Low-dose effects of X-rays and negative pions on the pronuclear zygote stage of mouse embryos.

Mouse embryos in the pronuclear-zygote stage (day 0 of gestation) were irradiated with 13.5 rad of 140kV X-rays or negative pions. On day 13 the fetuses were examined for developmental anomalies such as intrauterine death, growth retardation and malformations. Significant decreases in the percentage of normal implantations were obtained with peak pions (high LET) and X-rays, whereas the effect of plateau pions was less obvious. Irradiation with peak pions was more effective than with X-rays by a factor of about 1.7.