The Functional Role of Oxytocin in the Induction of Oocyte Meiotic Resumption in Cattle

Contents The aim of the present study was to examine the role of oxytocin ( OT ) in the progesterone ( P 4) and prostaglandins ( PG s) pathway to induce oocyte meiotic resumption. Cumulus–oocyte complexes were co‐cultured with follicular hemisections for 15 h to determine the effects of different doses of OT or atosiban ( ATO ; oxytocin receptor antagonist) on oocyte meiotic resumption. In another experiment, we examined the effect of the interaction between P 4, OT and PG s on the regulatory cascade of the oocyte meiotic resumption. Oxytocin at 1 μ m was effective in inducing meiotic resumption in oocytes co‐cultured with follicular cells (84.0%), not differing from the positive control group (74.4%). Atosiban inhibited in a dose‐dependent manner the positive effect of OT on the meiotic resumption (27.6% metaphase I with 10 μ m of ATO , which did not differ from the 25.5% of the negative control group). Furthermore, a third experiment showed that P 4 was able to induce oocyte meiotic resumption, which was inhibited by ATO . However, the OT positive effect was not blocked by mifepristone ( P 4 antagonist), but was inhibited by indomethacin (a non‐selective PTGS 2 inhibitor). Collectively, these data suggest a sequential role of P4, OT and PG s in the induction of oocyte meiotic resumption.