Influence of luminal Na+ on the intestinal absorption of sugars in vivo.

The effect of substituting Na+ with Tris, Li+, K+ or mannitol on the intestinal absorption of sugars, in successive periods of 1 minute duration, has been studied in rat and hamster in vivo. The absorption of 2 mM D-glucose, D-galactose, 3-0-methyl-D-glucose and D-fructose is clearly inhibited in the absence of Na+, up to 70-80%, and returns to its normal value of restoring Na+. The degree of inhibition varies with the sugar, increases on lowering Na+ concentration, reaches maximum values with mannitol as substituent, and minimum with Tris, D-arabinose absorption is not affected by Na+. These results prove once more how important Na+ is in sugar intestinal transport in vivo, while they reveal additional influences of the different substituents on the transport system.