EFFECTS OF X-IRRADIATION UPON POSTNATAL GROWTH IN THE MOUSE

¹ Department of Genetics, Iowa State University, Ames, Iowa

1. The effect of x-irradiation of mouse embryos upon their postnatal development was measured by several responses: body weight changes from birth to maturity, lifetime fecundity, and total lifespan. The body weight responses are reported in this paper. Three genetically differentiated inbred strains of mice, Ba, 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 64, 10, 14, and 17 days gestation, as timed from the appearance of a vaginal plug. In addition the study included progeny irradiated on the day of birth without any irradiation of the maternal organism. Postnatal growth was followed from birth to 75 days of age, individuals having been weighed at birth, 12, 26, 40, 60 and 75 days.

2. Body weights were adjusted by making use of the pooled regression coefficient of body weight on litter size over all treatments. Body weight response was found to be dependent on both level of irradiation and embryological age at irradiation. The embryological ages in order of increasing sensitivity were 6, 17, 14 and 10 days. Body weight response was found also to be markedly dependent upon the age at which observations were recorded. In those treatments that produced significantly lowered body weights the maximum effect was not found usually until 40 days postpartum. Growth effects appeared to be permanent since there was little recovery evident by 75 days. Evaluation of these results emphasizes the importance of considering both immediate and delayed effects in assessing damage induced by embryonic irradiation.

3. Growth differences following embryonic irradiation were found to be under a strong genetic influence. Genetic differences in response to the induction of growth retardation were thought to be expressed as a result of genetically determined differences in recovery from disturbed physiological activities and differences in developmental age of embryos at the time of irradiation.