EFFECTS OF PRENATAL X-IRRADIATION ON DEVELOPMENT AND POSTNATAL VIABILITY OF INBRED AND HYBRID MICE

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

1. Developmental malformations and effects on postnatal viability were measured in inbred and hybrid mice that had been irradiated at different stages of embryological development. Three genetically differentiated inbred strains of mice, BALB, K, and S, and their six possible types of hybrids, including reciprocals. were used. The design for these studies was factorial. There were five levels of irradiation: 0, 20, 80, 160, and 320r; five embryological stages: untreated, 6, 10 14, and 17 days of gestation; two sexes; and mice of nine different inheritance types. Pregnant females were exposed to single whole-body 250 pkv x-rays on a specified day of gestation as timed from the appearance of a vaginal plug. Malformations were scored at birth and postnatal mortality was followed through 75 days of age.

2. Morphological anomalies observable at birth were found only after irradiation at 10 days gestation. Anomalies were observed after doses of 80r or more. Neonatal mortality also was highest following irradiation at 10 days. The LD₅₀ at birth was found to be between 80 and 160r, with a dose of 320r causing all progeny to be stillborn.

3. A differential response both in the induction of malformations and in the incidence of neonatal deaths was found between inbred and hybrid genotypes. Following treatment with 160r at 10 days there was 64 per cent abnormal and 100 per cent stillborn progeny among the inbreds compared to 29 per cent abnormal and 64 per cent stillborn among the hybrids.

4. Effects of prenatal irradiation on postnatal survival to 60 days were at a minimum after treatment at 6 days gestation, reached a maximum following irradiation at 10 days, and then declined at 14 or 17 days. No consistent patterns of survival differences between males and females and level of irradiation and embryological stage at the time of treatment was observed.

5. Among the control or non-irradiated mice, inbred progeny suffered a higher mortality than the hybrids especially during the first few days after birth. In those treatments which produced a significant increase in postnatal mortality, inbred genotypes responded to a greater degree than did hybrid genotypes.