Responses to the beta 2-selective agonist procaterol of vascular and atrial preparations with different functional beta-adrenoceptor populations.
Relaxant responses to the beta-adrenoceptor agonist, procaterol, have been examined on preparations of guinea-pig pulmonary artery (beta 2-adrenoceptors only), rat and rabbit pulmonary artery and rat aorta (beta 2 greater than beta 1), and these responses have been compared with responses of dog left circumflex coronary artery (beta 1 only). Low concentrations of procaterol (3 nM to 100 nM) relaxed KC1-contracted preparations of rat aorta and pulmonary artery from rat, rabbit and guinea-pig whereas high concentrations (greater than 1 microM) were required to relax preparations of the dog left circumflex coronary artery. The dissociation constant (KP value) for procaterol on beta 1-adrenoceptors was 4.9 microM (determined on dog coronary artery) and on beta 2-adrenoceptors was 0.008 microM (rabbit pulmonary artery). Procaterol therefore had a beta 2:beta 1 selectivity value of 612. KP values obtained on guinea-pig atria for procaterol, on which the concentration-response curve was biphasic, confirmed that both beta 2- and beta 1-adrenoceptors mediate responses of this tissue. The KP values were 0.009 microM (data from the first phase of the control concentration-response curve) and 3.5 microM (data from the concentration-response curve in the presence of the beta 2-selective antagonist, ICI 118,551, 10 nM). Data obtained on rat atria indicated that chronotropic responses of preparations from some rats, but not others, involved a minor population of beta 2-adrenoceptors, but the beta 2-adrenoceptors, when present, were less important than in guinea-pig atria. 6 Procaterol appears to be a particularly useful drug for detecting a functional population of beta 2-adrenoceptors in tissues, whether they are the minor or the predominant receptor sub-type present.
O'Donnell
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D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000187:drug effects; D001262:Atenolol / Q000494:pharmacology; D003331:Coronary Vessels / Q000187:drug effects; D004983:Ethanolamines / Q000494:pharmacology*; D005260:Female; D005280:Fenoterol / Q000494:pharmacology; D006168:Guinea Pigs; D006325:Heart Atria / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D017265:Procaterol; D011651:Pulmonary Artery / Q000187:drug effects; D011817:Rabbits; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*
D000318:Adrenergic beta-Agonists; D004983:Ethanolamines; D011943:Receptors, Adrenergic, beta; D005280:Fenoterol; D001262:Atenolol; D007545:Isoproterenol; D009638:Norepinephrine; D017265:Procaterol