Tissue NAD levels and the response to irradiation of cytotoxic drugs.

It has been shown that when (32)P counting from a tumour is continuous peaks in the count rate can sometimes be induced by large doses of nicotinic acid, nicotinic acid, nicotinamide or 3-acetylpyridine, but not by 6-aminonicotinamide. These (32)P counting peaks have been associated with the time of maximal new synthesis of nicotinamide adenine dinucleotide (NAD). Sensitization to irradiation or some cytotoxic drugs has been found at the peak of this new NAD synthesis. The radioprotective agents cysteamine, 2-aminoethylisothiouronium bromide (AET) and serotonin have been found to cause a rapid fall in tissue NAD levels. The results have been briefly discussed.