The Influence of Tryptophan upon Urinary Nitrogen and Amino Acid Excretion in the Rat

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Abstract
Protein-depleted, adult rats were fed low protein diets containing tryptophan-free acid hydrolyzed casein supplemented with the other essential amino acids to render the diet adequate for maintenance. The feeding of supplementary levels of tryptophan, ranging from zero to 300 mg per 100 gm of ration, caused a marked decrease in urinary nitrogen excretion up to a point between the 50 mg and 100 mg levels. Amounts of tryptophan ranging from 100 mg to 300 mg (8 to 24 mg per rat per day) did not appreciably alter the level of excretion of urinary nitrogen. The requirement for tryptophan of adult rats fed a low protein diet supplying a minimum of the essential amino acids for maintenance and some of the non-essential amino acids, varied from 4.0 mg to 6.4 mg per 200 gm rat per day, depending upon the length of time that elapsed after feeding the protein depletion diet. The feeding of minimum levels and twice the minimum levels of the amino acids required for maintenance, in the presence of graded levels of tryptophan, resulted in a similar pattern of nitrogen excretion. When the daily food consumption was approximately 8.0 gm per day, positive nitrogen balance was possible in adult rats which received a diet containing only 2.9% protein. Excessive amounts of tryptophan in the diet caused little change in the urinary excretion of tryptophan, threonine, leucine, histidine, methionine, arginine and proline.