Release of pro-coagulant microparticles after moderate endurance exercise

To the editor, Elevated plasma concentrations of cell-membranederived microparticles (MP) are found in many diseases such as sepsis, cancer, and diabetes mellitus [1, 2]. Various cell types are known as sources of MP, which play a crucial role in angiogenesis, endothelial cell function as well as coagulation and inflammation. A uniform characteristic of the various cell-specific MP is the surface exposure of negatively charged phospholipids. Due to these phospholipids and also due to the exposure of tissue factor (TF) and/or TF pathway inhibitor, MP are believed to be involved in the regulation of coagulation [3, 4]. Furthermore, MP bear cell-specific antigens enabling them to interact with a variety of target cells. Thus, MP can be considered as intercellular signal transferring entities [5, 6]. Low levels of circulating MP, mainly derived from platelets, are also present in healthy individuals but their functional relevance in haemostasis and inflammation is not well understood [7]. Increased levels of circulating MP are known to be associated with an increased risk of cardiovascular disease and atherothrombotic events [1, 8]. Since moderate physical exercise is known to lower the risk of cardiovascular diseases [9, 10], we were interested to study the effect of moderate physical exercise on both concentration and pro-coagulant activity of circulating MP. After approval by the local Ethics Committee and obtaining written informed consent, 16 healthy male volunteers (age 25 3 years; mean SD) underwent a singular 90 min exercise test on a bicycle ergometer with a constant power of 80% of individual anaerobic threshold (IAT). IAT was determined one week prior to the test according to Stegmann et al. [11]. Blood samples were taken before (rest), immediately post (post) and 45 min (45 min post) as well as 2 hours (2 h post) after exercise. MP were identified by flow cytometry according to their size and the binding of FITC-labelled annexin V as well as by the binding of PE-labelled antibodies against cell-specific antigens: platelet-derived MP (PMP) by anti-CD42a, monocyte-derived MP (MMP) by anti-CD14 and endothelial cell-derived MP (EMP) by anti-CD62E. To estimate procoagulant activities of MP two different tests were performed: The ACTICHROME test (American Diagnostica), which measures the pro-thrombinase activity of FXa/Va of MP bound to an annexin V-coated surface in absence of any other plasma constituents and a one-stage clotting test, in which the formation of a fibrin clot was monitored by measuring the optical density in MP-containing plasma samples after re-calcification and addition of a small amount of TF. The 90 min exercise at 80% IAT (mean power 173 73 W) increased heart rate to 156 16 beats/ min, the systolic blood pressure to 156 25 mm Hg and plasma lactate concentration to 2.17 0.81 mmoles/l. As shown in Table I, the exercise resulted in a significant increase in the numbers of white blood cells and platelets. It has been shown elsewhere that the increase in platelet and leukocyte counts is not only due to a reduction in plasma volume but also due to a release of platelets and leukocytes from various storage sites (spleen, lung, bone marrow etc.) [9]. With respect to MP, we also