MOLECULAR PHARMACOLOGY, 34:318-326 Subclassification of f3-Adrenergic Receptors of Rat Fat Cells:

Catecholamines regulate lipolysis in rat fat cells via f.-adrenergic receptors. Recently, it has been proposed that $-adrenergic receptors of rat fat cells are neither f nor 132 in character but rather an ‘isoreceptor, ’ ‘hybrid, ’ or $ [Br. J. Pharmacol. 84:1 31-1 37 (1 985)]. This putative receptor subtype has been envisioned as possessing an alkanolamine side-chain interaction site of i3 nature and an aromatic moiety interaction site of f.2 nature. These proposals were evaluated in the present work through a reexamination of the nature of the fat cell /3-adrenergic receptor using four radioligands that differ chemically in one or both of these regions of the molecule as well as in their hydro-phobicity. Equilibrium binding of agonist and of f3- and /32-subtype-selective high affinity antagonist ligands to fat cell mem-branes was detailed. The binding sites labeled by these ligands had the characteristics of /31-adrenergic receptors. The ran