Effects of nitric oxide synthase inhibition on goat oocyte meiotic maturation

Abstract. Nitric oxide is a biological signalling molecule that plays a crucial role in oocyte maturation of mammalians. It is generated by the nitric oxide synthase enzyme from L-arginine. In this study we assessed the effect of nitric oxide synthase inhibition by Nω-nitro-L-arginine methyl ester (L-NAME) on meiotic maturation of goat oocytes. So, different concentrations of L-NAME (0.1, 1, 10 mM) were added to the maturation medium to evaluate the effect of inhibiting nitric oxide synthase on cumulus expansion and meiotic resumption of goat oocytes. The results showed that none of the concentrations affected cumulus expansion but the formation of the first polar body of the oocytes was suppressed in a dose dependent manner. The highest inhibitory effect was observed with 10 mM L-NAME. Moreover, to confirm the results and to evaluate whether this effect is reversible, 0.1 mM sodium nitroprusside (a nitric oxide donor) was added only to the maturation medium which had the highest concentration of L-NAME (10 mM). The concomitant addition of nitric oxide synthase inhibitor with nitric oxide donor reversed the inhibitory effect of L-NAME on meiotic maturation. These results indicated that the nitric oxide / nitric oxide synthase system is involved in the maturation of goat oocytes and that nitric oxide requirement for nuclear maturation is higher than that for cumulus expansion.