Protein Digestion in Human Intestine as Reflected in Luminal, Mucosal, and Plasma Amino Acid Concentrations after Meals

Abstract

A B S T R A C T Normal human volunteers were intubated with either aspiration tubes or a biopsy capsule placed in the small intestine. The subjects were then fed a test meal containing 50 g of purified bovine serum albumin which served as the model dietary protein.Electrophoretic analysis of intestinal fluids showed that for at least 4 h the fed albumin was detectable in jejunal and ileal fluids. On separate occasions, subjects were fed the same meal without the protein. No protein was detected in intestinal fluids when the protein-free meal was fed. After the protein-rich meal, total concentrations of measured free and peptide amino acids rose from 3.21 to 29.29, and 15.94 to 117.97 ,umol/ml, respectively, (P values <0.02) in the jejunum. Similarly, total concentrations of measured free and peptide amino acids rose from 5.45 to 19.74, and 13.59 to 65.39, respectively, (P values < 0.05) in the ileum. In contrast, concentrations of free and peptide amino acids in intestinal fluids did not increase after the protein-free meal. While intracellular concentrations of amino acids in the jejunal mucosa did not show significant changes, plasma concentrations of each individual free amino acid were increased after the protein-rich meal and were either decreased or unaltered after the proteinfree meal. The amino acid composition of the fed protein was reflected in the increases in intraluminal and plasma concentrations of individual amino acids after the protein-rich meal. It is concluded that after the ingestion of a test meal containing a substantial amount of protein which is within the usual range of dietary

L-Amino Acids Regulate Parathyroid Hormone Secretion

“…6C). A -fold concentration change of this magnitude approximates what is observed in response to a protein-rich meal (11,(13)(14)(15) or between the 24-h trough and peak levels of the normal circadian rhythm (16,17). In addition, the observed inhibitory effects of individual L-amino acids on PTH secretion in the presence of the 1ϫ mixture (Figs.…”

Dairy protein and leucine alter GLP-1 release and mRNA of genes involved in intestinal lipid metabolism in vitro

“…However, the objective of this study was to determine BCAA-enterocyte interactions in a direct manner, thereby reflecting luminal concentrations of amino acids. Adibi and Mercer [45] assessed the concentrations of amino acids in the intestinal lumen, mucosa, and plasma after a protein-rich meal in humans. The concentrations of total amino acids in jejunal contents 3 h after a test meal were 29.29 μmol/mL for free amino acids and 117.97 μmol/mL for peptide amino acids [45].…”

“…Adibi and Mercer [45] assessed the concentrations of amino acids in the intestinal lumen, mucosa, and plasma after a protein-rich meal in humans. The concentrations of total amino acids in jejunal contents 3 h after a test meal were 29.29 μmol/mL for free amino acids and 117.97 μmol/mL for peptide amino acids [45]. In the more distal segment of the intestine, the ileal contents contained concentrations of total amino acids after a meal that were 19.74 μmol/mL for free amino acids and 65.29 μmol/mL for peptide amino acids.…”

Protein digestion and amino acid absorption along the intestine of the common carp (Cyprinus carpio L.), a stomachless fish : an in vivo study

“…Adibi and Mercer (1973), di-, tri-and tetra-peptides constitute a major portion of the soluble nitrogenous compounds in this preparation. Chung et al (1979) confirmed that the fraction separated on Sephadex G-25 column into oligopeptides and supernatant after sulfosalicyclic acid precipitation had essentially the same -amino nitrogen concentrations.…”