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Abstract
It has been reported that low concentrations of vasoactive intestinal peptide (VIP) suppress the release of acetylcholine (ACh) from vagal nerve terminals. However, there is little documentation of the neuro-effector transmission of VIP in human airways. In the present study, the effects of VIP on excitatory neuro-effector transmission in the human bronchus were investigated, in comparison with feline trachea. In feline trachea, VIP (10(-10) to 10(-7) M) reduced the amplitude of contractions evoked by field stimulation in the presence of indomethacin (10(-6) M). By contrast, VIP (10(-10) to 10(-9) M) had no effect on ACh-sensitivity of smooth muscle cells. These results indicate that VIP in low concentrations has a pre-junctional action inhibiting excitatory neuro-effector transmission, in addition to a post-synaptic action, presumably suppressing transmitter release from the vagal nerve terminals. On the other hand, in human bronchi, VIP (10(-9) to 10(-7) M) did not affect either contractions evoked by field stimulation or those evoked by ACh. These results indicate that VIP does not exhibit any pre-junctional effects in the human bronchus at these concentrations.
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