Differentiation as a Determinant of the Reaction of Rat Embryos to X-Irradiation.

Abstract

X-irradiation of rat embryos on the 8th day of gestation had a more limited effect on subsequent development than similar treatment on the 9th or 10th days. The only residual effect after doses of 12.5 to 100 r on the 8th day was retardation of growth. Exposure to comparable doses on the 9th and 10th days results in the development of malformations and in an increase in mortality, as well as in retardation of growth. This difference in reactivity appears to be dependent upon the presence or absence of cellular differentiation within the embryos at the time of irradiation.