Adaptation of intestinal sugar and amino acid transport to gastric hyperalimentation

These studies were undertaken to analyze the effects in dogs of the administration of liquid polymeric diets by gastric tube for 14 days on brush-border absorptive functions measured in vitro. Transport studies of D-glucose, L-leucine and L-alanine have been performed by a rapid filtration technique using brush border membrane vesicles isolated from different segments of the small intestine in order to get insights about events occurring directly at the membrane level. Our results clearly show that only the Na+ -gradient dependent pathways for sugars and neutral amino acids transport were modified in treated dogs as compared to chow-fed controls. The adaptation to the diets varied according to the intestinal segment considered and the effects were dependent on both the nature of the diet and the transport function analysed. These effects cannot be due to heterogeneity in the populations of vesicles isolated in the different situations and cannot be attributed to a modification of either the passive permeability of the membrane to solutes or ions or the membrane potential. Our results are best explained by changes in carrier densities along the small intestine in response to modification in the local concentrations of nutrients sequential to faster flow rates in the small intestine. The liquid nature of the polymeric diets, combined with their high fat and low residue content as compared to dog chow, could act in concert to promote faster rates of gastric emptying and intestinal transit, thus leading to modifications in nutrient availability along the small intestine.