Effect of phloretin and phloridzin on properties of digestion and absorption in the rat small intestine

Experiments in vitro on everted sacs of rat small intestine have shown that phloretin (an inhibitor of basolatheral glucose GLUT2 transporter) added from mucosal side of the sacs decreases release of glucose from enterocytes into serosal fluid without changing glucose accumulation in tissue of the preparations. Addition of phloridzin (an inhibitor of Na+ and glucose co-transporter SGLT1) from mucosal side inhibited both glucose accumulation in the tissue and its release into serosal fluid. Unspecific effects of phloretin and phloridzin on activities of several digestive enzymes (in particular, alkaline phosphatase, amino peptidase, and glycyl-L-leucine dipeptidase) has been revealed in homogenates of the rat small intestine mucosa. In chronic experiments on rats, absorption of glycine from the isolated small intestinal loop was inhibited in the presence of phloretin in perfusate. The obtained results indicate that the experimental approach of inhibition of glucose absorption by phloretin used from mucosal side in vitro appears to give a significant overestimation of contribution of facilitated diffusion (with participation of the GLUT2 transporter inserted in the apical enterocyte membrane) to glucose transport across this membrane. Thus, the role of the GLUT2 transporter in the mechanism of glucose absorption in the small intestine under its physiological conditions does not seem to be as great as it is thought by the authors of the recently proposed hypothesis.