Comparison of The Urinary Excretion of Niacin and Its Metabolites in Various Mammals

Abstract

Niacin metabolism in omnivora, carnivora and herbivora was compared with high-performance analysis of urine. In omnivora (ten kinds of primates and pig), excreted amount of N^1-methyl-2-pyridone-5-carboxamide (2-Pyr) occupied 60-90% of the total urinary excretion of NiA-NH_2 and its metabolites. So, it was found that NiA-NH_2 was catabolized as follows in omnivora; NiA-NH_2→N^1-methylni-cotinamide (MNA)→2-Pyr. In carnivora (cat, dog, lion and tiger), the urinary excretion of MNA occupied above 90% of the NiA-NH_2 and its metabolites totally excreted and the oxidized forms of MNA such as 2-Pyr and N^1-methyl-4-pyridone-3-carboxamide were very slight. So, NiA-NH_2 was found to be catabolized as follows in carnivora; NiA-NH_2→MNA. In herbivora (four kinds of artiodactyla and horse), the urinary excretion of NiA-NH_2 occupied 80-100% of the total urinary excretion of NiA-NH_2 and its metabolites. Thus, it was found that NiA-NH_2 was hard to be catabolyzed in herbivora. In all mammals examined here, the urinary excretion of NiA, NuA and NiA-NH_2 N-oxide was below the limit of detection.