Effect of luminal acid on gastric and duodenal bicarbonate transport.

Epithelial HCO3 transport by stomach and duodenum is influenced by luminal pH. Acid itself, but not stimulants of gastric HCl secretion, increase mucosal alkaline secretion in a variety of in vitro and in vivo systems. Using pairs of amphibian mucosa, both gastric and proximal duodenal HCO3 transport was stimulated by low luminal pH. This response displayed some tissue specificity and operates by a humoral mechanism. In the anaesthetized cat, the increase in duodenal epithelial HCO3 secretion following exposure of the lumen to acid (pH2) is probably independent of luminal Cl-. Low luminal pH in the stomach did not influence HCO3 secretion by the duodenum either in vitro or in vivo. The process of acid-stimulated epithelial HCO3 transport may be important in maintaining H+ ion disposal in the upper gastrointestinal tract in response to low luminal pH.