Effect of Radiation on DNA Metabolism in Various Tissues of the Rat: IV. Early Effects

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Abstract
The effects of ionizing radiation on the incorporation of thymidine-2-C14 into DNA of spleen and small intestine was studied in the rat during the first 2 1/2 hours postirradiation. Relatively short exposures (1 minute) as well as incorportion periods (8 minutes) were used to detect rapid and transient changes in the rate of DNA labeling. The doses ranged from 125 rep to 4600 rep of Co60 gamma-radiation to the whole body. In both organs the incorporation of C14 into DNA was immediately depressed. At the lower dose, a temporary reversal was observed, followed by a progressive and sustained drop in the incorporation. The effect of irradiation on the phosphorylation of thymidine to thymine nucleotides in the spleen was not of a sufficient magnitude to account for the decreased rate of incorporation of C14 into the DNA of that organ. The results do not permit any conclusion as to whether the immediate effect observed represents a direct effect on DNA synthesis. In later postirradiation periods, delayed onset of DNA synthesis and cell death may account for the observed effects.