Induction of malformations by X-ray exposure of various stages of the oogenesis of mice.

We studied the effects of ionizing radiation (X-rays, 0-3 Gy, dose rate 1 Gy/min) on various stages of oogenesis of a mouse strain (HLG/Zte) that had been shown previously to respond with an increased number of malformations after radiation exposure of preimplantation stages. Like the results obtained with preimplantation stages, we observed a statistically significant increase in the number of malformed fetuses (exclusively gastroschises) on day 19 of gestation, when oocytes within 1-4 weeks before ovulation were exposed to 2 or 3 Gy. Less mature oocytes were killed by radiation doses of 0.5 Gy and higher. In addition to the increased frequency of malformations, we found a dose-dependent increase of lethal effects (affecting either oocytes or specific gestational stages) and of runts ('dwarfs').