Interaction of an aluminum-magnesium containing antacid and gastric mucus: possible contribution to the cytoprotective function of antacids.

Antacids are generally thought to protect the gastric mucosa from damage primarily by their ability to neutralize hydrochloric acid, but recently other mechanisms of antacid cytoprotection have been suggested. The aim of our study was to determine if the antacid hydrotalcit (Mg6Al2(OH)16CO3 x 4H2O) and its clinical formulations Talcid (suspension and tablet) can influence the acid barrier properties of pig gastric mucus (PGM). Viscosities, flow patterns of injected HCl, and permeability to HCl were assayed in solutions of PGM with and without added antacid. Talcid-suspension markedly increased mucin viscosity between pH 2 and 7. In contrast, powdered Talcid-tablet and hydrotalcit noticeably reduced mucin viscosity at pH 5 and below. HCl barely diffused through PGM-Talcid-suspension, whereas the acid was able to quickly penetrate a PGM-Talcid-tablet powder or PGM-hydrotalcit mixture. When injected into a mixture of PGM-Talcid-suspension, HCl travelled in a single distinct channel whereas in both PGM-Talcid-tablet powder or PGM-hydrotalcit mixtures, the acid mixed irregularly throughout. Experiments with antacids alone revealed that Talcid-suspension, but not Talcid-tablet nor hydrotalcit, had barrier properties similar to PGM. Talcid-suspension has viscoelastic features similar to gastric mucin and may afford mucosal protection by its ability to maintain or mimic the barrier properties of gastric mucus gel. In contrast, powdered Talcid-tablets and hydrotalcit reduce the barrier function of gastric mucus.