1.   Mucosal resistance was similar in the three groups when the acid challenge was given after saline pretreatment.

2.   Hence, we postulated that adaptive cytoprotection maintains a physiological equilibrium between duodenal mucosal resistance and luminal acidity.

3.   Mucosal resistance to acid was tested in anaesthetised rats by duodenal infusion of graded doses of HCl using a tube implanted in the proximal duodenum.

4.   A second series of experiments tested the mucosal resistance to acid after pretreatment with a mild dose of acid to induce adaptive cytoprotection.

5.   This protocol tested mucosal resistance to acid after mild irritation.

6.   Exposure of the duodenal mucosa to a mild dose of acid significantly enhanced mucosal resistance to a subsequent acid challenge.