title: Beta-1 receptor is the predominant beta-adrenoreceptor on rat brown adipose tissue.
abstract: A new in vitro radioligand binding assay is described for brown adipose tissue using the beta adrenergic antagonist [3H]CGP 12177 (4-(3-t-butylamino-2-hydroxypropoxy)-[5,7-3H]benzimidazol-2-one). Binding was saturable and stereoselectively inhibited by propranolol. There was 60 to 80% specific binding using either 30 microM l-isoproterenol or 10 microM l-propranolol to define nonsaturable binding. [3H]CGP 12177 was bound to partially purified membranes from collagenase-separated brown adipocytes with a Kd of 0.84 nM, as determined from kinetic studies, and 1.24 +/- 0.13 nM as found by equilibrium binding studies; maximum binding was 14.2 +/- 0.9 fmol/mg of protein. Membranes from whole-pad homogenates had a similar Kd of 1.17 +/- 0.14 nM but twice the maximum number of binding sites (28.5 +/- 4.4 fmol/mg of protein). Intact brown adipocytes had a Kd of 0.55 nM and a maximum binding of 29.4 +/- 1.5 fmol X 10(-6)/cell or 17,700 sites per cell. Competitive binding studies showed about 80% of the binding sites to be of the beta-1 and 20% of the beta-2 subtype. The pA2 values derived from inhibition of isoproterenol-stimulated in vitro oxygen consumption in intact brown adipocytes by the beta-1 selective antagonist metoprolol and beta-2 selective lCl 118551 were in close agreement with their respective K1 values at the beta-1 receptor as derived from competitive binding studies. These data strongly suggest that the beta-1 adrenoreceptor on brown adipose tissue is primarily responsible for the initiation of thermogenesis in this tissue.
mesh_terms: D002001:Adipose Tissue, Brown / Q000032:analysis* / Q000166:cytology / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D011412:Propanolamines / Q000378:metabolism; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000032:analysis*; D014316:Tritium
chemical_list: D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D014316:Tritium; D007545:Isoproterenol; C033394:CGP 12177; D009638:Norepinephrine