Effects of Protein-Free Diet Feeding or Starving on the Excretion Ratio of (N¹-Methyl-2-pyridone-5-carboxamide + N¹-methl-4-pyridone-3-carboxamideJ/N¹-Methylnicotinamide

抄録

We have reported that the excretion ratio of nicotinamide metabolites, [N¹-methyl-2-pyridone5-carboxamide (2-Py) + N¹-methyl-4-pyridone-3-carboxamide (4-Py)]/N¹-methylnicotinamide (MNA), is used as an index of amino acid adequacy. In this experiment, effects of protein-free diet feeding or starving on this excretion ratio were investigated using rats. The experimental period was 10 days. The urinary excretion of MNA, which is a major metabolites of nicotinic acid and nicotinamide, greatly increased with days, however, the urinary excretion of the MNA metabolites, 2-Py and 4-Py, decreased when rats were fed with a protein-free diet for 10 days. Accordingly, the resulting excretion ratio of (2-Py + 4-Py)/MNA in rats fed with the protein-free diet greatly decreased compared with that in rats fed with the 20% casein diet (control) (control vs. protein-free diet groups was 21.0 ± 3.5 vs. 0.5 ± 0.1 in urine samples on day 9-10). The urinary excretion of MNA did not increase when rats were starved for 10 days compared with that of the control. However, (2-Py + 4-Py)/MNA decreased to 3.6 ± 0.5 in urine samples on day 9-10. This decrease in the excretion ratio was attributed to the decrease in the activity of 2-Py- and 4-Py-forming MNA oxidase. These results further strengthen our claim that (2-Py + 4-Py)/MNA can be used as an index of amino acid adequacy.