Sugar transfer from the lumen of the rat small intestine to the vascular bed.

1. A modification of the vascular perfusion technique was used to investigate sugar transfer from the lumen of the rat small intestine to the vascular perfusion technique was used to investigate sugar transfer from the lumen of the rat small intestine to the vascular bed. 2. With this method the transfer of both D-[3H]galactose and L-[14C]glucose were followed in the same experiments. The results indicate that when equimolar concentrations of the two sugars are perfused through the lumen there is a preferential transfer of galactose from the mucosal epithelium to the vascular bed as well as from lumen to the epithelial layer. 3. At high rates of galactose transfer from the lumen to the vascular bed, accumulation of the sugar within the mucosal epithelium is minimal unless the vascular flow is stopped. 4. Phlorizin inhibits galactose transfer from the lumen to the vascular bed, but the inhibition of sugar transfer appears to be restricted to the luminal face of the epithelial cells since the selectivity of the basolateral exit process is unaffected. 5. Replacement of Na+ by K+ in the luminal perfusate reduces the rate of galactose transfer by a factor of 40, but does not completely abolish the preferential transfer of galactose. The presence of luminal Na+ also stimulates the exit of galactose from the mucosal epithelium to the vascular bed. 6. The presence of D-glucose in the vascular perfusate produces a two- to threefold increase in the rate of sugar transfer from the lumen to the vascular bed. This effect is not observed with vascular galactose or luminal glucose.