Positive inotropic effects of the beta 2-adrenoceptor agonist terbutaline in the human heart: effects of long-term beta 1-adrenoceptor antagonist treatment.
OBJECTIVE
This study was conducted to determine whether activation of cardiac beta 2-adrenoceptors increases contractility in humans and whether this is affected by long-term beta 1-adrenoceptor antagonist treatment.


BACKGROUND
Coexistence of beta 1- and beta 2-adrenoceptors in the human heart is generally accepted. The functional importance of cardiac beta 2-adrenoceptors for increases in contractility in humans, however, has not been completely established.


METHODS
We studied 1) the beta-adrenoceptor subtype mediating positive inotropic effects of the beta 2-adrenoceptor agonist terbutaline in vitro (on right atrial and left ventricular preparations from nonfailing human hearts) and increases in contractility (by measurement of systolic time intervals) in vivo in seven healthy male volunteers; and 2) in vivo whether long-term treatment of volunteers with the beta 1-adrenoceptor antagonist bisoprolol affects terbutaline-induced increases in contractility.


RESULTS
In vitro terbutaline caused a concentration-dependent increase in atrial and ventricular adenylate cyclase activity and force of contraction. Terbutaline effects were antagonized only by the beta 2-adrenoceptor antagonist ICI 118,551, indicating that they were mediated by beta 2-adrenoceptor stimulation. In vivo intravenous infusions of terbutaline (dose range 25 to 300 ng/kg body weight per min for 15 min) dose dependently increased heart rate and shortened the pre-ejection period and heart rate-corrected electromechanical systole (QS2) time. These effects are mediated predominantly by beta 2-adrenoceptor stimulation because they were only marginally affected by the beta 1-adrenoceptor antagonist bisoprolol (1 x 10 mg orally), either given 2 h before infusion or long term for 3 weeks.


CONCLUSIONS
Stimulation of cardiac beta 2-adrenoceptors in humans causes not only in vitro but also in vivo positive inotropic effects. Long-term beta 1-adrenoceptor antagonist treatment does not considerably affect beta 2-adrenoceptor-mediated in vivo increases in contractility. Thus, it may be possible to treat patients with chronic heart failure and long-term beta 1-adrenoceptor antagonist therapy with beta 2-adrenoceptor agonists if immediate inotropic support is needed.
Schäfers
R F
RF
Department of Internal Medicine, University of Essen, Germany.
Adler
S
S
Daul
A
A
Zeitler
G
G
Vogelsang
M
M
Zerkowski
H R
HR
Brodde
O E
OE
D000262:Adenylyl Cyclases / Q000187:drug effects / Q000378:metabolism; D000328:Adult; D017298:Bisoprolol / Q000008:administration & dosage / Q000494:pharmacology*; D002316:Cardiotonic Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006321:Heart / Q000187:drug effects*; D006325:Heart Atria / Q000187:drug effects / Q000201:enzymology; D006339:Heart Rate / Q000187:drug effects; D006352:Heart Ventricles / Q000187:drug effects / Q000201:enzymology; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D013599:Systole / Q000187:drug effects; D013726:Terbutaline / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D002316:Cardiotonic Agents; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D013726:Terbutaline; D017298:Bisoprolol