Effect of dietary protein levels on the urinary excretion of nicotinamide and its metabolites in rats.

Abstract

Male rats of the Wistar strain (seven weeks old) were fed adlibitum with a 10%, 20% or 40% casein diet (these diets contained sufficient nitocinic acid of 6 mg per 100 g of diet) for 20 days. Urine was collected for the last 2 days, and the urinary excretion of nicotinamide, A^-methylnicotinamideA^-methyl^-pyridone-S-carboxamide (2-py) and A^-methyM-pyridone-S-carboxamide (4-py) was measured using the most reliable determination methods with a high-performance liquid chromatograph. The urinary excretion of nicotinamide and 2-py was about the same in the three groups. The urinary excretion of 4-py increased with increasing dietary protein levels, contrary to MNA, which decreased with increasing dietary protein levels. The total urinary excretion of nicotinamide, MNA,2-py and 4-py was about the sameamountin the three groups. The contents of total nicotinamide and MNAin the liver decreased with increasing dietary protein levels, all these results being inconsistent with the established theory.