Prenatal Survival of Mice Irradiated with Fission Neutrons or 300kVp X-rays during the Pronuclear-zygote Stage: Survival Curves, Effect of Dose Fractionation

Summary Mouse embryos were irradiated or sham-irradiated in utero during the pronuclear-zygote stage and examined 16 days later. A simple exponential equation closely approximates the relation between surviving fraction of embryos and absorbed dose up to the highest dose used (20 rads of neutrons, 100 rads of X-rays). This suggests (1) that in the dose-range studied, pronuclear-zygote inactivation was predominantly a single-event process (i.e. embryo death resulted from passage of one ionizing particle) with either radiation, and (2) that the relative biological effectiveness of the neutrons (approximately 4·5) was close to the low-dose limiting value. D0 was 19 rads for neutrons and 87 rads for X-rays. With increasing radiation dose, not only did prenatal mortality increase but the embryos also died earlier in development. Dose-fractionation experiments suggest that irradiation of the early pronuclear zygote impeded its progression to a less radiosensitive phase.