Assessment of two in vitro methods for determination of the apparent affinities of beta-sympathomimetics on myocardial contractility

Offermeier, J.; Smit, E.S.; Dreyer, A.C.

Journal of Pharmacy and Pharmacology 28(10): 787-788


ISSN/ISBN: 0022-3573
PMID: 10380
DOI: 10.1111/j.2042-7158.1976.tb04053.x
Accession: 068517885

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To determine to what extent contraction frequency influences the apparent affinities of .beta.-sympathomimetic drugs for the inotropic receptors, changes were recorded in the force of contraction induced by different .beta.-sympathomimetic drugs [isoprenaline, salbutamol, dobutamine] employing spontaneously beating guinea pig atrial preparations (heart frequency 105 .+-. 10) and left atrial strips which were electrically stimulated at 1 s intervals. Comparison of the pD2 [negative logarithm of the molar concentration of ED50] values obtained by these 2 different methods, indicated that the relative apparent affinities for all 3 drugs tested were notably higher in the case of the spontaneously beating atria frequency of contraction which potentiated the force of contraction. Changes in frequency of contraction do influence apparent affinity values for the inotropic receptors for .beta.-adrenergic agonists to varying degrees.