Tachykinin NK1 receptors mediate atropine-resistant net aboral propulsive complexes in porcine ileum.

Background: We studied the effects of tachykinin receptor antagonists on fluid-induced, spontaneous net aboral propulsive complexes in isolated, vascularly perfused porcine ileal segments.
Methods: Fluid was instilled at a constant rate into the proximal opening of the segment, resulting in regular, rapidly propagating propulsive complexes along the entire ileal segment in the aboral direction.
Results: NKI, NK2 or NK3 receptor antagonists (CP99994, SR48968 and SR 142801 all at 10(-6) M) had no effect on the frequency of propulsive complexes. Atropine (10(-6) M) abolished the propulsive complexes for 15.0 +/- 1.3 min (n = 18). In spite of continued atropine infusion, the propulsive complexes reappeared. Infusion of the NK1 receptor antagonist CP99994 (10(-6) M) during continued atropine infusion blocked net aboral propulsive complexes in 5 experiments for 12.2 +/- 2.4 min and resulted in motor paralysis in 2 experiments. SP release, measured in the venous effluent, was significantly increased in relation to propulsive complexes during atropine infusion.
Conclusion: We conclude that, in the porcine ileum, tachykinins mediate atropine-resistant net aboral propulsive complexes acting on NKI receptors.