Effect of beta-blockers on free radical-induced cardiac contractile dysfunction

We examined the effects of hydroxyl radicals (OH.) on human myocardial contractility and on sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) activity and the effects of the beta-receptor antagonists metoprolol, carvedilol, and its metabolite BM-910228.

Isometric force of contraction was determined in isolated human myocardium. H(2)O(2) 1 mmol/L and Fe(3+)-nitrilotriacetic acid (Fe(3+)-NTA) 0.1 mmol/L used for generation of OH. induced a decrease in basal force of contraction and an increase in diastolic tension in atrial and left ventricular myocardial preparations. After challenge with OH., the maximum positive inotropic response to Ca(2+) 1.8 to 15 mmol/L was decreased by 60% and by 39%, respectively. The effects of OH. could be blocked by catalase. Carvedilol and its metabolite BM-910228 attenuated the OH.-induced impairment of the inotropic response to Ca(2+) in atrial myocardial preparations. Metoprolol had no significant effect. The stimulation frequency (0.5 to 3.0 Hz)-dependent increase in force of contraction and decrease in diastolic tension were abolished after exposure of atrial trabeculae to OH. In parallel, SERCA activity was decreased by OH. concentration-dependently, as determined in myocardial membrane preparations. BM-910228 partially restored the force-frequency relationship and preserved SERCA activity.

OH. radicals induce an impairment of contraction and relaxation and an attenuation of the force-frequency relationship in human myocardium accompanied by an inhibition of SERCA. Carvedilol and BM-910228 partly prevented OH.-induced contractile dysfunction. These observations could explain the improvement of ejection fraction in heart failure trials with carvedilol without a restoration of beta-adrenergic receptor density.