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Nitrogen Balance of Adult Rats Fed Diets Low in L-, DL- and D-Phenylalanine¹

One Figure

Department of Physiology and Vital Economics, School of Medicine and Dentistry, University of Rochester, Rochester, New York

Nitrogen balance was determined on two groups of adult male albino rats which derived all of their dietary nitrogen from mixtures of amino acids. Each experiment included the following dietary regimes 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 quantity of diet each day.

If the phenylalanine in a complete mixture of essential amino acids is reduced sufficiently, the nitrogen balance is adversely affected. When this amino acid is the limiting factor in the utilization of dietary nitrogen, it is assumed that N balance is a linear function of phenylalanine intake. On this assumption, the requirement for maintenance of N equilibrium is 17.5 mg of L- or DL- and 19.2 mg of D-phenylalanine/day/kg^3/4.

Other values for the adult male rat and for the adult human male, computed from the data of Benditt et al. ('50) and Rose ('49), are 29.1 mg/day/kg^3/4 and 45.5 mg/day/kg^3/4 for DL- and L-phenylalanine, respectively.

Manuscript received 28 March 1952.