Effects of KB-5492, a New Anti-ulcer Agent with a Selective Affinity for the Sigma-receptor, on Aspirin-induced Disruption of the Rat Gastric Mucosal Barrier

The effect of KB-5492, a new anti-ulcer agent with a selective affinity for the sigma-receptor, on aspirin-induced disruption of the gastric mucosal barrier was studied in rats. Intragastric instillation of aspirin at 200 mg/kg rapidly decreased the gastric transmucosal potential difference (PD) in anesthetized rats. The PD recovered gradually following the removal of aspirin from the instillation solution. Aspirin, administered orally at 200 mg/kg, also reduced the amount of gastric covering mucus and induced a decrease in gastric H+ concentration and an increase in gastric Na+ concentration in pylorus-ligated rats. KB-5492, administered intraduodenally at 200 mg/kg, significantly prevented the aspirin-induced decrease in PD and accelerated the recovery of PD. In addition, KB-5492 at 200 mg/kg significantly prevented the reduction of gastric covering mucus, the decrease in gastric H+ concentration and the increase in gastric Na+ concentration induced by aspirin. These effects were similar to those of 0.01 mg/kg of 16,16-dimethyl prostaglandin E2 (dmPGE2). Teprenone at 200 mg/kg did not show any effect except for the inhibitory effects on the changes in gastric H+ and Na+ concentration. In the histological study, marked reduction of PAS-positive epithelial mucus and the exfoliation of surface epithelial cells were observed in the gastric mucosa exposed to aspirin. KB-5492 and dmPGE2 almost completely prevented the former, whereas both drugs prevented the latter incompletely. These findings indicate that KB-5492 protects the gastric mucosal barrier against the disruption by aspirin, which may be mainly exerted by retention of the gastric covering mucus.