Nitric oxide (NO) is a free radical that is generated by NO synthase(NOS) from l-arginine. The NO/NOS system is involved in reproductive functions such as steroidogensis, folliculogenesis, ovulation and oocyte meiotic maturation in several species. There is no report about the effect of this system on cumulus expansion of sheep oocyte. Optimal expansion of the cumulus mass appears to be essential for cytoplasmic maturation. The process of cumulus expansion is accompanied by modifications of gap junctions that to occuring it, there is an absolute requirement for a soluble oocyte secreted factor (OSF). In this expriment we cultured sheep cumulus-oocyte complex in different concentrations (0, 1, 10mM) of NOS inhibitor (LNAME), to study the function of NO in expansion of its. L-NAME in the highest concentration (10mM) significantly suppressed full expansion of cumulus cells. Several members of the TGFB superfamily secreted by the oocyte such as GDF-9 and BMP15, mimic the paracrine actions of oocytes in the regulation of cumulus expansion in vitro. So use of L-NAME may be decreases hyaluronan synthesis and other factors that are synthized by cumulus-oocyte complex that plays a role in cumulus expansion. The data from the present research suggest that NO is essential for full expansion of sheep oocyte.

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