Effect of luminal Na+ on the kinetics of intestinal absorption of sugars in vivo

Abstract

The effect of sodium concentration on the absorption kinetics of glucose, galactose and 3-o-methyl-glucose in rat and hamster jejunum in vivo has been studied.In consecutive 1 min periods the total absorption and absorption in presence of 0.5 mM phlorizin were measured.The difference between them was taken as the active transport rate.The perfusion rate value was 5.6 ml X min-1 and sugar concentrations in the perfusion solution ranged from 1 to 10 mM.The results for the different sodium concentrations show a nearly common Vmax for the same sugar and animal species, while the apparent KT values increase when the sodium concentration in the lumen decreases, mimicking a pure affinity-type activation system.The absorption of sugar when solutions without Na+ are perfused, is greater than that entering passively in the presence of phlorizin.An explanation may be that appreciable amounts of endogenous Na+ find their way to the intestinal lumen in favour of the gradient, making Na+-sugar cotransport possible.