ABSTRACT
<p><b>AIM</b>To study whether melatonin has effect on oocyte maturation of mouse in vitro.</p><p><b>METHODS</b>Mouse oocytes were cultured in maturation medium, HX-medium, or HX-medium supplemented with FSH, and the effects of MT on meiotic maturation of mouse oocyte were examined.</p><p><b>RESULTS</b>(1) MT at all doses of 0.1 g/L, 0.02 g/L, 0.4 g/L or 0.8 g/L inhibited the formation of PB1 in CEO cultured in maturation medium and had no effect on GVBD. (2) MT could delay GVBD and the extrusion of PB1 in CEOs of mouse oocytes by dynamic curves. In contrast to the control, GVBD and PB1 extrusion of oocytes in the treated groups had been delayed by 8-10 hours and 3-4 hours respectively. (3) MT inhibited the effect of FSH on resumption of meiosis, but no effect on the formation of PB1. (4) MT and HX had cooperation effects on spontaneous oocyte maturation in CEO, but not in DO.</p><p><b>CONCLUSION</b>MT is able to affect mouse oocyte maturation and the regulation mechanisms may be related to cumulus cells.</p>