Lifetime reproductive performance of mice exposed as embryos to x-irradiation.

Abstract

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 6½, l0½, l4½ and l7½ 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 6½, 10½, and 14½ 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 6½, 17½, 14½, and l0½ days. The incidence of sterile matings was pronounced only following 160 r or 320 r at 17½ days. Significant effects on reproduction due to genotype and sex were observed at all ages. Survivors of irradiation at 6½ days had normal fertility and fecundity. A dose of 80 r at 10½ days reduced reproductivity to 76% of control values. Significant effects due to levels of irradiation were observed at both l4½ and 17½ days. Mice irradiated with 160 r at 14½ days produced only 72% as many progeny as controls. Following irradiation with 160 r at l7½ days, irradiated mice produced 83% as many progeny as controls. With a dose of 320 r at 17½ 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 17½. 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.