OBJECTIVETo assess the effect of repeated gonadotropic stimulations on the developmental potential and growth differentiation factor-9 (GDF-9) expression of mouse oocytes.

METHODSFemale Kunming mice were treated with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG) for 3 times, and the control mice were treated with normal saline. The two groups of mice were both stimulated subsequently to obtain the mature oocytes. Immunocytochemical staining was employed to evaluate GDF-9 expression in the oocytes. The oocytes were then inseminated and cultured till the formation of blastocysts to compare the cleavage rate and blastocyst formation rate between the groups.

RESULTSA total of 253 mature oocytes were obtained in the repeated stimulation group, with a mean of 11.5 oocytes from each mouse; 521 mature oocytes were obtained in the control group with a significantly greater mean number of 32.6 from each mouse (P<0.05). The average optical density and integrated optical density for GDF-9 expression were significantly lower in the oocytes in repeated stimulation group than in the control group (P<0.05 and 0.01, respectively). After insemination, the cleavage rate were comparable between repeated stimulation group and the control group (85.6% vs 88.8%), but the blastocyst formation rate was significantly lower in repeated stimulation group (20.8% vs 35.2%, P<0.01).

CONCLUSIONRepeated gonadal stimulation decreases the developmental potential of mouse oocytes possibly due to reduced GDF-9 expression.