Myoelectric pattern and effects on small bowel transit induced by the tachykinins neurokinin A, neurokinin B, substance P and neuropeptide K in the rat

Effects of neurokinin A, neurokinin B, substance P and neuropeptide K on myoelectric activity in the small intestine were related to intestinal transit of a radioactive marker in fasted conscious rats. Myoelectric activity was recorded using bipolar electrodes implanted at 5, 20 and 35 cm distal to pylorus. Intravenous infusions of neurokinin A, neurokinin B and neuropeptide K at doses of 50–200 pmol kg −1 min −1 and substance P at doses of 100–300pmol kg −1 min −1 , disrupted migrating myoelectric complexes and induced irregular spiking. These effects were not prevented by atropine, hexamethonium or mepyramine. However, the effect of neurokinin A was attenuated by spantide. The irregular spiking induced by the tachykinins was associated with increased transit of the marker in animals receiving neurokinin A and neurokinin B, but not substance P and neuropeptide K. We conclude that the tachykinins activate the smooth muscle layers of the small intestine in the rat by mechanisms involving neurokinin receptors, but not muscarinic, nicotinic or H 1 ‐receptors. Our results suggest a role for tachykinins in regulation of motility by induction of irregular spiking, which may stimulate transit through the small intestine.