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Flow Regulates Thrombin Generation Kinetics

Shear stress plays important roles in platelet coagulation. However, in many studies, coagulation rate constants were determined under static conditions. In the present study, we aimed to determine how flow affects thrombin generation rates, when coagulation factors were immediately available. Washed platelets were exposed to various dynamic shear stress (physiological and pathological) in a cone and plate shearing device, with Factor Xa, prothrombin, and calcium. Thrombin generation was quantified using chromozym‐TH absorbance at 405 nm. Platelet activation was assessed by cell surface P‐selectin expression using flow cytometry. The results demonstrate that elevated dynamic shear stress induced a significant increase in P‐selectin expression, indicating platelet activation. However, thrombin generation rate was significantly reduced under elevated shear stress, compared to that under low or physiological shear stress. Such results were different from that observed with a prothrombinase assay following platelet exposure to dynamic shear stress. The immediate availability of coagulation factors likely contributed to the observed differences. These data suggest that dynamic shear stress affects thrombin generation kinetics, not only by affecting platelet activation state, but also by affecting prothrombinase complex formation on platelet surface. Thrombin generation rates could be reduced under accelerated flow and elevated shear stress, as reaction time for prothrombinase complex to form is significantly reduced.