title: Pregnenolone biosynthesis by cultured rat granulosa cells: modulation by follicle-stimulating hormone and gonadotropin-releasing hormone.
abstract: The mechanism by which GnRH inhibits ovarian progesterone production was investigated by studying the GnRH modulation of pregnenolone biosynthesis in cultured rat granulosa cells. Granulosa cells from hypophysectomized, estrogen-treated rats were incubated for 2 days with various hormones in vitro. Pregnenolone production was measured in the presence of cyanoketone, which inhibits the conversion of pregnenolone to progesterone. FSH stimulated pregnenolone production in a dose-dependent manner (ED50, 4.47 ng/ml). Concomitant treatment with GnRH resulted in a dose-dependent decrease in FSH-stimulated pregnenolone production (ID50, 6.3 x 10(-9) M; maximal decrease, approximately 50%). In contrast, treatment with high doses of GnRH alone stimulated pregnenolone production (ED50, 2.95 x 10(-8) M) reaching a maximal level of about 10% that induced by FSH. Treatment with a GnRH antagonist, [Ac-D-Phe1, D-pCl-Phe2, D-Trp3,6]GnRH, did not affect either basal or FSH-stimulated pregnenolone production, but blocked both inhibitory and stimulatory effects of GnRH. The addition of 25-hydroxycholesterol, a soluble substrate for side-chain cleavage enzymes, enhanced FSH-stimulated pregnenolone production, but failed to overcome the inhibitory action of GnRH. GnRH also inhibited progesterone production stimulated by 8-bromo-cAMP and cholera toxin. This action of GnRH, however, was not associated with an inhibition of pregnenolone biosynthesis, but appeared to be due to a preferential increase in the metabolism of progesterone to 20 alpha-hydroxypregn-4-en-3-one. Thus, in addition to the reported GnRH stimulation of progesterone metabolism to 20 alpha-hydroxypregn-4-en-3-one and the GnRH inhibition of FSH-stimulated 3 beta-hydroxysteroid dehydrogenase activity, the present results demonstrate that GnRH also inhibits FSH-stimulated pregnenolone biosynthesis, probably at the side-chain cleavage enzyme step.
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000735:Androstenedione / Q000494:pharmacology; D000818:Animals; D003489:Cyanoketone / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006107:Granulosa Cells / Q000378:metabolism*; D006888:Hydroxycholesterols / Q000494:pharmacology; D011284:Pregnenolone / Q000096:biosynthesis*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D006888:Hydroxycholesterols; D015124:8-Bromo Cyclic Adenosine Monophosphate; D007987:Gonadotropin-Releasing Hormone; D000735:Androstenedione; D003489:Cyanoketone; D011284:Pregnenolone; C007997:25-hydroxycholesterol; D005640:Follicle Stimulating Hormone; D000242:Cyclic AMP; D015096:3-Hydroxysteroid Dehydrogenases