Beta 1-blockade and acute coronary ischemia. Possible role of platelets.

Abstract

Although the benefit of beta-adrenergic blocking agents in acute coronary ischemia has been well documented, it is unclear whether the responsible mechanisms include the modification of platelet function. In recent studies, metoprolol appeared to reduce the total number and duration of episodes of silent ischemia in patients with stable coronary artery disease throughout the day. This effect was not associated with a change in baseline or circadian variability of the platelet aggregability. Since the treatment caused significant decreases in heart rate and blood pressure, the drug effect is more likely to be based on reduction of myocardial oxygen demand. Metoprolol, however, prevented a platelet aggregability increase and intracellular cAMP decrease during exercise stress testing in patients with stable angina pectoris. We speculate that this effect of beta 1-adrenergic blockade may be due to hemodynamic and neurohormonal changes, or possibly also to an increase in synthesis or release of platelet inhibiting substances.