MODULATION OF AUTOREGULATORY ESCAPE BY CAPSAICIN-SENSITIVE AFFERENT NERVES IN RAT STOMACH

Visceral C fibers are stimulated by ischemia and hypoxia, which can be produced by intense vasoconstriction. Epinephrine applied to the gastric submucosa produces a marked vasoconstriction followed by autoregulatory escape. We hypothesize that the autoregulatory escape from epinephrine-induced vasoconstriction in the rat stomach is mediated partly by capsaicin-sensitive C fibers. Functional ablation of these afferent fibers by high-dose systemic capsaicin pretreatment will significantly reduce the magnitude of the autoregulatory escape. Rats received capsaicin (125 mg/kg sc) 10 days before blood flow studies to produce functional impairment of the capsaicin-sensitive afferent nerves. Control rats received vehicle. Under urethan anesthesia, a small area (2 mm diam) of the serosa from the anterior gastric wall was removed to expose the submucosa. The tip of a side-viewing laser-Doppler flow probe was placed inside the stomach directly beneath the exposed submucosa. At 20-min intervals, 20-mu-l of buffer, 5 x 10(-4) M epinephrine, 1.6 x 10(-4) M capsaicin, or 3.3 x 10(-2) M histamine was applied topically to the exposed submucosa, with saline washes between applications at 10 min after each application. Blood pressure and laser-Doppler flow signals were monitored continuously. The escape index during the period of epinephrine application was significantly lower in the capsaicin-pretreated rats (0.239 +/- 0.046) than in the vehicle-pretreated rats (0.474 +/- 0.079). Functional ablation of the capsaicin-sensitive afferent fibers was confirmed by a significant blockade of the vasodilatation induced by topical capsaicin. Histamine-induced vasodilatation was unaffected. The data are consistent with the hypothesis that the capsaicin-sensitive afferent nerves mediate in part the autoregulatory escape from epinephrine-induced vasoconstriction in the rat stomach.