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Xylose transport in the human jejunum
1Department of Gastroenterology, Christian Medical College Hospital, Vellore, India.
Digestive Diseases and Sciences
|April 1, 1989
Summary
D-Xylose absorption in the jejunum primarily occurs via passive diffusion, not glucose cotransport. This finding clarifies the mechanism behind the D-xylose tolerance test.
Area of Science:
- Gastroenterology
- Human Physiology
- Nutrient Absorption
Background:
- The D-xylose tolerance test is a common diagnostic tool.
- Understanding D-xylose absorption mechanisms is crucial for interpreting test results.
- Previous studies suggested potential cotransport with glucose.
Purpose of the Study:
- To investigate the transport mechanism of D-xylose in the human jejunum.
- To determine if D-xylose and D-glucose share a cotransport system.
- To clarify the physiological basis of the D-xylose tolerance test.
Main Methods:
- In vivo intestinal perfusion technique in humans.
- In vitro studies using human jejunal brush border membrane vesicles.
- Analysis of D-xylose absorption rates with varying D-glucose concentrations.
Main Results:
- D-xylose absorption rates showed a linear relationship with initial concentrations, indicating passive diffusion.
- Adding glucose to the perfusate did not significantly alter D-xylose absorption rates.
- Xylose uptake in membrane vesicles was partially inhibited by D-glucose and phlorizin.
- A minor D-glucose cotransport component was observed but overridden by passive diffusion.
Conclusions:
- Jejunal D-xylose absorption at clinical concentrations is predominantly by passive diffusion.
- The D-xylose tolerance test primarily reflects jejunal surface area and permeability.
- The test does not accurately measure nutrient carbohydrate absorption capacity.