Nitric oxide produced by cumulus cells stimulates maturation of mouse oocytes

The effect of sodium nitroprusside (SNP), a donor of nitric oxide, on meiotic maturation of mouse oocytes was studied by injecting N^w-nitro-L-arginine methyl ester (L-NAME) intra-peritoneal (ip), a nitric oxide synthase inhibitor, or culturing oocytes in the medium supplemented with L-NAME or hypoxanthine (HX) to arrest the spontaneous oocyte maturationin vitro. The results showed that the inhibitory effect of L-NAME by injecting 10 mg/kg ip on extrusion of the first polar body only could be reversed by injecting 2.5 mg/kg SNP with L-NAME simultaneously (P < 0.05). Half an hour later ten mice died when given 10 mg/kg SNP ip. The treatment of some concentrations of SNP (10⁻⁷, 10⁻⁶, 10⁻⁵ mol/L) significantly stimulated meiotic maturation to metaphase II stages in cumulus enclosed oocytes in the presence of HX. However, other concentrations of SNP (10⁻⁸, 10⁻⁴, 10⁻³ mol/L) had no effect on HX-arrested oocyte meiotic maturation. The optimal concentration of SNP on CEOs had no effect on DOs. The dose of 10⁻³ mol/LL-NAME demonstrated a significant suppression in formation of PB₁, but not in GVBD. This inhibition was reversed by the addition of SNP. These results indicated that the physiological levels of NO produced by cumulus cells could stimulate meiotic maturation of mouse oocytes bothin vivo andin vitro.