Ginsenosides promote meiotic maturation of mouse oocytes in cumulus-oocyte complexes involving increased expression of nitric oxide synthase

Ginseng has long been used in Asia because of its beneficial effects on human health. Ginsenosides are the primary biologically active components in ginseng. The aim of the present study was to determine the role of ginsenosides on meiotic maturation of murine oocytes to better understand the effects of ginsenosides on reproductive health. Cumulus-oocyte complexes (COCs) and denuded oocytes in germinal vesicle stage were isolated from equine chorionic gonadotropin-primed immature mice and were cultured for 24 hours in 10% fetal calf serum medium, which was supplemented with 4 mmol hypoxanthine to maintain meiotic arrest. Ginsenosides (1.0-10 μg/mL) overcame the hypoxanthine-maintained meiotic arrest. In addition, ginsenosides-stimulated meiotic maturation in COCs was assessed by increased germinal vesicle breakdown and first polar body extrusion. No effect of ginsenosides was observed on denuded oocytes. In addition, ginsenosides (1.0 μg/mL) could synergize with follicle-stimulating hormone (0.1 IU/mL) to promote oocyte meiotic maturation in COCs. Tamoxifen (an estrogen receptor α antagonist) did not influence the ginsenosides-induced meiotic maturation, suggesting the effect was not mediated by estrogenic action. However, a nitric oxide (NO) synthase inhibitor, Nω-nitro-l-arginine methyl ester (l-NAME, 1 mmol), reduced the ginsenosides-induced oocyte maturation in COCs. Immunocytochemical analysis demonstrated that ginsenosides enhanced expression of inducible nitric oxide synthase (iNOS) in the cumulus cells. l-NAME reduced the ginsenoside-induced increase in iNOS immunoreaction. Our results indicate that ginsenosides might stimulate meiotic maturation of mouse oocytes through a paracrine pathway involving the NO/iNOS system.