Early Effects of X-Irradiation on in Vitro DNA Synthesis in Mouse Spleen

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Abstract
The histological aspects, weight, and nitrogen, deoxyribonucleic acid (DNA), and ribonucleic acid (RNA) contents of spleens were studied 1, 3, and 6 hours after X-irradiation. Free and bound beta-glucuronidase and deoxyribonuclease (DNase) were measured in the same time sequence, and a complete tissue fractionation was performed at 6 hours. These studies were correlated with 3 different determinations measuring different aspects of DNA metabolism, namely (1) the incorporation of C14-thymidine into the DNA of spleen homogenates; (2) the incorporation of Cl4-thymidine monophosphate into purified boiled DNA incubated in the presence of spleen high-speed supernatant; and (3) the phosphorylation of H3-thymidine or Cl4-thymidine monophosphate by spleen supernatant to yield thymidine triphosphate. The results demonstrate: (1) a low incorporation of precursors 6 hours after X-irradiation, probably a consequence of cellular death; and (2) a block in DNA synthesis 1 hour after X-irradiation which cannot be explained by the release of DNase or by an interference with the activity of the enzymes involved in the last steps of DNA synthesis.

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