MYOELECTRIC PATTERN AND EFFECTS ON SMALL-BOWEL TRANSIT INDUCED BY THETACHYKININS 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 intesti nal transit of a radioactive marker in fasted conscious rats. Myoelect ric activity was recorded using bipolar electrodes implanted at 5, 20 and 35 cm distal to pylorus. Intravenous infusions of neurokinin A, ne urokinin B and neuropeptide K at doses of 50-200 pmol kg-1 min-1, and substance P at doses of 100-300 pmol kg-1 min-1, disrupted migrating m yoelectric 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 spiki ng induced by the tachykinins was associated with increased transit of the marker in animals receiving neurokinin A and neurokinin B, but no t substance P and neuropeptide K. We conclude that the tachykinins act ivate the smooth muscle layers of the small intestine in the rat by me chanisms involving neurokinin receptors, but not muscarinic, nicotinic or H-1-receptors. Our results suggest a role for tachykinins in regul ation of motility by induction of irregular spiking, which may stimula te transit through the small intestine.