Nonadrenergic, noncholinergic nerves are the predominant inhibitory nervous pathway in human airway smooth muscle, and there is evidence in animals that the major neurotransmitter of this system is vasoactive intestinal peptide (VIP). We have investigated the effect of VIP on bronchomotor tone and bronchial responsiveness to inhaled histamine in 6 atopic asthmatic subjects. The VIP was given by inhalation to avoid any indirect effects on the airways that might arise from the potent cardiovascular actions of this peptide when given systemically...
We conclude that VIP protects against histamine-induced bronchoconstriction in human airways in vivo, and therefore has the capacity to be the neurotransmitter of nonadrenergic, noncholinergic inhibitory nerves in human airway smooth muscle.