Non-catechol phenylethanolamines: agonistic and antagonistic actions on beta-adrenoreceptors in isolated tissues from the guinea-pig.

Abstract

SUMMARY 1. Agonistic and antagonistic activities on β-adrenoreceptors have been assessed for orciprenaline, terbutaline, soterenol and MJ7999–1 using isolated guinea-pig atrial (β1-receptor) and tracheal (β2-receptor) preparations. 2. As agonists MJ7999–1 is more selective for β2-receptors than soterenol because of its increased activity in trachea, whereas terbutaline is more selective for β2-receptors than orciprenaline because of its decreased activity in atrial preparations. 3. Antagonistic activity was assessed from shifts in concentration-effect curves to (-)-isoprenaline. 4. MJ7999–1 and soterenol possess competitive β-receptor blocking actions in atrial (pA2≈6.5) and tracheal (pA2≈6.0) preparations. 5. Orciprenaline and terbutaline are relatively selective competitive β-receptor antagonists, being more potent in atrial (pA2≈6.3) than in tracheal (pA2∼4.9) preparations. In atria non-competitive antagonistic actions are apparent with these two drugs. 6. In rat vas deferens preparations only (-)-isoprenaline and soterenol display agonistic actions on α-receptors. None of the compounds possesses α-receptor antagonistic activity.