Platelet-dependent thrombography gives a distinct pattern of in vitro thrombin generation after surgery with cardio-pulmonary bypass: potential implications.

BACKGROUND: Bleeding remains a potentially lethal complication of cardio-pulmonary bypass (CPB) surgery. The purpose of this study was to obtain a better insight into in vitro thrombin generation in the context of CPB. METHODS: We used Calibrated Automated Thrombography to assess blood coagulation of 10 low-risk patients operated for valve replacement with CPB, under 2 experimental conditions, one implicating platelets as platelet dysfunction has been described to occur during CPB. RESULTS: Our main finding was that CPB-induced coagulopathy was differently appreciated depending on the presence or absence of platelets: the decrease in thrombin generation was much less pronounced in their presence (mean endogenous thrombin potential change values before and after CPB were -3.9% in the presence of platelets and -39.6% in their absence). CONCLUSION: Our results show that experimental conditions have a profound effect in the study of in vitro thrombin generation in the context of CPB.

Cyclic stretch-induced thrombin generation by rat vascular smooth muscle cells is mediated by the integrin αvß3 pathway.

AIMS: Vascular smooth muscle cell (VSMC) phenotypic modulation plays a pivotal role in atherothrombotic diseases. Thrombin generation at the surface of VSMCs and activation of integrin mechanotransduction pathways represent potential mechanisms. Here, we examine whether mechanical stretch increases thrombin generation on cultured rat aortic VSMCs. METHODS AND RESULTS: The integrin α(v)ß(3) antagonist peptide (cRGDPV) dose-dependently decreased thrombin generation without stretch. Static stretch (5%, 1 Hz) failed to modify the thrombin-forming capacity of VSMCs, whereas 10% cyclic stretch during 60 and 360 min enhanced integrin α(v)ß(3) expression and thrombin generation at the surface of VSMCs by 30% without inducing apoptosis. Cyclic stretch also stimulated Src phosphorylation, cleavage of talin, and binding of prothrombin to VSMCs. Upregulation of α(v)ß(3) expression, Src phosphorylation, and enhanced thrombin generation by cyclic stretch were abolished by cRGDPV and silencing RNA (siRNA) against α(v) as well as by selective inhibition of integrin α(v)ß(3) inside-out signalling by a talin-siRNA. Complete abolition of stretch-induced VSMC-supported thrombin generation by the RGT peptide, which disrupts the interaction of Src with the ß(3) cytoplasmic tail, demonstrates the link between outside-in pathways involving ß(3)-Src interaction and thrombin activity dependent on inside-out signalling. CONCLUSION: These data show that the contribution of cyclic stretch to VSMC-supported thrombin generation is driven by the integrin α(v)ß(3) signalling pathway and suggest a role for pulsatility-induced intramural thrombin in VSMC-dependent vascular remodelling.