The respiratory effects of neuropeptides.

Several peptides have been localised to pulmonary nerves and endocrine cells. The neuropeptides vasoactive intestinal polypeptide (VIP) and substance P have potent effects on the airway smooth muscle, bronchial glands and blood vessels. There is increasing evidence that VIP and substance P are neurotransmitters of the non-adrenergic, non-cholinergic nervous (NANC) system. Non-adrenergic inhibitory nerves are the predominant inhibitory nervous system of the human airways. The presence of VIP in the innervation of the airways and the demonstration that it can mimick the effect of NANC nerve stimulation supports the hypothesis that it could be a mediator of the NANC system in the lungs. Sensory nerve fibers containing substance P can contribute to the smooth muscle contraction and mucosal oedema seen in asthma, by local axon reflexes that are initiated by noxious stimuli, such as for example cigarette smoke. A rat model for study of the bronchial reaction to substance P and related tachykinins, is described. In addition to a direct effect on airway smooth muscle, a large part of the broncho-constrictory actions of tachykinins in the rat is mediated by interaction with cholinergic nerves.