Summary
The relative inotropic and chronotropic activity of β-adrenoceptor agonists was studied in the noradrenaline-depleted, anaesthetized cat. Terbutaline, a selective β 2-adrenoceptor agonist, gave at a certain dose a more pronounced chronotropic than inotropic response, while a new β 1-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 β-adrenoceptors in the sinus node mediating chronotropic stimulation and β-adrenoceptors in the ventricular myocardium mediating stimulation of the contractile force. It has been shown that there are both β 1- and β 2-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 β 1- and β 2-adrenoceptors in the sinus node and in the myocardium. Although β 1 is the predominant type of β-adrenoceptor in both regions, the β 1:β 2 concentration ratio seems to be higher in the myo-cardium, than in the sinus node.
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Carlsson, E., Dahlöf, CG., Hedberg, A. et al. Differentiation of cardiac chronotropic and inotropic effects of β-adrenoceptor agonists. Naunyn-Schmiedeberg's Arch. Pharmacol. 300, 101–105 (1977). https://doi.org/10.1007/BF00505039
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DOI: https://doi.org/10.1007/BF00505039