“The formation of the upper metabolites of tryptophan to niacin such as anthranilic acid, …-hydroxyanthranilic acid were not affected, but the quinolinic acid and beyond, such as nicotinamide , N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and N1 -…-3-carboxamide, were significantly reduced by the administration of orotic acid.”