Intestinal amino acid content in critically ill patients

The purpose of the study was to determine the concentrations of free amino acids and the total protein content of the human intestinal mucosa during critical illness. The free amino acid and protein concentrations in endoscopically obtained biopsy specimens from the duodenum and the distal colonic segments were determined on 19 critically ill patients. The free amino acids were separated by ion exchange chromatography and detected by fluorescence, and the protein content was quantified by the method of Lowry. In general, the typical amino acid pattern of the intestinal mucosa was seen, with very high levels of taurine, aspartate and glutamic acid. The main difference, as compared to a reference series of healthy subjects, was the elevated glutamine concentration of the duodenal mucosa. This amino acid was unaltered in the descending colon and depressed in the rectum. At the same time, the glutamatic acid concentrations were unaltered, suggesting that the degradation of glutamine was not increased in the septic state of the majority of the patients studied. Phenylalanine and the two branched-chain amino acids, valine and leucine, were elevated in the duodenal mucosa, and in the colonic mucosa, methionine and phenylalanine were elevated; otherwise, all the other individual amino acids were unaltered or depressed. The alterations seen in mucosal free amino acid and protein concentrations in connection with critical illness are different in many respects and contrast with the findings seen after starvation or moderate surgical trauma.