ABSTRACT
OBJECTIVE: Nitric oxide (NO) produced in ovary may contribute to follicle maturation, ovulation, oocyte maturation and luteinization. In this study, the effect of nitric oxide on the spontaneous maturation of mouse oocyte was observed. Method: The index of oocyte maturation was checked by the germinal vesicle breakdown (GVBD) and appearance of polar body (PB) under microscope in the denuded oocytes and oocyte-cumulus complexes (OCCs) from mouse ovarian follicles after 24 hours pregnant-mare serum gonadotropin treatment. RESULTS: The GVBD appeared 50 %, 1 hour and 80 %, 2 hrs after changes of oocytes from dibutyryl cAMP (dbcAMP, 0.5 mM) contained media into dbcAMP-free media. dbcAMP (0.5 mM) completely blocked the GVBD until 24 hrs but dbcGMP (5 mM) delayed the GVBD by 1 hr. Sodium nitroprusside, the NO generator, inhibited the GVBD dose-dependently at 2 hr incubation in denuded and OCCs. The appearance of GVBD was not different between control and dbcGMP or SNP in denuded oocytes and OCCs at 24 hrs incubation. The guanylate cyclase activity in denuded oocyte cytosol was not detected whereas the guanylate cyclase activity in OCCs cytosol was 1.3 nmole/min/mg protein which was increased about 3 times by SNP (100 micrometer). CONCLUSION: These results suggest that the NO in ovary may delay the spontaneous oocyte maturation in early stage by acting on the maturation signaling protein as well as guanylate cyclase.