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J S Fordtran

Publications and source records attributed to J S Fordtran.

160 records · Page 9Linked to original sources
PubMed1968

The mechanisms of sodium absorption in the human small intestine.

The present studies were designed to characterize sodium transport in the jejunum and ileum of humans with respect to the effects of water flow, sodium concentration, addition of glucose and galactose, and variations in aniomic composition of luminal fluid. In the ileum, sodium absorption occurred against very steep electrochemical gradients (110 mEq/liter, 5-15 mv), was unaffected by the rate or direction of water flow, and was not stimulated by addition of glucose, galactose, or bicarbonate. These findings led to the conclusion that there is an efficiently active sodium transport across a membrane that is relatively impermeable to sodium. In contrast, jejunal sodium (chloride) absorption can take place against only the modest concentration gradient of 13 mEq/liter, was dramatically influenced by water movement, and was stimulated by addition of glucose, galactose, and bicarbonate. The stimulatory effect of glucose and galactose was evident even when net water movement was inhibited to zero by mannitol. These observations led to the conclusion that a small fraction of jejunal sodium absorption was mediated by active transport coupled either to active absorption of bicarbonate or active secretion of hydrogen ions. The major part of sodium absorption, i.e. sodium chloride absorption, appeared to be mediated by a process of bulk flow of solution along osmotic pressure gradients. The stimulatory effect of glucose and galactose, even at zero water flow, was explained by a model in which the active transport of monosaccharide generates a local osmotic force for the absorption of solution (NaCl and water) from the jejunal lumen, which, in the presence of mannitol, is counterbalanced by a reverse flow of pure solvent (H(2)O) through a parallel set of channels which are impermeable to sodium. Support for the model was obtained by the demonstration that glucose and bicarbonate stimulated the absorption of the nonactively transported solute urea even when net water flow was maintained at zero by addition of mannitol to luminal contents.

Adult↗
PubMed1968

Bile salt and micellar fat concentration in proximal small bowel contents of ileectomy patients.

Studies were carried out to test the hypothesis that abnormal bile salt metabolism (interruption of the enterohepatic circulation) is responsible for steatorrhea in patients with ileal disease and (or) ileectomy.Duodenal bile salt concentration after a single, standard meal eaten at 8 a.m. was measured in 8 patients with ileectomy steatorrhea and compared with 11 normal control subjects and 7 hospitalized patients without gastrointestinal disease. Mean bile salt concentration was approximately half normal in the ileectomy group, but some of the patients fell well within the normal range, even on repeat studies. However, it was shown that the second and third meals eaten during a single day were associated with a marked depression of duodenal bile salt concentration in ileectomy patients, which suggested that the first meals in these patients flush out a large fraction of the bile salt pool. Simultaneously measured turnover studies with taurocholate-(14)C showed at t((1/2)) of 3.1 hr in these patients compared with 29.5 and 32 hr in two control subjects, proving that the enterohepatic circulation had indeed been interrupted by ileectomy. Hepatic synthesis can apparently partially reconstitute the bile salt pool during the overnight period. Additional studies were carried out to determine the relation between bile salt and micellar fat concentration in proximal small bowel contents after ingestion of the same standard meal. Below a bile salt concentration of 1.7 mg/ml, less than 0.8 mg/ml of lipid existed in the micellar phase of intestinal contents, whereas when bile salt concentration exceeded this level the amount of fat in the micellar phase rose progressively. Only 1 of 11 samples from three ileectomy patients had a micellar fat concentration > 0.8 mg/ml, whereas 33 of 42 samples from control subjects had micellar fat concentration > 0.8 mg/ml.Thus, abnormally low duodenal bile salt concentration during at least a portion of the day, with the associated depression of micellar fat, appears to be a major cause of decreased fat absorption in patients with ileectomy steatorrhea.

Adult↗
PubMed1967

Water and solute movement in the small intestine of patients with sprue.

Water and electrolyte movement in the jejunum of normal subjects and patients with sprue was measured during perfusion with isotonic electrolyte solutions. Normal subjects absorbed water, sodium, and potassium. By contrast, in patients with sprue (seven with adult celiac sprue and one with tropical sprue) who had diarrhea and steatorrhea, these substances were secreted into the intestinal lumen. This indicates that the jejunal mucosa of these patients was in a secretory state with respect to water and electrolytes.A method is presented for detecting abnormalities in the effective pore size in disease states. The method is based on the principle of restrictive diffusion and involves measuring the simultaneous diffusion rates of solutes of different molecular size. Since the method does not depend on measurement of water flow in response to osmotic pressure gradients, it can be used in disease states in which absorption and secretory processes involving water may be abnormal.The ratio of urea to tritiated water diffusion in the jejunum of normal subjects averaged 0.8, compared to 0.2 in patients with sprue. This indicates a marked decrease in the effective pore size of the jejunal mucosa in sprue. This conclusion was strengthened by the finding that erythritol and L-xylose, which are somewhat larger solutes than urea, are essentially non-absorbable in small bowel involved with sprue.

Adult↗