抄録
When a large amount of nicotinamide (500 mg per kg body weight) was intraperitoneally injected into rats, the ratio of N1-methyl-4-pyridone-3-carboxamide (4-py) to N1-methyl-2-pyridone-5-carboxamide (2-py) excretion steeply decreased until 24 hr after injection, then this excretion ratio recovered gradually and returned to the normal level by day 4 after injection. The ratio of 2-py plus 4-py to N1-methylnicotinamide (MNA) excretion was also decreased steeply by a pharmacological dose of nicotinamide. This ratio decreased until 24 hr after injection; after that time it recovered gradually and returned to the normal level. The rats were killed 24 hr after the injection and the activities of nicotinamide methyltransferase, 2-py forming MNA oxidase, and 4-py forming MNA oxidase in liver were measured. The activity of nicotinamide methyltransferase was slightly increased by a pharmacological dose of nicotinamide but the activities of 2-py forming MNA oxidase and 4-py forming MNA oxidase in the injected group were 45 % and 7 % of normal, respectively. From these results, it was found that the decreased ratios of 4-py to 2-py excretion and of 2-py plus 4-py to MNA excretion were attributed to the changes of the two MNA oxidase activities by a pharmacological dose of nicotinamide. The addition of nicotinamide to the standard assay reaction mixture of 2-py forming MNA oxidase and 4-py forming MNA oxidase did not affect the 2-py and 4-py formation activities.
