The Effect of a Single Systemic X-Irradiation of the C57BL Mouse on the Nucleodepolymerases of the Thymus'

In a study of thymic nucleodepolymerases in radiation-induced thymoma in the C57BL mouse, we noted that early postirradiation changes in activity appeared to be independent of the carcinogenic process. A detailed study of these early changes with low doses of X-irradiation was carried out as described in this paper. Nucleodepolymerase changes in mammalian tissues after whole-body X-irradiation have been reported. After 600 r to rats, there were variable changes in acid and alkaline RNase2 concentrations in whole-liver homogenates and liver mitochondria and depression of a soluble inhibitor tested with pancreatic RNase. These changes were noted 1 to 5 days after treatment (1). A twoto threefold increase in acid DNase concentration of spleen was found 24 hours after doses of 50 to 500 r to rats. The increase was not observed at earlier periods tested, and there was no change in spleen content (2, 3). Finally, increases in urinary (4) and serum (5) acid and alkaline DNases have been observed after 700 r to rats. The response of other enzymes of spleen and thymus to whole-body irradiation has been reviewed by DuBois and Petersen (6). Thymic concentration of various respiratory enzymes showed little or no change. The most marked effect observed was an increase in concentration of adenosinetriphosphatase after relatively small doses of X-irradiation to the rat. The increase was maximal in both spleen and thymus 3 to 5 days postirradiation with doses as low as 50 r in spleen and 100 r in thymus. It was two to three times normal in both tissues after 200 r (6). After 650 r to the mouse, however, splenic content of adenosinetriphosphatase was below normal from about 4 hours to 18 days (7).