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- Title
Effects of atropine on human cardiac β<sub>1</sub>- and/ or β<sub>2</sub>-adrenoceptor stimulation.
- Authors
Bruck, Heike; Ulrich, Anke; Gerlach, Stefan; Radke, Joachim; Brodde, Otto-Erich
- Abstract
The aim of this study was to find out whether, in humans, the increase in vagal tone accompanying cardiac β-adrenoceptor (β-AR) stimulation might be different dependent on β1- or β2-AR stimulation. For this purpose we studied, in six male healthy volunteers (aged 28±1 years), the effects of atropine infusion (0.15 μg/kg/min continuously) on increase in heart rate (HR) and contractility (determined as shortening of HR-corrected duration of electromechanical systole-QS2c) evoked by infusion of isoprenaline (3.5–35 ng/kg/min, increasing HR and QS2c via β1-and β2-AR), terbutaline (25–150 ng/kg/min, increasing HR and QS2c via β2-AR), adrenaline (20–160 ng/kg/min, increasing HR via β2- and QS2c via β1-AR) and bicycle exercise in supine position (increasing HR and QS2c via β1-AR). The three β-AR agonists and exercise increased HR and shortened QS2c in a dose- or work-load-dependent manner, respectively. Atropine enhanced HR-increasing effects of all three β-AR agonists and exercise; increases were larger for β2-AR (terbutaline, adrenaline) mediated effects than for β1-AR (exercise) mediated effects. Moreover, atropine enhanced β-AR agonists-induced QS2c shortening; however, atropine effects on QS2c were markedly less pronounced than on HR. From the results we conclude that, in humans, β1-and β2-AR mediated stimulation evoked HR-increases are composed of two components: increases via direct β-AR stimulation and simultaneously decreases via increase in vagal tone. In addition, β-AR mediated increases in contractility are also dampened by simultaneous activation of vagal tone but to a lesser extent possibly because human ventricular myocardium is only sparsely parasympathetically innervated.
- Subjects
ATROPINE; ADRENERGIC receptors; HEART beat; CARDIAC contraction; CONTRACTILITY (Biology); SUPINE position
- Publication
Naunyn-Schmiedeberg's Archives of Pharmacology, 2003, Vol 367, Issue 6, p572
- ISSN
0028-1298
- Publication type
Article
- DOI
10.1007/s00210-003-0757-9