Ovarian follicles constantly undergo selection and sifting in the process of their development, and many ovarian follicles fall into atresia. Follicular atresia can be prevented by superovulation induction with gonadotropin (GTH), but this treatment causes ovulation of cleaved-unfertilized ova. In this study, the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) reaction was performed in the ovary of mice in which superovulation was induced repeatedly using PMSG/hCG. The TUNEL reaction was positive in oocytes that showed cleavage already in developing follicle and in surrounding granulosa cells. Ovarian follicles developed by superovulation using GTHs include abnormal oocytes with cell fragmentation. This change is remarkably similar to apoptosis.

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