Retinoic acid effects on nuclear maturation of bovine oocytes in vitro

In the present study, the effect of all-trans retinoic acid (t-RA) administration during in vitro maturation (IVM) on bovine oocytes maturation was determined. Concentrations of t-RA (RA; 0, 0.25, 0.5 and 1 mu M) and 0.1% ethanol (vehicle) were included in the maturation medium. Ovaries collected from the local abattoir were transported to the laboratory in in 0.9% NaCl with 100 IU/ml penicillin and 100 mu g/ml streptomycin at 30 - 35 degrees C within 1-2 h after collection. The oocytes of antral follicles, 2 to 8 mm in diameter, were recovered by aspiration. After preliminary evaluation, the oocytes were selected and washed four times in HEPES-TCM 199 supplemented with 2% FBS, 0.2 mM sodium pyruvate, 100 IU/ml penicillin and 100 mu g/ml streptomycin. Then 10 cumulus-oocyte complexes (COCs) were subjected to each droplet of maturation medium and incubated at 38.5 degrees C, 5% CO2 and 95% humidity for 24 h. Maturation medium was bicarbonate-buffered TCM199 supplemented with 10% FBS, 0.2 mM sodium pyruvate, 5 mu g/ml bovine FSH, 0.01 IU/ml bovine LH, 100 IU/ml penicillin and 100 mu g/ml streptomycin. Results show different concentrations of t-RA have no effect on cumulus expansion. The rate of oocytes developing to the MII stage compared to control, vehicle, and 0.25 mu M groups was significantly increased with 1 mu M t-RA treatment (p<0.05). In conclusion, 1 mu M retinoic acid significantly increased the bovine oocyte maturation in the commercial TCM199 medium.