The effect of the oral administration of leucine on the metabolism of tryptophan

Abstract

The oral administration of leucine increased the urinary excretion of quinolinic acid and decreased the excretion of tryptophan, the 6-pyridone of N-methylnicotinamide and 5-hydroxyindolylacetic acid, both in normal subjects and in patients suffering from pellagra. When a tryptophan load was given, leucine had similar effects on the urinary excretion of tryptophan, quinolinic acid and the 6-pyridone of N-methylnicotinamide. In the presence of a nicotinamide load, however, there was a much smaller decrease in the urinary excretion of the 6-pyridone of N-methylnicotinamide observed with leucine. The oral administration of lysine had no effect on the urinary excretion of nicotinic acid, quinolinic acid and the 6-pyridone of N-methylnicotinamide.