Characterization and Autoradiographic Distribution of the β-Adrenergic Receptor in the Rat Lung

An unexpected distribution of the beta-adrenergic receptor in the rat lung was revealed by an autoradiographic technique. [3H]-Dihydroalprenolol binding was stereoselective. L-propranolol was 300 times more potent than D-propranolol in competition experiments. Scatchard analysis revealed a Kd of 1.1 nM and Bmax of 14 fmol/mg wet weight. Relative potencies of beta-adrenergic ligands were: propranolol greater than alprenolol greater than timolol greater than pindolol greater than isoproterenol greater than epinephrine greater than soterenol greater than metoprolol greater than terbutaline greater than norepinephrine. The autoradiograms generated revealed a diffuse pattern with binding always associated with tissue structures. We conclude that beta-adrenergic receptors are extensively distributed in the lung, being present in large and small airways and blood vessels.