Nitrogen Balance of Adult Rats Fed Amino Acid Diets Low in L-, DL- and D-Tryptophan

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Abstract
Nitrogen balance was determined on a group of adult male albino rats which derived all of their dietary nitrogen from mixtures of amino acids. Each experiment included the following dietary regimens in the order given: 14 days on maintenance diet (9.6% whole egg protein); 7 days on N-free diet; 7 days on amino acid diet supplying approximately half of the maintenance requirement of total nitrogen; 7 days on double the quantity of the amino acid mixture fed in the previous period. These diets, except the maintenance diet, were fed by stomach tube in two equal portions daily, and each rat received the same amount of diet each day. If the quantity of tryptophan in the amino acid mixture is reduced sufficiently, the N balance is adversely affected. When tryptophan is the limiting factor in the utilization of total dietary N, it is assumed that N balance is a linear function of tryptophan intake. On this assumption, the requirement for maintenance of N equilibrium is 4.4 ± 0.22 mg of L-, 6.0 ± 0.31 mg of DL-, and 8.8 ± 0.57 mg of D-tryptophan/day/kg3/4.