Autoradiographic localization of autonomic receptors in airway smooth muscle. Marked differences between large and small airways.

Autoradiographic methods were used to determine the distribution of autonomic receptors in airway smooth muscle of ferret from trachea to terminal bronchioles; [3H]dihydroalprenolol, [3H]prazosin, and [3H]quinuclidinyl benzilate were used to label beta-adrenergic, alpha-adrenergic, and muscarinic receptors, respectively, using experimental conditions that gave maximal specific receptor binding. Marked differences were found in the longitudinal distribution of each receptor and in distribution of the various receptors in each caliber airway. Beta-receptors were present in high density throughout the airways, with the highest density in bronchioles. Alpha-receptors were sparse in large airways, but numerous in small bronchioles, whereas cholinergic receptors were numerous in bronchial smooth muscle, sparse in proximal bronchioles, and almost absent from distal bronchioles. This method may be useful in studying alterations of autonomic receptors distribution in small and large airways after experimental manipulation and in disease.