The affinity and efficacy of naturally occurring catecholamines at beta-adrenoceptor subtypes

• Published in: Journal of pharmacy and pharmacology Vol. 37; no. 7; p. 499
• Main Authors: McPherson, G A, Molenaar, P, Malta, E
• Format: Journal Article
• Language: English
• Published: England 01.07.1985
• Subjects: Animals; Catecholamines - metabolism; Epinephrine - metabolism; Female; Guinea Pigs; In Vitro Techniques; Isoproterenol - pharmacology; Muscle Contraction - drug effects; Muscle Relaxants, Central - pharmacology; Myocardial Contraction - drug effects; Norepinephrine - metabolism; Potassium - pharmacology; Receptors, Adrenergic, beta - metabolism; Uterine Contraction - drug effects
• ISSN: 0022-3573
• DOI: 10.1111/j.2042-7158.1985.tb03051.x

The contribution of affinity and efficacy to the agonistic actions of the naturally occurring catecholamines, (-)-noradrenaline and (-)-adrenaline at beta-adrenoceptor sites were assessed in guinea-pig driven left atrial (beta 1) and K+-depolarized uterine (beta 2) preparations. The dissociation constants of each agonist, required in these calculations, were calculated using radioligand binding techniques. [125I]Iodocyanopindolol bound to sites in membrane preparations of each tissue which have been shown to represent beta 1-(atria) and beta 2-(uterus) adrenoceptors. It was found that (-)-noradrenaline was approximately 10-fold more selective for the beta 1- as opposed to the beta 2-adrenoceptor in the pharmacological studies. Affinity/efficacy calculations indicated that this selectivity was entirely due to a selective affinity for the beta 1-adrenoceptor subtype. (-)-Noradrenaline, (-)-adrenaline and the reference compound (-)-isoprenaline all had approximately the same efficacy at either beta-adrenoceptor subtype.