γ-Radiation-induced follicular degeneration in the prepubertal mouse ovary

Prepubertal mice were whole-body irradiated with a mean lethal dose (LD50) of γ-radiation using a 60Co source with a total dose of 7.2 Gy and a dose rate of 12.0 cGy/min. At day 0 before the irradiation and at day 1, 2, and 3 after the irradiation, the ovaries were collected and the morphological changes were assessed. The ratios (%) of atretic or polymorphonuclear leukocytes (neutrophil)-infiltrated follicles in the largest cross sections were calculated. In the early atretic follicle of the control mouse ovary, both apoptotic and mitotic cells were observed and occasionally neutrophils were infiltrated into the follicle cavity. However, in the atretic follicles 2 days post-irradiation, numerous cell fragments, apoptotic cells and bodies, and especially, a number of neutrophils were observed. In the non-irradiated control, the ratios of atretic follicles were 58.0 ± 8.6 and 27.3 ± 11.2 (mean ± S.E.M.) in antral and preantral follicles, respectively. The ratios of the number of antral and preantral follicles with one or more neutrophils to the total number of atretic follicles were 29.3 ± 12.0. At 2 days post-irradiation, the ratios of atretic follicles were increased to 94.0 ± 3.4 and 86.9 ± 7.6 in antral and preantral follicles, respectively. The ratios of neutrophil-containing follicles among the atretic one were increased to 65.9 ± 11.5 and 57.8 ± 15.4 at 2 and 3 days after the irradiation, respectively. Taken together, the present results show that γ-radiation induces apoptotic and inflammatory degeneration of mouse ovarian follicles. Besides, neutrophils may be involved in the acute atretic degeneration in γ-irradiated mouse ovarian follicles.