TY - JOUR T1 - Coexistence of <em>Beta</em><sub>1</sub> and <em>Beta</em><sub>2</sub> Adrenoceptors in Mammalian Lung: Evidence from Direct Binding Studies JF - Molecular Pharmacology JO - Mol Pharmacol SP - 996 LP - 1005 VL - 14 IS - 6 AU - E. L. RUGG AU - D. B. BARNETT AU - S. R. NAHORSKI Y1 - 1978/11/01 UR - http://molpharm.aspetjournals.org/content/14/6/996.abstract N2 - [3H]Dihydroalprenolol ([3H]DHA) binds to rat and rabbit lung membranes with a dissociation equilibrium constant (Kd) of about 0.5 nM and displays binding characteristics indicative of an interaction with beta adrenoceptors. The density of beta adrenoceptor binding sites was greater in rat than rabbit lung membranes, though the binding sites from both species had very similar affinities for nonselective agents such as (-)isoproterenol, (-)epinephrine, and (-)timolol, and exerted a similar degree of stereoselectivity between the isomers of propranolol. On the other hand, the affinity of beta1 selective agents such as (±)practolol, (±)atenolol, and (-)norepinephrine was greater in rabbit lung membranes whereas the beta2 agonist (-)erythro procaterol (OPC-2009) was considerably more potent on membranes prepared from rat lung. However, detailed analysis of the competition curves displayed by the beta1 and beta2 selective drugs strongly suggest that beta1 and beta2 adrenoceptor binding sites coexist in different proportions within lung tissue in the two species (rat 25%, beta1; 75% beta2; rabbit 60%, beta1; 40% beta2). The significance of these findings to the effects of catecholamines on pulmonary function is discussed. ACKNOWLEDGMENTS We would like to thank Miss Jenny Bell for preparing the manuscript. ER -