MECHANISM OF INTRAGASTRIC NICOTINE PROTECTION AGAINST ETHANOL-INDUCED GASTRIC INJURY

To elucidate the mechanism of intragastric nicotine protection against ethanol-induced gastric mucosal injury seen in a previous report and in our preliminary study, the following studies were performed. Rats were pretreated with naloxone (8 mg/kg intraperitoneal, 0.5 hr prior to study) to block opiate receptors; or capsaicin (125 mg/kg subcutaneous 10 days prior to study) to denervate the afferent sensory fibers; or indomethacin (2.5 mg/kg intragastric or 5 mg/kg subcutaneous, 1 hr prior to study) to inhibit endogenous prostaglandin synthesis. At 1-hr intervals, nicotine (4 mg/kg) or vehicle and 40% ethanol were then given intragastrically. Total gastric corpus mucosal lesion length was measured unbiasedly. In separate studies, gastric mucosal blood flow (GMBF) was assessed by hydrogen gas clearance before and after intragastric nicotine or vehicle; luminal mucus volume, gastric juice volume, and acid output were measured 1 hr after either intragastric nicotine or vehicle administration. The results showed that the acute protective effect of intragastric nicotine was associated with a significantly larger luminal mucus volume. It was not blocked by naloxone, capsaicin, or indomethacin. There was no increase in GMBF. The larger gastric residual volume did not account for the protection. We conclude that the mechanism mediating nicotine protection is unique and is independent of opiate receptors, capsaicin-sensitive afferent sensory nerve fibers, endogenous prostaglandin generation, or dilution of the injurious agent. The increase in luminal gastric mucus volume may contribute to the protective effect of intragastric nicotine against gastric mucosal injury produced by 40% ethanol.