Effect of twenty minutes of aerobic exercise on in vivo platelet release in moderately trained females: radioimmunoassay of platelet factor 4 and beta-thromboglobulin

Circulating blood platelets serve an important role in the physiological process of hemostasis. Physical exercise has been documented to result in alterations in many hemostatic parameters including platelet size, number and function. Most published research data support the hypotheses that both hemostasis and fibrinolysis become activated as a consequence of various levels of physical exercise. The purpose of this study was to determine the effect of twenty minutes aerobic exercise on platelet activation in vivo. Platelet activation in vivo is associated with the release of platelet granular contents. Platelet alpha granules contain two platelet specific proteins: platelet factor 4 (PF4) and beta-thromboglobulin (BTG). Elevated plasma levels of these proteins are a specific marker of in vivo platelet activation. Subjects were moderately trained female volunteers between the ages of 22 and 40 years. Subjects were exercised or twenty minutes on a bicycle ergometer at workloads that represented 65 to 75% of their functional capacity. Blood specimens were drawn within five minutes of exercise. Plasma samples from exercise and control subjects were assayed for PF4 and BTG using a sensitive competitive-binding radioimmunoassay procedure. The mean plasma levels of both proteins were significantly greater in the exercising subjects when compared with the non-exercising controls. Data from this study support the following research hypotheses: BTG plasma levels will be significantly higher in exercising subjects than in non-exercising controls, and PF4 plasma levels will be significantly higher in exercising subjects than in non-exercising controls