title: The beta 1-adrenoceptor antagonist CGP 20712 A unmasks beta 2-adrenoceptors activated by (-)-adrenaline in rat sinoatrial node.
abstract: The role of sinoatrial beta 1- and beta 2-adrenoceptors mediating positive chronotropic effects of (-)-adrenaline and (-)-noradrenaline was investigated in rat right atria. Concentration effect curves for (-)-adrenaline, but not for (-)-noradrenaline, became biphasic in the presence of the beta 1-adrenoceptor antagonist CGP 20712 A. The curves for (-)-adrenaline in the presence of 300 nmol/l CGP 20712 A (equivalent to 1,000 times its KB, KB = 0.3 nmol/l for beta 1-adrenoceptors) comprise a high-sensitivity component that saturates at 1/4 of maximum effect, and a low sensitivity component. The high-sensitivity component is blocked by the beta 2-adrenoceptor-selective antagonist ICI 118,551. These results are consistent with an involvement in the rat of both beta 1-adrenoceptors (to a major extent) and beta 2-adrenoceptors [only at high (-)-adrenaline concentrations] in the positive chronotropic effects of (-)-adrenaline. (-)-Noradrenaline appears to activate mostly rat sinoatrial beta 1-adrenoceptors.
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D002395:Catecholamines / Q000494:pharmacology*; D004837:Epinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*; D012849:Sinoatrial Node / Q000187:drug effects*
chemical_list: D000319:Adrenergic beta-Antagonists; D002395:Catecholamines; D007093:Imidazoles; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; C026777:ICI 118551; C049763:CGP 20712A; D009638:Norepinephrine; D004837:Epinephrine