[Bronchial hyperreactivity: neurogenic factors].

Over the last fifty years, the role of neurogenic factors in asthma and bronchial hyperreactivity has been intensively investigated. The roles of the cholinergic and adrenergic nervous systems have been clarified and several sub-types of muscarinic receptors identified. The localisation and functions of both muscarinic and adrenergic receptors have been further specified. It has also been shown that afferent nerve fibers as well as sympathetic and parasympathetic nerve fibers secrete various neuropeptides. The physiological role of these peptides is not yet known but it appears that they have a powerful effect on bronchial smooth muscle tone, microvascular permeability, mucus secretion and secretion of mediators by inflammatory cells. The results of numerous studies suggest that there are several abnormalities in the adrenergic and cholinergic nervous systems of asthmatic patients, but that these abnormalities are not themselves the cause of bronchial hyperreactivity. They may however contribute to enhance it. The role of the various newly identified neuropeptides in the genesis and maintenance of bronchial hyperreactivity remains to be determined.