ROLE OF CAPSAICIN-SENSITIVE AFFERENT NEURONS IN MUCOSAL BLOOD-FLOW RESPONSE OF RAT STOMACH INDUCED BY MILD IRRITANTS

The role of capsaicin-sensitive sensory nerves in gastric mucosal blood flow (GMBF) responses to mild irritants was investigated in the rat stomach mounted on a lucite chamber using hypertonic NaCl and 0.2 N HCl. Exposure of the mucosa to hypertonic NaCl (0.5, 0.75, 1 M) for 10 min caused a reduction in the transmucosal potential difference (PD) in a concentration-related manner, followed by an increase of luminal pH and GMBF. In contrast, mucosal application of 0.2 N HCl caused no or little change in PD and pH, but increased GMBF significantly. Functional ablation of capsaicin-sensitive sensory nerves significantly inhibited the increase of GMBF after exposure to these irritants, although the PD and pH responses induced by 1 M NaCl remained unaltered by this treatment. Pretreatment with indomethacin (5 mg/kg, subcutaneously) significantly attenuated the GMBF responses to 1 M NaCl and 0.2 N HCl and inhibited the increase of pH caused by 1 M NaCl. Mucosal application of capsaicin (0.1 mg/ml for 10 min) produced an increase of GMBF without being accompanied by change in PD and pH, and this effect was significantly blocked by either indomethacin or chemical deafferentation. These results suggest that capsaicin-sensitive sensory nerves as well as endogenous prostaglandins may be involved in the mechanism of GMBF responses induced by mild irritants, and the latter might sensitize these nerves to mucosal irritation. PD reduction may be obligatory for pH but not GMBF responses.