Activation of haemostasis by exercise, mental stress and adrenaline: effects on platelet sensitivity to thrombin and thrombin generation

Stress-induced activation of haemostasis may be involved in the triggering of acute coronary syndromes. We compared the effects of mental stress, dynamic exercise and adrenaline infusion on platelet sensitivity to thrombin using flow-cytometric analysis of platelet fibrinogen binding in whole blood, and platelet aggregability using filtragometry ex vivo, in healthy volunteers. Furthermore, we assessed thrombin generation [prothrombin fragment 1­2 (F1+­2) and thrombin-antithrombin complexes in plasma] and thrombin activity (fibrinopeptide A in plasma). Exercise (bicycle ergometry) enhanced thrombin-induced platelet fibrinogen binding (P<0.05) and platelet aggregability (P<0.01), and elevated F1­+2, thrombin-antithrombin complexes and fibrinopeptide A (P<0.05 for all three). Adrenaline infusion enhanced thrombin-induced platelet fibrinogen binding and platelet aggregability (P<0.05), and elevated thrombin-antithrombin complexes (P<0.05), whereas F1+­2 and fibrinopeptide A levels were not significantly affected. Mental stress increased platelet sensitivity to high concentrations of thrombin only, and produced small increases in levels of thrombin-antithrombin complexes. Time control experiments showed no important changes with repeated measurements during rest. Platelet responses to exercise and adrenaline were reversible, with recovery 60 min later. Thus, heavy exercise and high levels of adrenaline reversibly increased platelet aggregability and platelet sensitivity to thrombin, and enhanced thrombin formation; the effects were most pronounced during exercise. Mental stress only weakly affected these parameters.