Objective: To assess the effect of repeated gonadotropic stimulations on the developmental potential and growth differentiation factor-9 (GDF-9) expression of mouse oocytes.
Methods: Female 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.
Results: A 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).
Conclusion: Repeated gonadal stimulation decreases the developmental potential of mouse oocytes possibly due to reduced GDF-9 expression.