Reversal of Abnormal Platelet Aggregability and Change in Exercise Tolerance in Patients with Angina Pectoris Following Oral Propranolol

Abstract

Nineteen patients with severe but stable angina pectoris who had positive ECG response to exercise on a bicycle ergometer and 11 normal subjects were studied. Patients received placebo for six weeks and were then randomized into placebo (n = 9) and propranolol (n = 10) treatment groups. Threshold for platelet aggregation in response to adenosine diphosphate (ADP) was measured in fresh platelet rich plasma. Mean concentration of ADP necessary for a biphasic threshold aggregation response was 1.56 µM (geometric mean) in patients and 3.85 µM in normals ( P < 0.01). Serial studies with placebo showed no significant change in ADP threshold. With propranolol, 80 mg/day, platelet aggregation in response to ADP was entirely normalized; 3.79 µM ADP produced maximal aggregation compared to 1.32 µM before therapy ( P < 0.01). No additional changes were noted with propranolol, 160 mg/day. In the propranolol-treated patients (80 mg/day) who demonstrated reduction in ADP-induced platelet aggregation, total work during exercise increased by 128%, from 765 ± 125 (standard error of mean) kpm during the control period to 1,- 792 ± 285 kpm ( P < 0.01). Thus patients with angina and abnormal exercise tolerance demonstrate increased platelet aggregability in vitro which is restored toward normal with propranolol in dosage sufficient to improve exercise tolerance.