Effects of the new progestagen STS 557 on the biosynthesis of steroids in tissue slices of the human ovary.

To examine the direct effect of STS 557 (17 alpha-cyanomethyl-17 beta-hydroxy-estra-4,9-dien-3-one) on the ovarian biosynthesis of steroids, tissue slices obtained from a cyclically functional human ovary were incubated with [4-14C]-pregnenolone as precursor. The steroid production was determined by measuring the concentration of eleven 14C-labelled steroids in the medium at the end of a 3 h-incubation. The addition of STS 557 to the incubation medium inhibited the biosynthesis of androstenedione, progesterone, 17 alpha-hydroxyprogesterone and oestrone, whereas dehydroepiandrosterone, 17 alpha-hydroxypregnenolone and delta 5-androstenediol increased. The principal manifestation of the effect of STS 557 is the apparent inhibition (87%) of the 3 beta-hydroxysteroid dehydrogenase-delta 5-4-isomerase activity in this experimental model. It is noteworthy, that the effects of STS 557 are similar to those effects previously published for other clinical used progestagens and the "pure antiandrogen" cyproterone. The results indicate, that STS 557 acts directly on the steroid biosynthesis in the human ovary in vitro.