The Indirect Effect of X rays on the Synthesis of Nucleic Acidin vivo

Abstract

1. The synthesis of thymo- and ribo-nucleic acid (in the Jensen rat sarcoma) has been studied in irradiated tumours and in other tumours in an irradiated animal, which are themselves not receiving irradiation. 2. This “indirect” effect of radiations on nucleic acid synthesis has been demonstrated for both ribo- and thymonucleic acid. 3. In animals killed 1 hour after irradiation, the direct and indirect effects are both large. Thymonucleic acid synthesis is reduced to about 25 per cent. of the normal in the directly irradiated tumour, and about 50 per cent. of the normal in the screened tumour. The ribo-nucleic acid renewal is affected similarly, but to a much smaller extent. 4. When P³² is injected about 2 hours after irradiation and the animal killed 1 hour later, the ribo-nucleic renewal is nearly normal in all tumours. The thymo-nucleic acid synthesis of the screened tumour is nearly normal, and in the irradiated tumour is about 60 per cent. of normal. When injected at 4 hours after irradiation and killed 1 hour later, the thymo-nucleic synthesis is found to be proceeding at a normal rate. 5. Counts indicate that the dose of X radiation used produces a considerable amount of abnormal mitosis, while no normal mitosis is taking place 5 hours after irradiation.