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Interleukin-6 (IL-6) and its receptor components have been shown to be present in rat follicular granulosa cells. The present study was designed to examine the effect of this cytokine on changes in expression of the luteinizing hormone receptor (LHR) messenger RNA and of the steroidogenic enzyme, CYP11A1 (cytochrome P450 scc) in an in vitro model of granulosa cell maturation. Ovarian granulosa cells harvested from immature rats 2 days after treatment with equine chorionic gonadotropin were cultured for 48 h in media containing 10% fetal bovine serum. They were then transferred to a chemically defined serum-free medium and cultured for an additional 72 h. Within 24 h of transfer, the expressions of LHR and CYP11A1 mRNA increased significantly and remained increased for 72 h. The cells responded to exposure to FSH, but not LH, by an increase in production of cAMP before the additional 72 h of culture. The cAMP response to LH was attained within 24 h and persisted for 72 h, whereas the response to FSH decreased continuously with time. Inclusion of IL-6 in the culture medium caused a dose-dependent decrease in expression of LHR mRNA, in addition to a decrease in the cAMP response to LH. Immunoneutralization of endogenous granulosa cell IL-6 resulted in an increase in expression of LHR mRNA, but not CYP11A1 mRNA. The results are consistent with the view that IL-6 may have a physiological role in the maturation of ovarian follicles by modulating the attainment of the LHR in granulosa cells.

Vascular endothelial growth factor (VEGF) is known to be necessary for the vascularization of the developing corpus luteum. Our recent data suggested that cyclooxygenase-II (COX-II) may play a role in the formation of vascular plexuses in developing corpora lutea of the rat. Here we examined the relationship between VEGF and the expression of prostaglandin (PG)- metabolizing enzymes in rat ovarian luteal cells. VEGF treatment caused a dose-dependent increase in the expression of COX-II and membrane-associated PGE synthase (mPGES) mRNA in cultured rat luteal cells. However, pretreatment of the luteal cells with a selective COX-II inhibitor, NS-398, abolished the VEGF-enhanced mPGES mRNA expression. VEGF also increased PGE₂ secretion. Conversely, PGE₂ dose-dependently stimulated VEGF mRNA expression. Furthermore, VEGF induced VEGF mRNA expression, but this effect was abolished by NS-398 pretreatment. These findings suggest that VEGF enhances PGE₂ production by stimulating COX-II and mPGES expression in rat corpus luteum and that the effect of VEGF on luteal cells may be partially mediated by this stimulation of PGE₂ production.