The in vivo conversion ratio of N-methylnicotinamide (NMN) to N-methyl-2-pyridone-5-carboxamide (2-PY) and N-methyl-4pyridone-3-carboxamide (4-PY) as a parameter for the estimation of aldehyde oxidase level in rats was examined. NMN and its pyridones (2-PY and 4-PY) are usually detected in the urine of rats. When we measured the ratio of the amount of pyridones to the total amount of NMN and py...