X-irradiation and Diphosphopyridine Nucleotide (DPN) Levels in Ascites-tumour Cells and Liver Tissue of Mice

Summary Mice with Ehrlich's ascites tumour received total-body x-irradiation with 900 r-5000 r. Concentrations of oxidized DPN were analysed enzymatically with yeast alcohol dehydrogenase in liver and tumour-cell homogenates 2 hours and 12 hours after irradiation. After 5000 r, tumour cells and liver exhibited but little decrease of DPN: 5 per cent and 7 per cent respectively at 2 hours, and 12 per cent at 12 hours. When animals were irradiated before or after intramuscular administration of nicotinamide (170 mg/kg), significant alterations of steady-state concentrations of DPN were observed. After irradiation, average decreases of DPN in tumour cells and liver were 22 per cent and 27 per cent respectively (2 hours) and 16 per cent and 17 per cent (12 hours). It follows that x-irradiation within the stated dose-range moderately inhibits DPN-synthesis or activates DPN-breakdown. The effect is compensated at normal cellular concentrations of DPN, but is demonstrated if DPN-synthesis is activated by administration of nicotinamide.