Amino Acids Mediate Postprandial Jejunal Proabsorption

Ingestion of a meal stimulates small intestinal ion and water transport. Current evidence suggests that this response, termed proabsorption, is primarily mediated by the apical Na⁺/glucose cotransporter. Like glucose, the majority of amino acid absorption occurs by Na⁺-dependent, secondary active transport. The purpose of this study was to determine the role of amino acid transport in meal-induced jejunal ion and water absorption in vivo. Exteriorized, neurovascularly intact jejunal loops measuring 25 cm were created in six female mongrel dogs, and the dogs were allowed to recover for 2 weeks. After an overnight fast, the loops were perfused with a standard buffer containing 10 mM aspartate, leucine, glycine, or lysine. Net water and electrolyte absorption before and after a mixed meal was calculated using [¹⁴C]polyethylene glycol as a volume marker. Aspartic acid, leucine, glycine, and lysine are each transported by a separate transporter system. Except for lysine, each amino acid significantly (P < 0.05) potentiated sodium and water absorption after a meal. In addition, this effect was at least as great as that seen with 10 mM glucose. These results demonstrate that amino acid transporter, like the Na⁺/glucose cotransporter, mediates meal-induced jejunal sodium and water absorption and may be as important in the proabsorptive response.