Effect of X-Irradiation on DNA Synthesis in the Uterine Epithelium

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Abstract
The effects of X-irradiation on the presynthetic and synthetic phases of the [mouse] uterine epithelial cells with respect to DNA synthesis were investigated by varying the timing of irradiation and tritiated thymidine injection relative to the time of estrogen administration. Whole-body doses of 100 to 400 rads at a time when the epithelium was in the presynthetic phase delayed most of the cells from making the transition from the G1 phase to the S phase, whereas 2000 rads prevented them from ever making the transition during the observational period. Whole-body doses of 200 to 2000 rads at a time when the epithelium was in the synthetic state reduced DNA synthesis in S phase cells by about one-half. These results suggest that the mechanisms affected by irradiation of S phase cells are different from those affected in the presynthetic period. The different possible natures of G1 and S effects are discussed.