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 production of progesterone by immature (1-3 mm) granulosa cells. The mechanism by which LS enhance steroidogenesis was investigated by studying the modulation of progesterone biosynthesis from exogenous cholesterol and pregnenolone in cultured porcine granulosa cells in serum-free medium. Progesterone production by cultured granulosa cells was stimulated by FSH, while treatment with 22-OH-cholesterol further enhanced the gonadotropin action. The activity of LS was found in cell conditioned media obtained after 3-day cultivation of preovulatory granulosa cells. Conversion of 22-OH-cholesterol into progesterone by granulosa cells isolated from small follicles was significantly stimulated in the presence LS in culture media. Also, progesterone production by granulosa cells in the presence of pregnenolone was increased considerably. 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 cultured porcine granulosa cells is associated with an increase in the activity of cytochrome P450 cholesterol side-chain cleavage and 3beta hydroxysteroid dehydrogenase enzymes.