Differentiation of cardiac chronotropic and inotropic effects of beta-adrenoceptor agonists.
The relative inotropic and chronotropic activity of beta-adrenoceptor agonists was studied in the noradrenaline-depleted, anaesthetized cat. Terbutaline, a selective beta2-adrenoceptor agonist, gave at a certain dose a more pronounced chronotropic than inotropic response, while a new beta1-selective adrenoceptor agonist (-)-H 80/62 produced the same degree of chronotropic and inotropic stimulation. The results indicate that there is some difference between the beta-adrenoceptors in the sinus node mediating chronotropic stimulation and beta-adrenoceptors in the ventricular myocardium mediating stimulation of the contractile force. It has been shown that there are both beta1- and beta2-adrenoceptors in the heart (Carlsson et al., 1972). In the light of this finding it is hypothetized that there are differences in the relative distribution of beta1- and beta2-adrenoceptors in the sinus node and in the myocardium. Athough beta1 is the predominant type of beta-adrenoceptor in both regions, the beta1:beta2 concentration ratio seems to be higher in the myocardium, than in the sinus node.
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D011412:Propanolamines / Q000494:pharmacology; D013268:Stimulation, Chemical; D013726:Terbutaline / Q000494:pharmacology; D014665:Vasodilator Agents
D000318:Adrenergic beta-Agonists; D011412:Propanolamines; D014665:Vasodilator Agents; D007545:Isoproterenol; D013726:Terbutaline