Nutritional value of protein hydrolysis products (oligopeptides and free amino acids) as a consequence of absorption and metabolism kinetics

When pigs were submitted to duodenal infusion of solutions containing a large percentage of small peptides (PEP) or free amino acids with the same pattern (AAL) amino acids appear in the portal blood more rapidly and more uniformly after infusion of PEP then after infusion of AAL, with the notable exception of methionine for which the opposite was true. These differences were lowered when a carbohydrate (maltose dextrin) was present in the solution, but nevertheless remained significant for the first hour after the infusion. The long-term (8-hour) uptake of free amino acids into the liver and the peripheral tissues differed in profile according to the nature of the duodenal infusion. Peripheral uptake was appreciably less well balanced after infusion of free amino acids (deficiency of threonine and phenylalanine) than after infusion of small peptides (deficiency of methionine). Accordingly, in the rat, under conditions of discontinuous enteral nutrition the mixture of small peptides was of greater nutritive value than the mixture of free amino acids. It thus appears that the absorption kinetics which results in important variations in the temporal distribution of free amino acids in the tissues may be at the origin of transitory imbalances in tissue amino acid uptake, and as a result of a lower nutritive value.