 5alpha-dihydrotestosterone in microsomes of female rat liver has been studied by progesterone-, testosterone- and estradiol derivatives. In the pregnane series, progesterone, 17alpha-OH-progesterone and its acetate were the strongest inhibitors. In the estradiol series, 3-hydroxy-compounds with a CH2X-substituent at 17alpha-position were stronger inhibitors than the respective 3-methoxy derivatives. The most potent inhibitor till now is an estradiol derivative with a SeCN group in 16alpha-position.