Localization of β-adrenoreceptors in mammalian lung by light microscopic autoradiography

Abstract

β-Adrenergic agonists regulate a variety of lung functions including relaxation of airway smooth muscle, secretion of mucus¹, release of surfactant² and modulation of mediator release from mast cells³. Assays of the direct binding of radio-labelled β-adrenergic antagonists to homogenates of whole lung from several species have revealed a very high density of β-adrenoreceptors, but the cellular location of these receptors has not been determined^4–7. Using a technique previously used to study distribution of receptors in the brain^8,9 we report here for the first time the localization of β-receptors in the lung by light microscopic autoradiography. Initial biochemical studies showed that ³H-dihydroalprenolol (³H-DHA) bound to slide-mounted frozen sections of ferret lung with the characteristics expected of interaction with β-receptors. Autoradiograms prepared by apposition of dry emulsion-coated coverslips to these sections showed that the distribution of β-receptors in the lung was widespread. The highest concentration of β-receptors was found in smooth muscle of bronchioles with somewhat lower densities in smooth muscle of large airways. Labelling also occurred in airway epithelium, submucosal glands and vascular smooth muscle. Alveolar walls were heavily labelled and as type II pneumocytes, which are known to have β-receptors, comprise only a small portion of the surface area, β-receptors must also be present on type I cells and/or capillary endothelial cells, although their function is at present unknown.