Effects of atropine on human cardiac beta 1- and/or beta 2-adrenoceptor stimulation.
The aim of this study was to find out whether, in humans, the increase in vagal tone accompanying cardiac beta-adrenoceptor (beta-AR) stimulation might be different dependent on beta1- or beta2-AR stimulation. For this purpose we studied, in six male healthy volunteers (aged 28+/-1 years), the effects of atropine infusion (0.15 microg/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 beta1-and beta2-AR), terbutaline (25-150 ng/kg/min, increasing HR and QS2c via beta2-AR), adrenaline (20-160 ng/kg/min, increasing HR via beta2-and QS2c via beta1-AR) and bicycle exercise in supine position (increasing HR and QS2c via beta1-AR). The three beta-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 beta-AR agonists and exercise; increases were larger for beta2-AR (terbutaline, adrenaline) mediated effects than for beta1-AR (exercise) mediated effects. Moreover, atropine enhanced beta-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, beta1-and beta2-AR mediated stimulation evoked HR-increases are composed of two components: increases via direct beta-AR stimulation and simultaneously decreases via increase in vagal tone. In addition, beta-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.
Bruck
Heike
H
Institute of Pharmacology, University of Halle, 06096 Halle, Germany.
Ulrich
Anke
A
Gerlach
Stefan
S
Radke
Joachim
J
Brodde
Otto-Erich
OE
D058665:Adrenergic beta-1 Receptor Agonists; D058666:Adrenergic beta-2 Receptor Agonists; D000328:Adult; D000704:Analysis of Variance; D001285:Atropine / Q000494:pharmacology*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008297:Male; D018342:Receptors, Adrenergic, beta-1 / Q000502:physiology; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology
D058665:Adrenergic beta-1 Receptor Agonists; D058666:Adrenergic beta-2 Receptor Agonists; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D001285:Atropine; D004837:Epinephrine