Effects of neurotensin on the non-adrenergic inhibitory neurotransmission in the guinea-pig duodenum

The effects of neurotensin on the non-adrenergic inhibitory neurotransmission in the guinea-pig duodenum were investigated. The resting membrane potential of the duodenal smooth muscle cells was reduced by neurotensin at the concentration of 3 X 10(-8) M or more. The amplitude of the non-adrenergic inhibitory potentials was decreased by neurotensin (1-3 X 10(-8) M). In the Ca2+-free solution, the amplitude of the inhibitory potentials was also decreased. The increased amplitude of the non-adrenergic inhibitory potentials evoked in the high calcium solution (Ca2+, 5 mM) was decreased by neurotensin (10(-8) M). Neither atropine (1.4 X 10(-6) M) nor propranolol (3.4 X 10(-6) M) blocked the inhibitory action of neurotensin (10(-8) M) on the inhibitory potential. The frequency of the spontaneous action potentials of the duodenal smooth muscle cells was strongly increased with accompanying depolarization by neurotensin 8 X 10(-8) M. The tonic contraction of the duodenal smooth muscles was produced by neurotensin (3-8 X 10(-8) M). The results obtained suggest that neurotensin relates to the non-adrenergic inhibitory pathway in the control mechanism on intestinal motility.