PLATELET AGGREGABILITY IN-VIVO IS ATTENUATED BY VERAPAMIL BUT NOT BY METOPROLOL IN PATIENT WITH STABLE ANGINA-PECTORIS

The effects of 1 month of treatment with either verapamil or metoprolo l on several aspects of platelet function were studied at rest and dur ing physical exercise or mental stress in patients with stable angina pectoris participating in the Angina Prognosis Study in Stockholm. Pla telet aggregability was measured by filtragometry ex vivo, which refle cts platelet aggregability in vivo and by Born aggregometry in vitro, Platelet secretion in vivo was assessed by measurements of beta-thromb oglobulin in plasma. Verapamil reduced plasma norepinephrine levels (f rom 2.6 +/- 1.0 to 2.2 +/- 1.0 nmol/L; p <0.01) and attenuated platele t aggregability at rest (filtragometry readings were prolonged from 21 9 to 295 seconds; p <0.05, n = 46). Aggregability in platelet-rich pla sma was not influenced. Metroprolol did not significantly affect filtr agometry readings (n = 58) or aggregability in vitro (there was a tend ency toward enhanced adenosine diphosphate sensitivity; p = 0.08), bet a-thromboglobulin levels were low (approximate to 25 ng/ml) and not in fluenced by either treatment. Physical exercise (bicycle ergometry) in creased platelet aggregability in vivo both before and after drug trea tment. Verapamil also attenuated platelet aggregability after exercise , whereas metoprolol had no such effect, Platelet function was not ser iously altered mental stress (Stroop's color word test) despite effect s on hemodynamics and plasma either before or after treatment with eit her drug, Thus, verapamil attenuates platelet aggregability in patient s with stable angina pectoris, whereas metoprolol has no such effect.