Cysteamine-induced inhibition of acid neutralization and the increase in hydrogen ion back-diffusion in duodenal mucosa

To investigate the possible impairment of defensive mechanisms in cysteamine-induced duodenal ulceration, the effect of cysteamine on the neutralization of acid by the duodenum and the back-diffusion of hydrogen ions into the duodenal mucosa has been studied. The results obtained were as follows. (1) The intraduodenal pH started to decrease between 3 and 4 hr after cysteamine injection. (2) By perfusion of the duodenal loop excluding the opening of bile and pancreatic ducts, the amount of hydrogen ions (H⁺) neutralized was found to be significantly lower in cysteamine-treated animals than in the controls. (3) the back-diffusion of luminal H⁺ into the duodenal mucosa, estimated by measuring the H⁺ disappearance from the test solution including 100 mM HCl, was significantly increased by cysteamine. From these findings, it has been concluded that cysteamine reduces the resistance of duodenal mucosa to acid coming from the stomach.