The urinary excretory ratio of nicotinamide catabolites was associated with the conversion ratio of tryptophan to nicotinamide in growing rats fed a niacin-free 20% casein diet.

Weaning rats were fed a niacin-free 20% casein diet. Twenty-four-h-urine samples were collected, and nicotinamide and its catabolites were measured. A correlation was found between the urinary excretory ratio of nicotinamide catabolites (N(1)-methyl-2-pyridone-5-carboxamide + N(1)-methyl-4-pyridone-3-carboxamide)/N(1)-methylnicotinamide and the tryptophan-nicotinamide conversion ratio during growing period of the rats. This indicates the possibility that the conversion ratio can be deduced from the excretory ratio.