MAINTENANCE OF MEIOTIC ARREST BY INCREASING [CAMP](I) MAY HAVE PHYSIOLOGICAL RELEVANCE IN BOVINE OOCYTES

Invasive adenylate cyclase (iAC) reversibly inhibits spontaneous matur ation of cumulus-enclosed bovine oocytes by increasing the intracellul ar concentration of cAMP, [cAMP](i). In this study, physiological aspe cts of maintaining meiotic arrest in bovine oocytes by iAC were invest igated. The maintenance of germinal vesicle arrest by IAC in both cumu lus-enclosed and denuded bovine oocytes was concentration dependent (r (2) = 0.857). Denuded bovine oocytes were more sensitive to maintenanc e of meiotic arrest by iAC then were cumulus-enclosed oocytes. At the highest concentration, 70% of the cumulus-enclosed and 90% of the denu ded bovine oocytes were maintained in meiotic arrest. The iAC increase d [cAMP](i) in both intact cumulus-oocyte complexes and enclosed oocyt es in a concentration-dependent manner (r(2) = 0.795). Cumulus-enclose d oocytes maintained in meiotic arrest by iAC retained developmental c ompetence when subsequently cultured in iAC-free medium and then ferti lized. The [cAMP](i) in bovine complexes decreased precipitously upon release from follicles and remained low for the next 125 min. However, the [cAMP], of the enclosed oocytes did not change. Bovine oocytes co mmit to undergo meiosis in a progressive manner. Approximately 10% of the oocytes were already committed when aspirated. This proportion inc reased to 40% at 2 h and 70% at 5 h. Use of two inhibitors of cAMP-dep endent protein kinase A provided further evidence that cAMP functions in mediating meiotic arrest in bovine oocytes. Bovine oocytes, therefo re, are sensitive to different cAMP concentrations, and are developmen tally competent after iAC-induced arrest, and complexes containing ooc ytes exhibit a decrease in [cAMP](i) before spontaneous maturation. Th ese results suggest that maintenance of meiotic arrest by iAC is accom plished through modulation of cellular machinery, and regulation of oo cyte maturation by [cAMP](i) may be physiologically relevant.