Effect of region of intestine and unstirred layers on uptake of sugars into rabbit intestine.

The kinetic characteristics of the transport of four sugars were determined in rabbit jejunum and ileum. The effective resistance of the intestinal unstirred layer and the rates of uptake of glucose, galactose, 3-O-methyl glucose and fructose were assessed in vitro. The unstirred layer resistance was higher in jejunum than in ileum at all rates of stirring of the bulk phase. The maximal transport rates, Jmd, of galactose and 3-O-methyl glucose were higher than the Jmd of glucose, which in turn was higher than that for fructose. The Jmd of glucose, galactose, and fructose were each lower in ileum than in jejunum, but the Jmd of 3-O-methyl glucose in the ileum was similar to both regions. For the single Michaelis-Menten model, the values of the Michaelis constant, Km, for glucose and galactose were slightly lower in the jejunum than in the ileum, whereas the value of the Km for 3-O-methyl glucose and for fructose were similar in the two sites. In the jejunum, the relative values of the Km were 3-O-methyl glucose = fructose greater than galactose greater than glucose. It is regarded that variations in sugar absorption between the jejunum and ileum are due to differences in the values of the effective resistance of the unstirred water layer, the maximal transport rate, and the Michaelis constant.