Effect of X-Radiation on DNA Metabolism in Various Tissues of the Rat: III. Retention of Labeled DNA in Normal and Irradiated Animals

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Abstract
The retention of DNA (deoxyribonuclelc acid) previously labeled with thymidine-2-C14 in vivo has been studied in normal and in irradiated rats. In the normal rats average turnover times have been calculated for the more active cells in thymus, spleen, bone marrow, and small intestine. The data also provided a rough estimate of the migration time of the epithelial cells in the small intestine. Irradiated rats were given 100 or 400 r 3 or 24 hours after the injection of radioactive precursor. The specific activity of the DNA retained in the different organs indicated that labeled and unlabeled cells were lost in a random manner. With respect to the loss of cells from these organs, the dividing and nondividing cells are, equally sensitive to radiation. There was, furthermore, no indication of cyclic changes in this sensitivity, nor was the cell loss related to any specific time of the division cycle.