Luminal glucose concentrations in the gut under normal conditions

R. P. Ferraris, S. Yasharpour, K. C.K. Lloyd, R. Mirzayan, J. M. Diamond

Research output: Contribution to journalArticle

206 Citations (Scopus)

Abstract

Luminal glucose (Glc) concentrations in the small intestine (SI) are widely assumed to be 50-500 mM. These values have posed problems for interpreting SI luminal osmolality and absorptive capacity, Glc transporter Michaelis-Menten constants (K(m)), and the physiological role of active Glc transport and its regulation. Hence we measured luminal contents, osmolality, and Glc, Na+, and K+ concentrations in normally feeding rats, rabbits, and dogs. Measured Glc concentrations were compatible with the portion of measured osmolality not accounted for by Na+ and K+ salts, amino acids, and peptides. Mean SI luminal osmolalities were ≤100 mosmol/kg hypertonic. For animals on the most nearly physiological diets, SI Glc concentrations averaged 0.4-24 mM and ranged with time and SI region from 0.2 to a maximum of 48 mM. The older published very high values are artifacts of direct infusion of concentrated Glc solutions into the gut, nonspecific Glc assays, and failure to test for quantitative recovery or to centrifuge samples in the cold. By storing food after meals and releasing it between meals, rat stomach greatly damps diurnal fluctuations in quantity and osmolality of food reaching the SI and hence also damps fluctuations in absorption rates. These new values for luminal Glc have five important physiological implications: the problem of accounting for apparently very hypertonic SI contents in the face of high osmotic water permeability disappears; the effective K(m) of the SI Glc transporter is now comparable to prevailing Glc concentrations; the SI no longer appears to have enormous excess absorptive capacity for Glc; regulation of Glc transport by dietary intake now makes functional sense; and the claim that high luminal Glc concentrations permit solvent drag to become the major mode of Glc absorption under normal conditions is undermined.

Original languageEnglish (US)
Pages (from-to)G822-G837
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume259
Issue number5 22-5
StatePublished - Jan 1 1990

Fingerprint

Glucose
Small Intestine
Osmolar Concentration
Facilitative Glucose Transport Proteins
Meals
Food
Active Biological Transport
Artifacts
Permeability
Stomach
Salts
Dogs
Diet
Rabbits
Amino Acids
Peptides
Water

All Science Journal Classification (ASJC) codes

  • Physiology
  • Hepatology
  • Gastroenterology
  • Physiology (medical)

Keywords

  • Glucose absorption
  • Glucose transporter
  • Michaelis-Menten constant
  • Osmolality
  • Small intestine
  • Stomach

Cite this

Ferraris, R. P., Yasharpour, S., Lloyd, K. C. K., Mirzayan, R., & Diamond, J. M. (1990). Luminal glucose concentrations in the gut under normal conditions. American Journal of Physiology - Gastrointestinal and Liver Physiology, 259(5 22-5), G822-G837.
Ferraris, R. P. ; Yasharpour, S. ; Lloyd, K. C.K. ; Mirzayan, R. ; Diamond, J. M. / Luminal glucose concentrations in the gut under normal conditions. In: American Journal of Physiology - Gastrointestinal and Liver Physiology. 1990 ; Vol. 259, No. 5 22-5. pp. G822-G837.
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Ferraris, RP, Yasharpour, S, Lloyd, KCK, Mirzayan, R & Diamond, JM 1990, 'Luminal glucose concentrations in the gut under normal conditions', American Journal of Physiology - Gastrointestinal and Liver Physiology, vol. 259, no. 5 22-5, pp. G822-G837.

Luminal glucose concentrations in the gut under normal conditions. / Ferraris, R. P.; Yasharpour, S.; Lloyd, K. C.K.; Mirzayan, R.; Diamond, J. M.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 259, No. 5 22-5, 01.01.1990, p. G822-G837.

Research output: Contribution to journalArticle

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AU - Ferraris, R. P.

AU - Yasharpour, S.

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AB - Luminal glucose (Glc) concentrations in the small intestine (SI) are widely assumed to be 50-500 mM. These values have posed problems for interpreting SI luminal osmolality and absorptive capacity, Glc transporter Michaelis-Menten constants (K(m)), and the physiological role of active Glc transport and its regulation. Hence we measured luminal contents, osmolality, and Glc, Na+, and K+ concentrations in normally feeding rats, rabbits, and dogs. Measured Glc concentrations were compatible with the portion of measured osmolality not accounted for by Na+ and K+ salts, amino acids, and peptides. Mean SI luminal osmolalities were ≤100 mosmol/kg hypertonic. For animals on the most nearly physiological diets, SI Glc concentrations averaged 0.4-24 mM and ranged with time and SI region from 0.2 to a maximum of 48 mM. The older published very high values are artifacts of direct infusion of concentrated Glc solutions into the gut, nonspecific Glc assays, and failure to test for quantitative recovery or to centrifuge samples in the cold. By storing food after meals and releasing it between meals, rat stomach greatly damps diurnal fluctuations in quantity and osmolality of food reaching the SI and hence also damps fluctuations in absorption rates. These new values for luminal Glc have five important physiological implications: the problem of accounting for apparently very hypertonic SI contents in the face of high osmotic water permeability disappears; the effective K(m) of the SI Glc transporter is now comparable to prevailing Glc concentrations; the SI no longer appears to have enormous excess absorptive capacity for Glc; regulation of Glc transport by dietary intake now makes functional sense; and the claim that high luminal Glc concentrations permit solvent drag to become the major mode of Glc absorption under normal conditions is undermined.

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KW - Stomach

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