Mevinolin (lovastatin) inhibits androstenedione production by porcine ovarian theca cells at the level of the 17α-hydroxylase: C-17, 20-lyase complex

Abstract

Mevinolin, putatively a specific inhibitor of 3- hydroxy-3-methylglutaryl coenzyme-A reductase, was used to assess the contribution ofde novo synthesized cholesterol to androgen production by ovarian thecal cellsin vitro. Enzymatically dispersed thecal cells from 3- to 6-mm follicles of prepubertal gilts were incubated at 150, 000 cells/ml with a maximally effective dose of LH (250 ng/ml) for 24 h. Mevinolin (3-50 μM) caused dose-dependent inhibition of androstenedione production. Addition of 25-hydroxycholesterol (0.025-25 μM) failed to restore androstenedione production to levels seen in the absence of mevinolin, suggesting an additional site of action of mevinolin beyond 3-hydroxy-3-methylglutaryl coenzyme reductase. the site of this inhibitory effect was determined by measuring steroid products formed in the presence of relevant steroid precursors. Mevinolin (12 μM) inhibited the production of 17α-hydroxyprogesterone from progesterone and that of androstenedione from 17α-hydroxyprogesterone, while 25-hydroxycholesterol to progesterone and pregnenolone to progesterone conversions were unimpaired. That mevinolin did not affect 3 β-hydroxysteroid dehydrogenase: 54-isomerase reactions was confirmed by demonstrating that conversions of pregnenolone, 17α-hydroxypregnenolone, and dehydroepiandrosterone to progesterone, 17α-hydroxyprogesterone, and androstenedione, respectively, were not affected by 12 μM mevinolin. These results indicate that mevinolin has an additional inhibitory action at the level of the 17α-hydroxylase:C-17, 20-lyase complex. the degree of inhibition of androstenedione production was not decreased with increased concentrations of progesterone or 17α-hydroxyprogesterone substrate, suggesting that the inhibition was not competitive in nature. As the dose of mevinolin was increased up to 50 μM, progesterone accumulation was unaffected, but pregnenolone concentrations in medium greatly increased. While the mechanism of this effect is unclear, this finding suggests that preformed intracellular cholesterol, rather than that synthesizedde novo, is supplying steroidogenic substrate in these cells. © 1989 by The Endocrine Society.