Effect of Threonine-induced Amino Acid Imbalance on the Excretion of Tryptophan Metabolites by the Rat

Amino acid imbalance was produced in rats fed a 9% salt-free acid hydrolyzed casein niacin-free diet with 0.09% of DL-tryptophan and 0.40% of DL-threonine. By inclusion of radiotryptophan in the diet toward the end of the experiment, the extent of excretion of tryptophan and its metabolities through carbon dioxide, urine and feces was estimated. It was shown that the experimental rats excreted a greater percentage of the administered radiotryptophan through carbon dioxide, urine and feces than their controls. These results support the hypothesis that in amino acid imbalance, concomitant with the excretion of the surplus amino acids, there is a wasting of the limiting amino acid through catabolism and excretion, thus increasing the deficiency and retarding growth.