Comparison of oral feeding of peptide and amino acid meals to normal human subjects

Abstract

SUMMARY Intestinal perfusion studies performed in man have suggested that amino acid nitrogen may be absorbed more rapidly from peptides than free amino acids. The aim of the present study was to compare the effects of the oral administration of peptides and free amino acids. Two isonitrogenous liquid test meals, one containing 50 g of a partial enzymic hydrolysate of fish protein in which approximately 80 % of the nitrogen content was present as small peptides (peptide meal), and the other a mixture of free amino acids (amino acid meal) the composition and molar pattern of which simulated that of the peptide meal, were administered on separate occasions to six normal subjects intubated with a triple lumen tube. Both meals contained the reference marker polyethylene glycol. Fractional absorption of amino acid residues one and two hours after ingestion of the two meals was similar at three intestinal locations situated 120, 160, and 200 cm from the mouth of each subject, and at two hours 73-8 % and 72-0% of the amino acid residues had been absorbed respectively by the time the contents of the peptide and amino acid meals reached the middle sampling port of the tube. The total sum of individual amino acid increments in plasma was significantly greater 30 minutes (p < 0 025) and one hour (p < 005) after ingestion of the peptide than amino acid meals. By three hours the total area under the two plasma curves was similar. Normal human subjects thus appeared to be capable of assimilating orally administered mixtures of peptides and free amino acids with equal efficiency. Secretion of fluid into the lumen of the upper small intestine, assessed by reference to dilution of the polyethylene glycol, was less after ingestion of the peptide meal. In clinical situations characterised by fluid and electrolyte malabsorption consideration might be given to using small peptides rather than free amino acids as the nitrogen source in nutritional diets.The processes involved in the absorption of the final products of luminal proteolysis in the human small intestine are complex. Amino acids on release into free solution are absorbed by at least four group specific carrier-mediated active transport systems (Saunders and Isselbacher, 1966;Gray and Cooper, 1971). In addition to these transport systems, a separate system capable of mediating the transport of unhydrolysed dipeptides and tripeptides across the microvillous membrane into the mucosal cell has

Relation between in vitro and in vivo assessment of amino acid availability

“…As (Silk et aL, 1979;Adibi and Kim, 1981), this seemed from the present results as from previous ones (Galibois and Savoie, 1987) (Christensen, 1982;McNurlan and Garlick, 1984). For instance, a large part of histidine released in portal blood may come from the hydrolysis of endogenous blood dipeptides such as carnosine, that would take place in the intestinal tissue (Rérat et al, 1988 (Laplace, 1979), and the important role that peptidases from the intestinal brush-border and from enterocytes play in the digestion of proteins (Silk et aL, 1985).…”

Characterization and Nutritional Significance of Peptide Transport in Man

“…There were no signif icant differences at later times, and the area under the two plasma a-NH2 nitrogen vs. time curves was the same. Both the fish pro tein test meals contained PEG (4 g/1) made it possible to obtain an estimate of fractional absorption values of the amino acid residues from the two meals [44], Approximately 85% of the amino acid content of both meals had been absorbed by the time the meal contents had reached the middle sampling port situ ated 60 cm from the mouth. In contrast to the perfusion studies, however [18], there was no significant difference in the fractional absorption rates of any of the individual amino acid residues from the two meals at any of the three intestinal locations at any time period (0.5-4 h) after meal ingestion.…”

“…In order to determine if the observed differences could be extrapolated to the normal physio logical and therefore clinical setting, test meal studies were performed in which the fish pro tein and lactalbumin hydrolysates, together with their respective equivalent free amino acid mixtures were fed orally to normal sub jects [25,44], Following oral ingestion of isonitrogenous amounts of fish protein hydrolysate (50 g) and its equivalent free amino acid mixture (54.4 g), plasma increments of CI-NH2 nitro gen were significantly greater 30 min and 1 h after ingestion of the peptide than amino acid meal (p < 0.05; fig. 6).…”

Amino acid and peptide absorption after proximal small intestinal resection in the rat.

“…Aliquots of samples from both the perfused dipeptide and the free amino acid mixture along with a standard 1 mM L-leucine solution were then appropriately diluted, prepared in dupli-cate, and incubated in a shaking water bath at 37°C for 20 minutes with L-amino acid oxidase reagent (Heizer et al, 1972;Nicholson and Kim, 1975 (Silk et al, 1974a;1976b). Quench correction was made by external standardisation.…”

“…Treatment in this situation may include oral administration of free amino acid mixtures as elemental diets (Thompson et al, 1969). Alternatively, small peptides, rather than more costly and more hyperosmotic free amino acid mixtures (Silk et al, 1976a;Silk, 1977), might also be administered in the short bowel syndrome.…”