Role of estradiol-17beta on nuclear and cytoplasmic maturation of pig oocytes

The role of estradiol-17beta on nuclear and cytoplasmic maturation of pig oocytes was investigated in the present study. To determine the estradiol effect, oocytes were cultured for 42 h in a steroid free medium composed of mTCM-199 supplemented with LH, FSH and 10% charcoal extracted follicular fluid. Estradiol receptor (ER), detected by a binding assay, were present in cumulus cells and oocytes during maturation with higher levels observed at 24 h of culture in the oocytes and at 36 h in the cumulus cells. To block estradiol action an antiestrogen (1-p-dimethylaminoethoxyphenyl-1,2-diphenyl-1-butene (tamoxifen)) was added to the maturation medium at various concentrations. The percentage of treated oocytes that underwent nuclear maturation was similar (P>0.05) to the control group. Cytoplasmic maturation, determined by the ability to form female pronucleus (FPN) and male pronucleus (MPN), was not different (P>0.05) among all groups. The presence of 4-hydroxy-4-androstene-3-17-dione (4-OHA) also did not influence nuclear (P>0.05) or cytoplasmic maturation (P>0.05). The results suggest that estradiol is not involved in maturation of pig oocytes. However, the present experiment used pronuclei formation as the endpoint, no studies were done in regard to estradiol's effects on the embryonic development.