Glucose uptake and regulation by intestinal tissues: Implications and whole-body energetics

Abstract

The purpose of this review is to examine mechanisms of glucose absorption by the ruminant small intestine and to relate these processes to avail- able information on the theoretical advantages of shift- ing site of starch digestion in ruminants. The primary mechanism for glucose absorption across the brush- border membrane of enterocytes is the Na + -dependent glucose transporter, SGLT1. This transport protein is a high-affinity, concentrative, glucose transporter that couples glucose transport to an inwardly directed Na + gradient. This Na + gradient is maintained by the activ- ity of Na + /K + -ATPase in the basolateral membrane. The activity of SGLT1 is highest in the developing ruminant and declines after weaning. Glucose transporter activ- ity can be increased by intraluminal glucose; however, glucose absorption or metabolism is not necessary to induce transporter activity. Changes in SGLT1 activity are proportional to SGLT1 protein content. In contrast, SGLT1 mRNA levels are poorly correlated with SGLT1 activity, suggesting post-transcriptional regulation.