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Xamoterol activates beta 1 but not beta 2 adrenoceptors in mammalian myocardium comparison of its affinity for beta 1 and beta 2 adrenoceptors coupled to the adenylate cyclase in feline and human ventricle with positive inotropic effects



Xamoterol activates beta 1 but not beta 2 adrenoceptors in mammalian myocardium comparison of its affinity for beta 1 and beta 2 adrenoceptors coupled to the adenylate cyclase in feline and human ventricle with positive inotropic effects



Journal of Cardiovascular Pharmacology 13(1): 105-117



The mode of action of xamoterol, a .beta.1-selective partial agonist, was investigated in feline myocardium. Xamoterol bound with an 18-fold greater affinity to ventricular .beta.1-adrenoceptors (labeled with [3H](-)-bisoprolol) than to .beta.2-adrenoceptors (labeled with [3H]ICI 118,551). Xamoterol had a 10-20-fold higher affinity for ventricular .beta.1-adrenoceptors coupled to the adenylate cyclase than for cyclase-coupled .beta.2-adrenoceptors. The intrinsic activity of xamoterol with respect to (-)-norepinephrine was 0.5 in right ventricular papillary muscles (force), 0.6 in left atria (force); 0.6 in right atria (sinoatrial rate) and 0.1-0.2 in ventricular membranes (cyclase). The stimulant effects of xamoterol were antagonized by .beta.1-specific CGP 20,712 A but not by .beta.2-selective ICI 118,551. Xamoterol activated only .beta.1-adrenceptors, while (.beta.2-adrenoceptors occupied by xamoterol remained silent. The positive inotropic effects of a nearly maximally effective xamoterol concentration were associated with a considerably greater .beta.1-mediated cyclase stimulation than the same inotropic effect of (-)-norepinephrine. In human ventricular membranes xamoterol stimulated marginally the adenylate cyclase and antagonized the effects of (-)-norepinephrine with a 30-fold greater affinity for .beta.1- than for .beta.2-adrenoceptors.

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Accession: 008007921

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PMID: 2468921


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