RESPONSES TO THE BETA-2-SELECTIVE AGONIST PROCATEROL OF VASCULAR AND ATRIAL PREPARATIONS WITH DIFFERENT FUNCTIONAL BETA-ADRENOCEPTOR POPULATIONS

  • 1 January 1985
    • journal article
    • research article
    • Vol. 84  (1) , 227-235
Abstract
Relaxant responses to the .beta.-adrenoceptor agonist, procaterol, were examined on preparations of guinea pig pulmonary artery (.beta.2-adrenoceptors only), rat and rabbit pulmonary artery and rat aorta (.beta.2 > .beta.1), and these responses were compared with responses of dog left circumflex coronary artery (.beta.1 only). Low concentrations of procaterol (3 nM-100 nM) relaxed KCl-contracted preparations of rat aorta and pulmonary artery from rat, rabbit and guinea pig whereas high concentrations (> 1 .mu.M) 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 .mu.M (determined on dog coronary artery) and on .beta.2-adrenoceptors was 0.008 .mu.M (rabbit pulmonary artery). Procaterol therefore had a .beta.2:.beta.1 selectively 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 .mu.M (data from the 1st phase of the control concentration-response curve) and 3.5 .mu.M (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. 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.

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