Paracellular glucose transport plays a minor role in the unanesthetized dog

Traditionally, intestinal glucose absorption was thought to occur through a ctive, carrier-mediated transport. However, proponents of paracellular tran sport have argued that previous experiments neglected effects of solvent dr ag coming from high local concentrations of glucose at the brush-border mem brane. The purpose of this study was to evaluate glucose absorption in the awake dog under conditions that would maximize any contribution of paracell ular transport. Jejunal Thiry-Vella loops were constructed in six female mo ngrel dogs. After surgical recovery, isotonic buffers containing L-glucose as the probe for paracellular permeability were given over 2-h periods by c onstant infusion pump. At physiological concentrations of D-glucose (1-50 m M), the fractional absorption of L-glucose was only 4-7% of total glucose a bsorption. Infusion of supraphysiological concentrations (150 mM) of D-gluc ose, D-maltose, or D-mannitol yielded low-fractional absorptions of L-gluco se (2-5%), so too did complex or nonabsorbable carbohydrates. In all experi ments, there was significant fractional water absorption (5-19%), a prerequ isite for solvent drag. Therefore, with even up to high concentrations of l uminal carbohydrates in the presence of significant water absorption, the r elative contribution of paracellular glucose absorption remained low.