In this paper we tested a group of 66 healthy volunteers in terms of the influence of circadian rhythm on selected parameters of the coagulation system and fibrinolytic system. Blood was collected at 6-hour intervals, at 8 am, 2 pm, 8 pm and 2 am. Circadian variability was observed in the coagulation system parameters as well as in the fibrinolytic system. We observed increased platelet aggregation, APTT prolongation, along with increased levels of factors (fibrinogen, PAI-1) and PAP and TAT complexes that influence coagulation and fibrinolysis systems, in the blood samples collected in the morning (8 am). We also demonstrated a circadian rhythm in the number of circulating platelets (PLT), with a peak in the afternoon (2 pm) accompanied by increased concentrations of t-PA, D-dimers and PT prolongation. Based on the obtained results it was possible to conclude that circadian rhythm had an influence on the activation of coagulation processes in the morning, with a progressive activation of fibrinolysis up to the afternoon. Our results may be helpful in determining the transient risk of cardiovascular events, including myocardial infarction and ischemic stroke, and hence, can contribute to the effective prevention of such events. Such observations may also become a starting point of departure for further studies aimed at determining the circadian effect of secretion of parameters in the hemostasis system on the other systems and parameters in the human body.
Keywords: Circadian rhythm; Coagulation; Fibrinolysis; Hemostasis; Platelet aggregation.
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