Metabolism of nicotinic acid and related compounds in man and rat

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Abstract
The excretion of metabolites by man and the rat after admn. of nicotinic acid, nicotinamide and tryptophan was studied by paper- chromatographic technics which did not allow detection of N1-methyl-2-pyridone-5-carbonamide. After a dose of 100 mg. of nicotinic acid to man, the main nicotinyl metabolites in the urine were in decreasing order, nicotinuric acid, N1-methylnicotinamide and nicotinamide. Nicotinic acid appeared in the urine only when flushing of the skin and other vasodilatory symptoms occurred. In the rat nicotinic acid appeared consistently in the urine, but otherwise the pattern of excretion remained the same as in man. Admn. of 100 mg. nicotinamide to human subjects caused increased excretion of only N1-methylnicotinamide and nicotinamide. Rat urine contained also an increased amt. of nicotinic acid. Nicotinuric acid was not excreted by either sp. After ingestion of 3 g. of L-tryptophan human urine showed an increase in the excretion of N1-methylnicotinamide; rat urines showed also an increased output of nicotinic acid. In human urine kynurenic acid, 3-hydroxyanthranilic acid, kynurenine and tryptophan were identified. Admn. of 100 mg. of quinolinic acid to normal rats resulted in an increased excretion of N1-methyl-nicotinamide and nicotinic acid, while rats deficient in nicotinic acid showed no such rise. In urines from undosed human subjects, microbiological technics instead of the chemical procedure had to be used to detect on chromatograms the tertiary nicotinyl compounds because of the small amts. of nicotinyl derivatives present. The urines contained a small amt. of nicotinamide and of N1-methylnicotinamide. Urines from undosed rats, both deficient and normal, contained N1-methylnicotinamide, nicotinamide and nicotinic acid.