Comparison of platelet function during exercise in normal subjects and coronary artery disease patients: Potential role of platelet activation in myocardial ischemia

Platelet function parameters as influenced by exercise stress were evaluated in 22 patients with coronary artery disease (CAD) and in 13 normal subjects. Upon exercise stress, 14 CAD patients exhibited positive tests and eight exhibited negative tests. Platelet counts during exercise increased similarly in normal and CAD patients. Platelet aggregation response to ADP was unaffected by exercise both in normal and CAD patients. Platelets from 7 of the 14 CAD patients with positive stress tests had increased sensitivity to endoperoxide analog (U-46619) defined as less than 200 ng/ml U-46619 required for 50% platelet aggregation. Resting plasma beta-thromboglobulin (B-TG) levels, an index of in vivo platelet activation, were significantly higher in CAD patients compared to normal subjects (74 +/- 7 and 41 +/- 5 ng/ml, respectively; p less than 0.02). During exercise plasma B-TG levels increased in normal subjects to 60 +/- 5 ng/ml. In contrast, B-TG levels increased to 102 +/- 14 ng/ml in CAD patients (p less than 0.01 compared to normal subjects). These increases were transient and B-TG declined to preexercise values soon after exercise. Eleven of the 12 CAD patients with positive exercise stress tests had increases in plasma B-TG levels, whereas only three of the eight CAD patients with negative stress tests had any increase. These observations of increased platelet activation in certain CAD patients during exercise may be related to exercise-induced myocardial ischemia.