Absorption of sugars from isolated surviving intestine

Abstract

1. 1. The rate of fructose absorption from the isolated surviving intestine, when the lumen of this is perfused with a fructose solution, increases with increase of concentration of fructose. A limiting value for fructose absorption, however, is reached. This phenomenon of a limiting rate of sugar absorption is shown not only by fructose but by sorbose and sucrose. 2. 2. The rate of glucose appearance on the serosal aspect of the intestine exceeds that of fructose, at low concentrations of fructose in the mucosal solution, and is less than that of fructose at high concentrations of fructose in the mucosal solution. 3. 3. The presence of anaerobic conditions, or that of 2,4-dinitrophenol under aerobic conditions, suppresses glucose formation from fructose in the isolated intestine but has no influence on the rate of absorption of fructose. 4. 4. The presence of phlorizin suppresses “active” glucose absorption from the intestine but, at the concentrations investigated, has no effect on the rate of fructose absorption or on glucose formation from fructose. The results conform with the conclusion that there is no “active” absorption of fructose and that glucose formation from fructose in the intestine is enzymically controlled. 5. 5. Sucrose is absorbed “passively” by the isolated intestine, its rate of absorption being unaffected by anaerobic conditions. The presence of phlorizin has no effect on the rate of absorption of sucrose, but it suppresses the rate of glucose appearance. 6. 6. Substitution of sucrose by an equimolar concentration of invert sugar has no significant effect on the rates at which glucose and fructose appear on the serosal side of the intestine, whether the conditions are aerobic or anaerobic. It is concluded that hydrolysis of the sucrose occurs after its entry into the intestinal tissue.