DNA-synthesis in the Spleen of Mice after Whole-body X-irradiation and Its Modification by 5-hydroxytryptamine and NADH

SummaryThe rate of 3H-thymidine incorporation into DNA and the DNA content have been measured in the spleen of mice. After whole-body X-irradiation, DNA synthesis decreases rapidly after radiation doses of 15 to 150 R. When the dose—dependence of DNA synthesis is plotted semilogarithmically three hours after irradiation a straight line results; six hours after irradiation a curve with a shoulder and a D0 of 54 R. It is assumed that this radiosensitive part of the dose—effect curve represents DNA synthesis in medium-sized lymphocytes. The levels of adenine nucleotides are not changed under these conditions.NADH and 5-hydroxytryptamine depress DNA synthesis in the spleen for a short period. When these substances are injected before irradiation the initial reduction of DNA synthesis is modified but the recovery starts earlier. Also the DNA content does not decrease so much under these conditions.