Stimulation by capsaicin of gastric alkaline secretion in anesthetized rats

Effects of mucosal application of capsaicin on alkaline secretion were examined in the stomachs of anesthetized rats and compared with those in the duodenum. The stomach (acid secretion was inhibited by omeprazole given i.p.) or the duodenum was perfused with saline (pH 4.5); both the pH of the perfusate and transmucosal potential difference (PD) were continuously monitored; and the HCO3- output was determined by the pH change. Under these conditions, the mucosal application of capsaicin (0.3-6 mg/ml for 30 min) caused significantly increased pH and HCO3- output in a concentration-related manner in both tissues, while PD increased in the duodenum and decreased in the stomach. The HCO3- stimulatory action of capsaicin was markedly attenuated by sensory deafferentation, significantly mitigated by prior administration of indomethacin, and exhibited a marked tachyphylaxis after the repeated exposure at a high concentration (6 mg/ml). None of these treatments had any effect on the pH, PD and HCO3- responses induced by prostaglandin E2 (300 micrograms/kg, i.v.) in these tissues. These results indicate that mucosal application of capsaicin increased the gastroduodenal HCO3- output by stimulation of capsaicin-sensitive sensory neurons. This action may be in part mediated by endogenous prostaglandins.