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1 Departments of Surgery and Physiology, University of California Medical Center, Los Angeles, California 90024; and 2 Department of Surgery, Brigham and Women's Hospital, Boston, Massachusetts 02115
Traditionally, intestinal glucose absorption was
thought to occur through active, carrier-mediated transport. However,
proponents of paracellular transport have argued that previous
experiments neglected effects of solvent drag coming from high local
concentrations of glucose at the brush-border membrane. The purpose of
this study was to evaluate glucose absorption in the awake dog under
conditions that would maximize any contribution of paracellular
transport. Jejunal Thiry-Vella loops were constructed in six female
mongrel dogs. After surgical recovery, isotonic buffers containing
L-glucose as the probe for
paracellular permeability were given over 2-h periods by constant
infusion pump. At physiological concentrations of
D-glucose (1-50 mM), the
fractional absorption of
L-glucose was only 4-7% of
total glucose absorption. Infusion of supraphysiological concentrations
(150 mM) of D-glucose,
D-maltose, or
D-mannitol yielded
low-fractional absorptions of
L-glucose (2-5%), so too did complex or nonabsorbable carbohydrates. In all experiments, there
was significant fractional water absorption (5-19%), a
prerequisite for solvent drag. Therefore, with even up to high
concentrations of luminal carbohydrates in the presence of significant
water absorption, the relative contribution of paracellular glucose absorption remained low.
cell membrane permeability; small intestine; perfusion; mannitol; maltose; water absorption
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