Tachykinin-mediated increase in motility acts independently of vasoactive intestinal polypeptide release in the canine ileum
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Tachykinins induce motor activity in the canine ileum, and their mechanism of excitation may include inhibition of the release of a nonadrenergic, noncholinergic inhibitor, for which vasoactive intestinal polypeptide (VIP) is a candidate. Both substance P and neurokinin A produced a dose-dependent increase in ileal contractility with no significant change in VIP output. The highly selective NK1 agonist [Sar9, Met(O2)11]substance P and the highly selective NK2 agonist [Nle10]neurokinin A (4-10) also increased motor activity in the absence of any change in VIP released. These data suggest that the tachykinins produce motor activity in the canine ileum via a mechanism that does not involve changes in VIP output but may involve excitation through both NK1 and NK2 receptors.
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