Amino Acid Homeostasis in the Small Intestine. I. Studies in the Rat

Abstract

To test the hypothesis that efflux of amino acids into the small intestinal lumen can occur during absorption, amino acid solutions at various concentrations have been instilled into the intestine of the rat and left there for periods of one hour. These experiments indicate that an efficient homeostatic mechanism for free amino acids is present in the small intestine of the rat.

Amino Acid Homeostasis in the Small Intestine. II. Studies in Man

“…These values were compared with the concentrations in the aspirated fluid of those amino acids which were absent from the initial perfusion fluid. These values are given in The results from all 15 perfusion studies show a good deal of variation, but this was to be expected as only 30 cm of the jejunum was perfused, in contrast with the experiments with rats [6] in which the whole of the small intestine was studied. However, certain conclusions can be drawn and these are shown in figures 1-4, which represent the free amino acid concentrations in the perfused fluid and in the aspirates for one subject with a normal jejunum, the coeliac syndrome, chronic pancreatitis, and a deficiency of Paneth cells, respectively.…”

“…The rat experiments which we have carried out [6] show that even with the pancreatic and biliary secretions excluded, amino acid homeostasis will still occur. Only one patient with a deficiency of Paneth cells was studied.…”

“…It has been demonstrated that an efficient homeostatic mechanism for amino acids is present in the small intestine of man and the rat [6], In the upper small intestine homeostasis seems to be brought about by the entry of pancreatic and biliary secretions into the lumen, the pancreatic contri bution being by far the most important. Also, throughout the length of the small intestine, a steady contribution is made by cells exfoliated from the intestinal mucosa, but in view of the large amounts of endogenous amino acid entering the lumen [20], such cell loss probably plays a small part in homeostasis.…”

“…Several studies have shown clearly that endogenous protein and free amino acids enter the small intestine during the process of digestion [10,20,24], It has been demonstrated that the quantity of this movement may be considerable. Most of these studies, however, have been carried out on animals [6], and the process in man has been studied only in healthy subjects. The purpose of the present work was to study firstly small intestinal amino acid homeostasis in both healthy and ill subjects, and secondly to determine, if possible, the origin of the free amino acids which enter the small intestine in man.…”