Luteinization factor-stimulated steroidogenesis in porcine granulosa cells

Luteinization stimulator (LS), an intrafollicular compound of preovulatory (5-8 mm) follicles, increased both the basal and gonadotropins-stimulated p roduction of progesterone by immature (1-3 mm) granulosa cells. The mechani sm by which LS enhance steroidogenesis was investigated by studying the mod ulation of progesterone biosynthesis from exogenous cholesterol and pregnen olone in cultured porcine granulosa cells in serum-free medium. Progesteron e production by cultured granulosa cells was stimulated by FSH, while treat ment with 22-OH-cholesterol further enhanced the gonadotropin action. The a ctivity of LS was found in cell conditioned media obtained after May cultiv ation of preovulatory granulosa cells. Conversion of 22-OH-cholesterol into progesterone by granulosa cells isolated from small follicles was signific antly stimulated in the presence LS in culture media. Also, progesterone pr oduction by granulosa cells in the presence of pregnenolone was increased c onsiderably. Concomitant treatment with LS led to a further augmentation in progesterone synthesis. Endogenous formation of pregnenolone was inhibited by aminoglutethimide. Thus, LS enhancement of progesterone production in c ultured porcine granulosa cells is associated with an increase in the activ ity of cytochrome P450 cholesterol side-chain cleavage and 3 beta hydroxyst eroid dehydrogenase enzymes.