Effects of timing differences in γ-ray irradiation on ovarian development in rats

This study investigated the effects on ovarian development in adult rats irradiated with γ-rays at fetal, neonatal, weaning, and early sexual maturation. Female Fischer-344 (F344) rats mated with male rats and their F1 offspring were irradiated with a single dose of 0.5 or 2 Gy of γ-rays on gestation day 15 or 19 (GD15 or 19), or postnatal day 5, 20, or 49 (PND5, 20, or 49). F1 females were reared until 27 weeks of age and necropsied. HE-stained specimens of the reproductive organs were prepared for histological examination (n=10-22 per group). The corpus luteum and follicle numbers were also counted in all ovaries. In addition, PCNA-stained specimens were used to count the primordial follicles. At 2 Gy, corpora lutea and follicle depletion was observed in the GD15, PND5, and PND20 irradiation groups. Instead of lost follicles consisting of granulosa cells, numerous tubular structures composed of Sertoli-like cells similar to those found in the testes were noted. In the GD19 group, the ovaries showed less sensitivity to γ-rays. In the PND49 irradiation group, the number of corpora lutea was normal; however, the number of follicles, including primordial follicles, decreased. At 0.5 Gy, the ovaries appeared histologically normal in all the groups; however, the number of follicles decreased in the GD15 and PND5 irradiation groups. In conclusion, we found that the timing of γ-ray irradiation significantly affected subsequent ovarian development, and the degree of change depended on the γ-ray dose.