P144	Heterogeneity of tissue-derived anticoagulant effects on plasma thrombin generation.
K.Frederix, R.van Oerle, D.Fens, K.Hamulyák, H.M.H.Spronk, H.ten Cate
Laboratory of clinical Thrombosis and Hemostasis, Department of Internal Medicine, Cardiovascular Research Institute Maastricht, University of Maastricht, Maastricht, NL.

The blood coagulation system serves a critical role in maintaining a balance between pro/ and anticoagulant forces. Reduced expression of anticoagulant molecules may under conditions of inflammation or atherosclerosis lead to intravascular fibrin formation or overt thrombosis. Besides alterations in major vessels, organs containing an extensive endothelium surface, provide a major pool of anticoagulant reserve. Tissue dependent heterogeneity in pro/ and anticoagulant forces may be relevant for thrombogenicity but the functional expression of its determinants is unknown. In order to investigate potential thrombogenic activity in tissue homogenates we established a method to determine the endogenous thrombin potential on mouse organs using the calibrated automated thrombogram (Thrombinoscopy, Maastricht, The Netherlands). Methods and Results: Addition of liver and brain homogenates had no influence on thrombin generation in normal human plasma (1847±38 nM/min). In contrast, the addition of lung, heart, or kidney homogenates caused a substantial inhibition of thrombin generation in human plasma. Kidney homogenates inhibited thrombin formation in human plasma up to 80% (1478±332 nM/min; n=3), whereas addition of heart and lung homogenates reduced thrombin formation to respectively 5% (86±20 nM/min) and 1% (14±25 nM/min). The tissue-derived anticoagulant effects on plasma thrombin generation were completely abolished in protein C-deficient plasma. No inhibition on thrombin generation was observed after the addition of any of the tissue homogenates derived from TM pro/pro animals. Kidney (2425±22 nM/min), heart (1625±468 nM/min), and lung (2000±175 nM/min) from TMpro/pro animals restored thrombin generation to respectively 131%, 88%, and 108% compared to homogenates from wild-type animals. Conclusions: Normal mouse tissues, except brain and liver, have a substantial anticoagulant effect in a thrombin generation assay. This anticoagulant effect appears to be due to tissue-derived thrombomodulin, mediating the activation of plasma protein C. Murine lung and heart contain most thrombomodulin activity, whereas kidney posses moderate levels. In conclusion, the calibrated automated thrombogram method is a powerful tool for determination of altered anticoagulant reserve of different organs in pathophysiological conditions.

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