Effects of phosphodiesterase inhibitors on spontaneous nuclear maturation and cAMP concentrations in bovine oocytes

It was previously demonstrated that inhibition of cAMP degradation with phosphodiesterase type 3 (PDE3) inhibitors resulted in the maintenance of bovine cumulus–oocyte complexes (COC) and denuded oocytes (DO) in meiotic arrest, while a PDE4 inhibitor was without effect. In this study, different inhibitors of PDE3 and PDE4 were tested for their effects on bovine oocyte nuclear maturation. Bovine COC and DO were cultured in TCM-199+10% fetal bovine serum (FBS) with or without different concentrations of the PDE inhibitors. The PDE3 inhibitor trequinsin significantly increased the percentage of COC remaining at the germinal vesicle (GV) stage after 7 h of culture (19.3, 60.3, and 67.8% GV for control and trequinsin 10 and 50 nM, respectively) while Ro 20-1724 (a PDE4 inhibitor) was without effect. In DO, only trequinsin at 10 nM had a significant effect after 7 h of culture (51.3 and 86.1% GV for control and trequinsin 10 nM, respectively). Trequinsin reduced the percentage of COC reaching the mature phase after 22 h, but was without effect on DO. The protein kinase A (PKA) inhibitor H-89 reversed the inhibitory effect of trequinsin in COC and DO, indicating that inhibition of nuclear maturation by trequinsin involves activation of PKA. Trequinsin increased cAMP concentrations in COC but not in DO, suggesting that cumulus cells may also contain a PDE3 isoenzyme.