REPRODUCTIONRESEA CH Effects of long-term in vitro exposure to phosphodiesterase type-3 inhibitors on follicle and oocyte development

Germinal vesicle (GV)-stage oocytes retrieved from antral follicles undergo nuclear maturation in vitro, which typically occurs prior to cytoplasmic maturation. Short-term culture with meiotic inhibitors has been applied to arrest oocytes at the GV stage aiming to synchronize nuclear and ooplasmic maturity. However, the results obtained are still far from the in vivo situation. In order to acquire competence, immature oocytes may require meiotic arrest in vitro for a more extended period. The phos-phodiesterase type 3-inhibitor (PDE3-I) is a potent meiotic arrester. The effects of a prolonged culture with PDE3-I on oocyte quality prior to and after reversal from the inhibition are not known. This study tested the impact of long-term in vitro exposure of two PDE3-Is, org9935 and cilostamide, on oocytes using a mouse follicle culture model. The results showed that PDE3-I (maximum of 10mM) during a 12-day culture of follicle-enclosed oocytes did not alter somatic cell proliferation, differentiation or follicle survival. In addition, the steroid production profile was not significantly modified by a 12-day exposure to PDE3-I. The recombinant human chorionic gonadotrophin/recombinant human epidermal growth factor stimulus induced a characteristic normal progesterone peak of luteinization and normal mucification of the cumulus cells, while the enclosed oocyte remained blocked at the GV stage. In vitro maturation of denuded or cumulus-enclosed oocytes derived from org9935- or cilostamide-exposed follicles progressed through meiosis and formed morphologically normal meiotic spindles with chromosomes properly aligned at the equator. In conclusion, long-term culture with PDE3-I was harmless to somatic cell function, differentiation, oocyte growth and maturation. Our results suggested that PDE3-I can be applied when extended oocyte culture is required to improve ooplasmic maturation