Efficacy of a synthetic dipeptide mixture as the source of amino acids for total parenteral nutrition in a subhuman primate (baboon). Plasma concentration, metabolic clearance, and urinary excretion of a series of dipeptides.

To assess the efficacy and safety of oligopeptides as substrates for total parenteral nutrition, we investigated the effects of intravenous infusion of a synthetic dipeptide mixture, as compared with a corresponding amino acid mixture, on a range of parameters of nutrition, metabolism, and organ function in baboons. In all respects the two periods of total parenteral nutrition, each lasting for 1 wk, were identical except for the difference between the forms of amino acids in the parenteral solutions, being in free form in one period and in dipeptide form in the other. The dipeptide mixture was composed of a series of 12 dipeptides each containing glycine in the N-terminal position and either an essential or nonessential amino acid in the carboxyl position. The infusion of the dipeptide mixture and the amino acid mixture had similar effects on parameters of protein nutrition (e.g., nitrogen balance, plasma aminogram, urinary excretion of 3-methylhistidine) and metabolism (such as plasma concentrations of insulin, glucose, lipids). During infusion of the dipeptide mixture, rapid metabolic clearance resulted in a barely detectable concentration of most dipeptides in plasma. Total loss of dipeptides was 1.3% +/- 0.1% of the infused amount. The functions of liver, kidney, bone marrow, and the immune system remained the same before and during the two periods of treatment. In conclusion, the data showed that (a) there was efficient utilization of dipeptides when infused as a mixture and (b) parameters of nutrition, metabolism, and organ function were well maintained after 1 wk of total parenteral nutrition with the dipeptide mixture acting as the sole nitrogen source.