TACHYKININ-MEDIATED INCREASE IN MOTILITY ACTS INDEPENDENTLY OF VASOACTIVE INTESTINAL POLYPEPTIDE RELEASE IN THE CANINE ILEUM

Tachykinins induce motor activity in the canine ileum, and their mecha nism of excitation may include inhibition of the release of a nonadren ergic, noncholinergic inhibitor, for which vasoactive intestinal polyp eptide (VIP) is a candidate. Both substance P and neurokinin A produce d a dose-dependent increase in ileal contractility with no significant change in VIP output. The highly selective NK1 agonist [Sar(9), Met(O -2)(11)]substance P and the highly selective NK2 agonist [Nle(10)]neur okinin A (4-10) also increased motor activity in the absence of any ch ange in VIP released. These data suggest that the tachykinins produce motor activity in the canine ileum via a mechanism that does not invol ve changes in VIP output but may involve excitation through both NK1 a nd NK2 receptors.