Putative mechanisms of cytoprotective effect of certain antacids and sucralfate. An investigation of cytoprotective activity of certain antacids and inert particles was carried out by treating ethanol-induced gastric mucosal damage in rats in order to clarify possible mechanisms by which aluminum-containing antacids act. Al(OH)3 inhibited gastric mucosal damage in a dose-related and time-dependent manner. Neither aluminum ions themselves nor the particle size of the Al(OH)3 complex were responsible for the observed cytoprotection, since neither AlCl3, chemically inert Al2O3*C, nor sea sand showed protective effects. Hyperosmolality in the gastric lumen was not a deciding factor in inducing cytoprotection. Silicic acid and titanium dioxide, with superficial charge similar to Al(OH)3 proved to be effective in inhibiting gastric hemorrhagic lesions and releasing PGE2, suggesting that the surface charge of Al(OH)3 may be important in its cytoprotective properties. The same may also be valid for sucralfate. Since antacid-induced cytoprotection was only partly reduced by pretreatment with indomethacin, it is likely that additional mechanisms and mediators other than prostaglandins, such as nonprotein sulfhydryls, also are involved in gastric cytoprotection arising from aluminum-containing antacids. 