Effects of butyrolactone-I on GVBD in bovine oocytes and subsequent maturation, fertilization and development in vitro

In Experiment 1, bovine cumulus oocyte complexes (COCs) were preincubated for 24 h in M199 supplemented with 25-100 muM BL-I, an inhibitor of cdc2 kinase activity. Half of the COCs were fixed to assess rates of germinal vesicle breakdown (GVBD), and the rest were cultured for a further 20 h without BL-I to investigate whether BL-1 affects their meiotic competence. In Experiment 2, COCs treated with BL-I for 24 h or 48 h were matured (IVM), fertilized (IVF) and then cultured in vitro (IVC) for 8 days. Oocytes exposed to 100 muM BL-I showed a significantly higher rate of germinal vesicle (GV) (86%) stage than the others (4-72%). Oocytes exposed to 100 muM BL-I for 48 h showed equally high GV (95%) stage and maturation (84%) rates compared to oocytes treated for 24 h and control oocytes with no treatment. However, they showed significantly lower normal fertilization (27%), cleavage (27%) and blastocyst formation (6%) rates than oocytes treated for 24 h (66, 69 and 42%, respectively) and control oocytes (65, 75 and 42%, respectively). The results indicate that BL-I can reversibly inhibit GVBD of bovine oocytes for at least 24 h but not for 48 h without compromising subsequent developmental competence after IVM-IVF-IVC.