Binding of agonists and antagonists to the porcine adipose tissue β-adrenergic receptor(s)

1. Affinities of agonists for porcine adipose tissue β-adrenergic receptors, determined by competitive ligand binding with 3H-dihydroalprenolol to crude adipose tissue membranes in vitro, varied from 50 times > to 25 times < than isoproterenol. Affinities for antagonists varied from 8 times > to 1000 times < propranolol. 2. Receptor affinity was not related to the ability to stimulate or inhibit lipolysis, or to the agonist or antagonist purported receptor subtype specificity. 3. Modeling of ligand-binding data indicated more than one binding site for several ligands. The assignment of β-adrenergic subtypes to the individual binding sites was unclear because this would depend on the individual ligands used to establish binding sites.