Acid-induced Mesenteric Hyperemia in Rats: Role of CGRP, Substance P, Prostaglandin, Adenosine, and Histamine

Intraduodenal acidification produces a mesenteric hyperemia that is mediated in part by mucosal capsaicin-sensitive afferent nerves and the bradykinin B2 receptor in anesthetized rats. We hypothesized that novel mechanisms mediated by substance P, adenosine, and histamine1 receptors are involved. Confirmation of a role for calcitonin gene-related peptide (CGRP) but not endogenous prostaglandin was also sought. In study 1, vehicle or antagonists (CGRP(8-37), CP 96345) was administered intravenously. Capsaicin or acid was administered intraduodenally, followed by intravenous CGRP or substance P. In study 2, pretreatments included indomethacin, 8-phenyltheophylline, pyrilamine, or the respective vehicles. Acid was then administered intraduodenally. In both studies, superior mesenteric artery blood flow was monitored. In study 1, the antagonists significantly attenuated capsaicin- and acid-induced mesenteric hyperemia. In study 2, the pretreatments did not alter acid-induced hyperemia. The data confirmed the role of CGRP and indicated for the first time an involvement for substance P in acid-induced mesenteric hyperemia.