Fundamental significance of specific phosphodiesterases in the control of spontaneous meiotic resumption in porcine oocytes

The meiosis of mammalian oocytes begins during the fetal life and stops at the dictyate stage. This study has assessed the role of specific phosphodiesterase (PDE) inhibitors on the control of meiotic resumption in porcine oocytes investigating the influence of PMSG-hCG and cAMP stimulation. Cumulus-oocytes complexes (COCs) and denuded oocytes (DOs) were collected from gilt ovaries obtained at a local slaughterhouse. Oocytes were cultured in NCSU23 with different PDE inhibitors. The EC(50) for oocytes maintained in germinal vesicle (GV) stage was evaluated using different doses of both cilostamide (CIL), PDE3 inhibitor and 3-isobutyl-1-methylxanthine (IBMX), a nonspecific PDE inhibitor. In presence of PMSG-hCG, meiotic resumption is observed after 24 hr of culture. Both CIL and IBMX reversibly blocked meiotic resumption. In absence of PMSG-hCG, meiotic resumption is reduced after 24 hr of culture. After 48 hr of culture, only CIL significantly blocked meiotic resumption. Still in absence of PMSG-hCG, significant effect of treatment was only observed in COCs using the combination of CIL and rolipram (PDE3 and PDE4 inhibitor, respectively) compared to the use of IBMX. To assess the contribution of cAMP synthesis, a low dose of an adenylyl cyclase (AC) stimulator, forskolin, has been used in combination with CIL showing a significant effect of this combination. In CIL-treated COCs and DOs, significant higher percentages of oocytes were maintained in GV stage when cultured in combination with forskolin instead of PMSG-hCG. In conclusion, these results demonstrate that the control of meiotic resumption in porcine oocytes is highly regulated by cAMP. Both the degradation by specific PDE3 enzyme and the synthesis by an active AC are highly involved.