LIFETIME REPRODUCTIVE PERFORMANCE OF MICE EXPOSED AS EMBRYOS TO X-IRRADIATION

¹ Department of Zoology, Colorado State University, Fort Collins, Colorado 80521

1. Lifetime reproductive performance was observed in mice that had been irradiated at different stages of embryological development. Three genetically differentiated inbred strains of mice, BALB, K, and S, and all their possible hybrids, including reciprocals, were used. Pregnant females were exposed to single whole-body 250 pkv x-ray dosages from 20 r to 320 r on 6, l0, l4 and l7 days gestation, as timed from the appearance of a vaginal plug. Efforts were made to obtain two mice of each sex and inheritance type for each of the irradiation dose-embryological age treatment combinations. No progeny or not sufficient progeny were obtained following irradiation with 160 r or 320 r at embryological ages of 6, 10, and 14 days of age. At 75 days of age treated mice were outcrossed to mice of the Z strain, and matings were maintained for the lifetime of the treated mice.

2. Adult reproductive performance was found to be related both to the age of the embryo at the time of irradiation and the level of irradiation. The embryological ages in order of increasing sensitivity were 6, 17, 14, and l0 days. The incidence of sterile matings was pronounced only following 160 r or 320 r at 17 days. Significant effects on reproduction due to genotype and sex were observed at all ages. Survivors of irradiation at 6 days had normal fertility and fecundity. A dose of 80 r at 10 days reduced reproductivity to 76% of control values. Significant effects due to levels of irradiation were observed at both l4 and 17 days. Mice irradiated with 160 r at 14 days produced only 72% as many progeny as controls. Following irradiation with 160 r at l7 days, irradiated mice produced 83% as many progeny as controls. With a dose of 320 r at 17 days the incidence of sterility was 67% and progeny production fell to 21%

3. Genetic differences in the response of the fetal reproductive system were most evident following irradiation on day 17. Inbred progeny appeared to be more radiosensitive than hybrid progeny. The incidence of sterility after 320 r was 100% in inbreds compared to 50% for hybrids. Fecundity following 160 r was reduced in inbreds, but remained near normal in hybrids.