Residual Injury Induced in the Erythropoietic System of the Rat by Periodic Exposures to X-Radiation

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Abstract
Much higher single X-ray exposures were necessary to cause the depressions in Fe59 uptake observed in rats irradiated repeatedly with 300 r and 400 r. In contrast to marrow changes, peripheral erythroid decreases were small until the last irradiation period, indicating that the quantity of stem cells available for erythrocyte production must greatly exceed the number required in the daily red cell turnover. It must be questioned whether rats with an impaired erythrocyte proliferation system could respond to emergency situations as well as normal animals. Irradiation accelerated the appearance of mammary tumors. The appearance in the nonirradiated animals was at a much more advanced age. Rats repeatedly exposed to X-ray doses of 300 r or 400 r at 3-month intervals showed diminution in Fe59 incorporation into erythrocytes after each dose. The results for the total rat population indicated a heterogeneity in response of their erythroid precursors to the effect of X-radiation. When these populations were regrouped into subgroups based on whether they survived three, four, or five irradiation exposures, it was observed that the Fe59 incorporation, on the average, decreased exponentially with increasing number of exposures.