Stimulation of neutral amino acid transport by fructose in epithelial cells isolated from rat intestine.
Interest in the nutritional and physiological implications of the high dietary intakes of fructose from sucrose and isomerized corn sweeteners has directed attention to the specific metabolic properties of this monosaccharide. Epithelial cells isolated from the small intestine of Wistar rats fed a stock diet showed 24% to 57% higher transport of 1 mM leucine, isoleucine, valine, alanine, phenylalanine tryptophan and histidine in the presence of 10 mM fructose than in its absence. In contrast, 10mM glucose generally inhibited the transport of these amino acids and 10mM sorbose had no effect on leucine transport. Fructose failed to consistently stimulate the transport of basic amino acids and generally inhibited the transport of glucose and galactose, indicating that the stimulation was relatively specific for neutral amino acids. Cells preloaded with fructose optimally stimulated leucine transport in the absence of extracellular fructose. Ouabain and dinitrophenol inhibited the stimulation of leucine transport by intracellular fructose after 2 minutes. A stimulation mediated by an exchange transport mechanism was rejected on the basis of the failure of 1 mM neutral amino acids either to inhibit the transport of 10 mM fructose or to accelerate the movement of fructose out of fructose-loaded cells. Although the mechanism remains unknown, these results demonstrate a specific effect of fructose at the intestinal level that produces a stimulation of neutral amino acid transport.