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There is abundant evidence that cAMP plays an important role in maintaining meiotic arrest in mammalian oocytes. In mouse oocytes, cAMP and cAMP-dependent protein kinase (PKA) form part of a negative pathway which participates in the maintenance of meiotic arrest. In the present experiment, involvement of PKA on the meiotic arrest of pig oocytes was examined using PKA specific inhibitor H89. Cumulus-enclosed oocytes with or without parietal granulosa tissue were incubated in H89-supplemented medium for various durations, and subsequently cultured in H89-free medium for a total of 24 hr. Over 95% of both types of oocytes were arrested at the germinal vesicle stage after 24 hr in H89-free medium. On the other hand, after H89 treatment, about 40% (75 μM H89 for 6 hr, and 100 μM for 4 hr) of cumulus-enclosed oocytes with parietal granulosa tissue and about 70% (50 μM for 6 hr, and 75 μM for 4 hr) of cumulus-enclosed oocytes without granulosa tissue underwent germinal vesicle breakdown (GVBD), respectively. Pig denuded oocytes released from granulosa cells resumed meiosis spontaneously (75% GVBD), but the spontaneous resumption was inhibited by a component of pig follicular fluid, hypoxanthine (12% GVBD). Under the inhibition of hypoxanthine, 42% of denuded oocytes underwent GVBD after treatment with 100 μM H89 for 30 min. These results suggest PKA involvement in the meiotic arrest of pig oocytes.

Meiotic Resumption of Pig Oocytes by cAMP-Dependent Protein Kinase Inhibitor H89.