EFFECTS OF X-IRRADIATION UPON POSTNATAL GROWTH IN THE MOUSE

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Abstract
The effects of X-irradiation upon the postnatal development of mouse embryos were 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 or 320 r at various times after impregnation. In addition, mice irradiated on the day of birth without any irradiation of the maternal organism. Body weight response was dependent on both level of irradiation and embryological age at irradiation. The embryological ages in order of increasing sensitivity were 6 1/2, 17 1/2, 14 1/2, and 10 1/2 days. Body weight response was also markedly dependent upon the age at which observations were recorded. The maximum effect was usually seen 40 days postpartum. Growth effects were permanent; 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. 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.

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