Thrombomodulin activity in commercial thromboplastin preparations
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Recently, it was reported that endothelial cells contain a membrane protein which serves as a cofactor for the activation of protein C by thrombin (thrombomodulin). Because many commercial thromboplastins are prepared from vessel-rich tissues/organs (lung, brain, placenta), it was hypothesized that some preparations may contain significant amounts of thrombomodulin; theoretically, thrombomodulin contaminations may enhance the prothrombin time. Among 8 different commercial thromboplastins tested two thromboplastins were found to contain significant amounts of thrombomodulin activity: Simplastin (64 U/ml) and Ortho (12.8 U/ml). However, we were unable to demonstrate that the presence of the thrombomodulin activity in these thromboplastins could affect the prothrombin time either by delaying fibrin formation (formation of thrombin-thrombomodulin complexes) or by inhibiting activated factor V (formation of activated protein C).
Recently, it was reported that endothelial cells contain a membrane protein which serves as a cofactor for the activation of protein C by thrombin (thrombomodulin). Because many commercial thromboplastins are prepared from vessel-rich tissues/organs (lung, brain, placenta), it was hypothesized that some preparations may contain significant amounts of thrombomodulin; theoretically, thrombomodulin contaminations may enhance the prothrombin time. Among 8 different commercial thromboplastins tested two thromboplastins were found to contain significant amounts of thrombomodulin activity: Simplastin (64 U/ml) and Ortho (12.8 U/ml). However, we were unable to demonstrate that the presence of the thrombomodulin activity in these thromboplastins could affect the prothrombin time either by delaying fibrin formation (formation of thrombin-thrombomodulin complexes) or by inhibiting activated factor V (formation of activated protein C).