Nuclear and cytoplasmic maturation of in vitro matured human oocytes after temporary nuclear arrest by phosphodiesterase 3-inhibitor

BACKGROUND: The use of hormones for controlled ovarian stimulation results in follicular heterogeneity, with oocytes at diverse stages of nuclear and cytoplasmic development. This study evaluated the impact of temporary nuclear arrest by a specific phosphodiesterase 3-inhibitor (PDE3-I), cilostamide, on nuclear and cytoplasmic maturation of cumulus-free germinal vesicle (GV) human oocytes from controlled ovarian stimulated cycles. METHODS: GV oocytes (n = 234) were cultured in: (i) medium without the inhibitor (control); (ii) medium supplemented with 1 mu M cilostamide and (iii) medium supplemented with 10 mu M cilostamide. Oocytes in groups (ii) and (iii) were exposed to cilostamide for 24 h. The PDE3-I was subsequently removed by transfer of oocytes to fresh in vitro maturation (IVM) medium and the reversibility of GV arrest was assessed during IVM culture for maximum 48 h. RESULTS: Cilostamide (1 and 10 mu M) could maintain > 80% of the oocytes at the GV stage, without affecting subsequent maturation to metaphase II. Oocytes exposed to 1 mu M cilostamide were more likely to have normal bipolar spindles with aligned chromosomes than control oocytes (P < 0.05). When GV chromatin configurations before and after arrest were compared, a significantly higher proportion of oocytes had acquired a nucleolus completely surrounded by a rim of highly condensed chromatin (P < 0.05). CONCLUSIONS: Temporary nuclear arrest of human GV oocytes with PDE3-I proved to be beneficial for obtaining normal spindle and chromosome configurations after IVM. It resulted also in synchronization within the population of GV oocytes.