Nitrogen Balance of Adult Rats Fed Diets Low in L- and Dl-Lysine, or Devoid of Arginine

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 lysine 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 lysine intake. On this assumption the requirement for the maintenance of N equilibrium is 3.6 ± 0.07 mg of l- and 7.8 ± 0.27 mg of dl-lysine/day/kg^¾.