Gastric mucosal protection by acetazolamide derivatives: role of carbonic anhydrase and sulfhydryls

Acetazolamide, a carbonic anhydrase inhibitor, prevents acute gastric hemorrhagic lesions induced by ethanol. We used acetazolamide and other carbonic anhydrase inhibitors to correlate their gastroprotective effects with the degree of inhibition of carbonic anhydrase. Since acetazolamide is a thiadiazole, we also investigated structurally related thiadiazoles that contain sulfhydryls to test the hypothesis that the protection against ethanol-induced gastric erosions is related to the presence of sulfhydryls. Dose-response studies with acetazolamide revealed that the protection did not correlate with the inhibition of carbonic anhydrase in the rat gastric mucosa. The carbonic anhydrase inhibitors sulfanilamide and ethoxzolamide, did not offer protection. Bismuthiol I, a thiadiazole with two sulfhydryls, was twice as protective as 2-amino-5-mercapto-1,3,4-thiadiazole with only one sulfhydryl group. We conclude that the protection by acetazolamide against ethanol-induced lesions is not related to the inhibition of carbonic anhydrase in the gastric mucosa. The gastroprotective effect of acetazolamide and its derivatives may be related to their content of sulfhydryls in an oxidized or reduced state.