Direct and indirect effects of dextrose and amino acids on gut mass.

Oral intake of an elemental diet maintains small intestinal mucosal mass compared to the atrophy seen after intravenous infusion of the same diet. The greatest difference in intestinal mass occurs in the proximal bowel and is thought to occur because of rapid absorption in the proximal small bowel. This study was designed to determine the effects of the individual components of the elemental diet and their site of administration within the small bowel on small intestinal mass. Rats were maintained on intravenous alimentation and the proximal gut (by intragastric infusion) or the ileum was continuously infused with equal volumes of 30% dextrose, 5% dextrose, 5% amino acids, saline, or 30% mannitol. After 1 week of combined intravenous alimentation and gut infusion, the rats were killed and parameters of small intestinal epithelial mass were determined sequentially for the entire bowel. Although saline- and mannitol-infused controls did not differ from uninfused intravenously fed rats, proximal infusion of 30% dextrose reproduced the effects of a complete elemental diet. Proximal infusion of amino acids but not 5% dextrose had a limited effect on the duodenum and jejunum. Ileal infusion of 30% dextrose led to local hyperplasia of the site of infusion and in addition produced hyperplasia of the proximal gut. Ileal amino acid infusion, but not 5% dextrose infusion, led to local ileal hyperplasia. We conclude that: (1) intraluminal dextrose and amino acids have direct effects in maintaining gut mass (2) the gut is more responsive to amino acids compared to 5% dextrose, and (3) ileal 30% dextrose infusion leads to remote effects in the proximal gut, perhaps mediated by hormonal or neurovascular factors.