Comparative Effect of Tryptophan, Niacin, and Nicotinamide in Forming Liver Pyridine Nucleotides.

Changes in the level of liver pyridine nucleotides (PN) of rats were studied at various times following the administration by stomach tube of equimolar amounts of tryptophan, niacin, or niacinamide. Tryptophan was observed to be equally effective as a PN precursor as equimolar amounts of niacin, whereas niacinamide produced significantly higher levels of liver PN than either tryptophan or niacin. When incorporated directly into the ration, however, niacin and tryptophan were again equivalent as PN precursors whereas, under these conditions, nia-cianamide was a slightly less efficient PN precursor than niacin or tryptophan.