Glucose accumulation by rat small intestine during absorption in vivo

GLUCOSE is transported across the mammalian small intestine even when its concentration in the lumen is lower than that in the plasma. According to the hypothesis of Crane 1 , this ‘active transport’ is coupled to the movement of sodium ions, which are maintained at a lower concentration in the mucosal epithelium of the gut than in the lumen. Glucose and sodium are thought to combine with a ‘carrier’ molecule at some external site on the brush border of the epithelial cells, the glucose then moving uphill into the cell at the expense of the movement of sodium down its electrochemical potential gradient 2 . The concentration of glucose in the mucosa rises to a level above that in the blood capillaries at the base of the epithelium, so that the sugar can move downhill into the plasma. The accumulation of glucose to give a tissue concentration higher than that in the bathing fluid has repeatedly been observed in a wide variety of in vitro intestinal preparations and is here extended to an in vivo situation.