REGIONAL AND INTERSPECIFIC DIFFERENCES IN THE LIGAND-BINDING PROPERTIES OF BETA-ADRENERGIC RECEPTORS OF INDIVIDUAL WHITE ADIPOSE-TISSUE DEPOTS IN THE SHEEP AND RAT

The ligand binding of beta-adrenergic receptors was characterized in the omental, subcutaneous and popliteal adipose tissue depots in the sheep, and the lumbar and parametrial depots in the rat. Displacement of [I-125]iodocyanopindolol ([I-125]ICYP) binding to sheep adipose tissue membranes by the beta-adrenergic antagonists CGP 20712A and ICI 118,551 (beta-1- and beta-2-antagonists, respectively) suggested only a single ligand binding site predominantly beta-2 in character in all three depots, but revealed differences in affinity for these ligands between depots. Lactation increased beta-receptor ligand binding in subcutaneous and omental but not popliteal sheep adipose tissue depots, but had no effect on beta-adrenergic receptor affinities for CGP 20712A and ICI 118,551 in the three sheep adipose tissue depots studied. In rat adipocyte membranes, displacement of [I-125]ICYP by CGP 20712A and ICI 118,551 was biphasic, indicating high and low affinity sites; displacement profiles differed markedly between lumbar and parametrial depots, the former having a preponderance of beta-1-like receptors and the latter a preponderance Of beta-2-like receptors. The properties of the beta-adrenergic receptor binding site thus show species and depot specific differences.