IMPLICATIONS OF NITRIC-OXIDE IN THE ACTION OF CYTOPROTECTIVE DRUGS ON GASTRIC-MUCOSA

Cytoprotective drugs, including sucralfate, colloidal bismuth (De-Nol), aluminium-containing antacids (Maalox), carbenoxolone-like agents (sofalcone), and stable PGE2 analogues (nocloprost), are known to prevent acute gastric mucosal damage induced by topical irritants. This effect is usually accompanied by an elevation in mucosal blood flow. Recently, nitric oxide (NO), a potent vaso-relaxant, has been implicated in gastroprotection by carbenoxolone, the prototype of cytoprotective drugs. In this study we assessed the involvement of NO in acute gastric damage induced by ethanol and in the prevention of this damage by sucralfate, Maalox, De-Nol, sofalcone, and nocloprost. Each of these drugs dose-dependently reduced the formation of ethanol-induced gastric lesions. The optimal gastroprotective dose was used in further studies to check the possible contribution of NO in this protection. Pretreatment with N(G)-nitro-L-arginine (L-NNA) (12.5-50 mg/kg i.v.), an inhibitor of NO synthase, dose-dependently enhanced the mucosal damage by ethanol itself and reduced the protective effects of sucralfate and Maalox but not those of sofalcone, De-Nol or nocloprost against the ethanol injury. Reduction by L-NNA of the mucosa-protective action of sucralfate or Maalox was accompanied by a decrease in gastric blood flow, which was antagonized by L-arginine (a substrate of NO synthase) but not by D-arginine. This study suggests that gastroprotective agents such sucralfate and Maalox, but not sofalcone or De-Nol, activate the NO system that may contribute to mucosal integrity and preservation of mucosal microcirculation.