[Vasoactive intestinal peptide inhibits vagal neuro-effector transmission in feline airway smooth muscle but not in humans].

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.