Most, if not all, ingested protein is degraded into amino acids, which are then absorbed. Absorption of amino acids has been studied in intact animals, everted gut sacs, and in other preparations of intestine. These studies have been reviewed recently (1, 2). Comparatively little is known, however, about amino acid absorption in the human. Kuroda and Gimbel (3) showed that when racemic amino acids were placed in the isolated ileal loop of a patient operated on for ulcerative colitis, the L-isomer disappeared faster than the D-isomer. Cummins (4) reported a directly proportional increase in the amount of DLmethionine that disappeared from a length of gut when the concentration of the amino acid was doubled. The kinetics of absorption of L-methionine at various sites in the human small intestine were determined by Schedl and Clifton (5). The uptake of certain amino acids by human intestinal biopsy specimens is dependent, at least in part, on active transport (6, 7). This report presents results of studies on absortion of glycine and L-alanine in human subjects. These amino acids were chosen for study because considerable information is available about their absorption by in vitro preparations. Glycine and L-alanine in man appear to be absorbed by active transport processes and to share a common absorptive pathway for which L-alanine has greater affinity. These findings agree with the results of studies in tissue preparations. MethodsStudies were performed in three normal adult male subjects. Fifty-five separate studies were carried out: 25 in the first, 21 in the second, and 9 in the third subject. Each individual was intubated with a tube assembly consisting of two polyvinyl tubes joined along their lengths by a solvent, tetrahydrofuran. One tube had an inlet (perfusion opening) that was 15 cm proximal to the distal recovery opening in the other tube. The sites of the openings were marked with mercury, and the tube position was identified at the beginning and end of each study by image intensifier fluoroscopy. The perfusion opening was positioned just distal to the duodenojejunal junction and repositioned at this site at the start of each study. Tube progression during each study was minimal, and the tip never passed farther than one jejunal loop. The subjects tolerated the tube in place for 3 to 4 days and continued to eat and to maintain normal ward activity. The tube was then removed and the cycle begun again after an interval of at least 3 days.Each study was done in the morning after an overnight fast during which water intake was permitted. The studies were performed as "steady state" experiments with the jejunal segment constantly perfused with the same solution. Perfusion was done with a peristaltic pump 1 set to deliver at a constant rate of 12 ml per minute, and the amount of fluid delivered during each period was measured. Recovery of the fluid from the opening 15 cm distal to the perfusing site was maintained by siphonage. The of PEG in the perfusate and aspirate. This calculation assumes that PEG...
The APS Journal Legacy Content is the corpus of 100 years of historical scientific research from the American Physiological Society research journals. This package goes back to the first issue of each of the APS journals including the American Journal of Physiology, first published in 1898. The full text scanned images of the printed pages are easily searchable. Downloads quickly in PDF format.
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