Abstract
The authors investigated the effect of Trp level with or without niacin (NiA) in a diet on growth of young rats and amounts of excretion into urine and contents of liver of Trp metabolites (quinolinic acid, NiA, N^1-methylnicotinamide and NAD) . The additional effect of NiA (0.003%) was observed only at Trp level 0.043% but not at 0.085, 0.17, 0.25 and 0.34% in the diets, from the result of gain in body weight and protein efficiency ratio. However, from the results of excretion and amounts of liver of Trp metabolites, the additional effect of NiA was observed not only at Trp level 0.043% but also at 0.085%. Therefore we presume that 0.085% of Trp in diet may be the point whether the additional effect of NiA is observed in young rats or not. Since Trp metabolites in liver increased depending on Trp content in the diet at the first-order reaction, the biosynthetic ability of NAD by rat liver from Trp would be fairly active. If Trp intake is higher than from that of the body protein requirement, NAD needed to all other tissues of rat would be furnished by the liver from excess amounts of Trp.
