Ovary tumors in NMRI mice subjected to fractionated X-irradiation during fetal development.

Fractionated X-irradiation of pregnant mice was performed either during late organogenesis (gestational days 11-13), during the early fetal period (g.d. 14-16), or during both periods (g.d. 11-16). The offspring were observed for 39 months. A significant increase of ovary tumor frequency was observed with 3 X 1.2 Gy, applied either in late organogenesis or in the early fetal period. Lower X-irradiation doses were ineffective in these periods with respect to ovary tumor development. A sharp increase in ovary tumor frequency resulted after irradiation with 6 X 0.8 Gy or 6 X 1.2 Gy. The highest incidence of ovary cysts was observed after 3 X 1.0 Gy or 3 X 1.2 Gy on g.d. 11-13, while the frequency of these cysts was lowest in the animals irradiated six times, which, however, showed a high ovary tumor frequency. Autoradiography of the fetal ovaries either 1 or 6 days after irradiation at the late organogenesis stage revealed a persistent depression of this organ's proliferation rate throughout pregnancy. This may be consistent with the low tumor inducibility after X-irradiation in this period.