Abstract
The germinal vesicle (GV) of follicle-enclosed oocytes in mice remains arrested at the dictyate state of meiosis. Upon releasing the oocytes from the follicles, the meiotic process resumes, leading to dissolution of the GV, suggesting that factors in the follicular constituents sustain the meiotic arrest of oocytes. Vasoactive intestinal peptide (VIP) was demonstrated in the ovary and found to have a wide range of biological effects. In this study, the possibility of VIP to be a factor which induces meiosis-arrest of oocytes was evaluated. Porcine VIP inhibited resumption of meiosis of cumulus-enclosed mouse oocytes in vitro. Germinal vesicle breakdown (GVBD) was prevented in more than 50% of the oocytes treated by VIP at a concentration of 30 microM. The inhibiting effect of VIP was dose-dependent and reversible. Spontaneous resumption of meiosis of isolated oocytes in vitro was reported to be inhibited by dibutyryl cAMP (dbcAMP) added to the medium, indicating that meiotic arrest can be sustained by maintaining intra-oocyte cAMP above a critical level. It was further reported that follicular fluid contains substances that maintain meiotic arrest in association with exogenous dbcAMP. In the present study, the blocking activity of dbcAMP for the spontaneous resumption of meiosis was not potentiated by the addition of VIP in the medium. The present results suggest that VIP may play a role in the regulation of resumption of oocyte meiosis, and that VIP is not a substance which maintains meiotic arrest in association with cAMP.
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