Inhibition of intestinal amino acid transport by hexoses.

Abstract

Abstract 1. 1. Studies are presented which indicate that the intestinal transport of some amino acids may be inhibited in vitro by the presence of galactose or fructose in the medium. Intestinal slices from rats fed 30% galactose or fructose show a defect in the intestinal transport of certain amino acids. Fructose-fed, like galactose-fed rats, develop an aminoaciduria. 2. 2. In the presence of galactose, inhibition of the transport of neutral amino acids (alanine, valine, glycine) and hydroxyproline was noted. Studies on slices from galactose-fed rats were similar except that hydroxyproline transport was not impaired. In the presence of fructose, alanine and glycine transport was inhibited, but in the slices from fructose-fed animals only alanine transport was depressed. Kinetic studies revealed that the inhibition of alanine transport by galactose was non-competitive. A defect in the transport of basic amino acids or phenylalanine could not be demonstrated. 3. 3. ATP levels were measured in intestinal slices incubated in the presence of sugars and in the intestinal slices from rats fed galactose or fructose. No direct quantitative relationship was found between changes in intestinal ATP levels and alterations in amino acid transport. 4. 4. Galactose 1-phosphate accumulated in intestinal slices incubated in the presence of galactose and was also present in the intestine of galactose-fed rats. The possible role of the accumulation of this metabolite in the inhibition of amino acid transport by galactose remains to be determined. 5. 5. It is suggested that in galactosemia and hereditary fructose intolerance a similar defect in the intestinal transport of certain amino acids may also occur.