A concentrated mixture of amino acids and dipeptides for total parenteral nutrition

Using a subhuman primate (baboon) we have investigated the utility of a 20% mixture of amino acids and dipeptides as the nitrogen source for total parental nutrition. The mixture, besides containing all 8 essential amino acids and a number of non-essential amino acids (glutamate, aspartate, arginine, histidine, serine, ornithine and alanine), contained 6 dipeptides (Gly-Ile, Gly-Leu, Gly-Val, Gly-Tyr, Gly-Gln, and Ala-Gln) and acetyl-cysteine. A week of total parenteral nutrition was preceded by one week of oral feeding. The caloric intake and composition during the two periods was identical except for the nitrogen source, which was intact protein during the oral period, and the mixture of amino acids and dipeptides during the parenteral period. There was no significant difference between gain in body weight or nitrogen balance during the two periods. There were selective increases in plasma and muscle concentrations of amino acids during the parenteral period, which appeared to reflect the amino acid enrichment of the nitrogen source. The efficient utilization of dipeptides was evidenced by their small concentrations in plasma and urine. The urinary excretion of dipeptides was about 1% of the amount infused. This efficiency of dipeptide utilization persisted even when the infusion rate of the amino acid and dipeptide mixture was increased by 7-fold. There was no alteration in liver, kidney, and immune function during the parenteral period. The data indicate the efficacy and safety of the mixture of amino acids and dipeptides as the nitrogen source for parenteral nutrition.