The use of functional antagonism to determine whether beta-adrenoceptor agonists must have a lower efficacy than isoprenaline to be trachea-atria selective in vitro in guinea-pigs.
1 The relative efficacies of three trachea-atria selective beta-adrenoceptor agonists, fenoterol, Me 506 and Me 454, compared to isoprenaline, were determined on both trachea and atria of guinea-pigs. 2 On tracheal preparations the beta-adrenoceptor agonists were used as functional antagonists of carbachol and a comparison of the maximum shifts in the carbachol concentration-response line produced by each of the beta-adrenoceptor agonists provided a comparison of their efficacies. 3 On atrial preparations carbachol was used as a functional antagonist of the beta-adrenoceptor agonists and comparison of the maximum responses to the beta-adrenoceptor agonists in the presence of carbachol provided a comparison of their efficacies. 4 On trachea and atria the order of efficacy of the compounds was Me454 greater than Me506 greater than or equal to isoprenaline=fenoterol. 5. The results indicated that high efficacy in a non-catechol beta-adrenoceptor agonist is possible provided there is a favourable N-substituent group. 6 Since Me 454, Me 506 and fenoterol, which are trachea-atria selective, have effficacies equal to or greater than that of isoprenaline, which is non-selective, it is concluded that low efficacy in a compound is not essential for it to show trachea-atria selectivity in vitro in guinea-pigs.
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002217:Carbachol / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009928:Organ Specificity; D014132:Trachea / Q000187:drug effects*
D000318:Adrenergic beta-Agonists; D002217:Carbachol; D007545:Isoproterenol