NONRUMINANT NUTRITION SYMPOSIUM: Intestinal glucose sensing and regulation of glucose absorption: Implications for swine nutrition

The Na(+)/glucose cotransporter (SGLT1) is the major route for the transport of dietary sugars from the lumen of the intestine into enterocytes. Regulation of this protein is essential for the provision of glucose to the body and avoidance of intestinal malabsorption. This has important nutritional implications in particular for young and growing animals. It has been demonstrated that dietary sugars and artificial sweeteners increase SGLT1 expression and the capacity of the gut to absorb monosaccharides. Furthermore, diets supplemented with artificial sweeteners have been shown to improve growth and performance of weaning piglets. In this review, after describing the organization of intestinal epithelium, the type of gut hormones released in response to dietary carbohydrates, the mechanism underlying the transcellular transport of glucose in the intestine is outlined. Next, a historical background to the work carried out in various laboratories aimed at identifying molecular mechanisms involved in regulation of intestinal glucose transporter, SGLT1, is described. Subsequently, the more recent data on the role of intestinal glucose, or sweet, sensor T1R2 + T1R3, a G protein-coupled receptor, required for upregulation of SGLT1 by dietary sugars and artificial sweeteners, are presented. The glucose sensor subunits, T1R2 + T1R3, are members of the taste receptor family 1, T1R, and are expressed in the gut enteroendocrine cells. Sensing of dietary sugars and artificial sweeteners by T1R2 + T1R3 activates a pathway in endocrine cells leading to secretion of gut hormones. Finally, after describing molecular mechanisms by which a specific gut hormone released by endocrine cells may regulate SGLT1 expression in the neighboring absorptive enterocytes, the application of these findings to enhancing intestinal capacity to absorb dietary sugars in weaning piglets is presented. A better understanding of the molecular events involved in regulation of SGLT1 will allow the identification of nutritional targets with attendant promise of avoiding nutrient malabsorption and enhancing growth and well-being of species.