ABSTRACT
Autonomic nerves influence airway tone by activating specific receptors on the target cells in the airways. The different components of the autonomic nervous system interact with each other, by affecting release of neurotransmitter, at ganglia in the airways, and by interaction at postjunctional receptors. Muscarinic receptors regulate mucus secretion from both submucosal glands and airway epithelial goblet cells. In the cholinergic pathway, acetylcholine released from postganglionic nerve endings stimulates muscarinic cholinergic receptors. Adrenergic mechanisms include sympathetic nerves that release noradrenaline and circulating adrenaline secreted from the adrenal medulla; these catecholamines activate α- and ß-adrenoceptors. Autoradiographic studies have revealed that ß-receptors are localized to many different cell types within the lung, including smooth muscle of all airways from trachea to terminal bronchioles, submucosal glands, airway epithelium and alveolar walls. Evidence has been found for a ß-receptor-mediated inhibition of cholinergic transmission in human and in dog airways. Changes in ß2-receptor function have been reported to occur in lung diseases, such as asthma.
