STUDIES OF THE PROTHROMBIN ACTIVATION PATHWAY UTILIZING RADIOIMMUNOASSAYS FOR THE F2/F1+2 FRAGMENT AND THROMBIN-ANTITHROMBIN COMPLEX

Abstract

The efficacy of using radioimmunoassays (RIA) for [human] prothrombin activation fragments (F2/F1+2) and for thrombin-antithrombin complex (TAT) in purified systems and in whole blood was evaluated. During venipuncture, appropriate anticoagulants were employed to prevent the generation of thrombin and factor Xa. The RIA were specific for F2/F1+2 and TAT and did not interact with other plasma components. Initially, thrombin generation was studied in a purified human system of prothrombin, antithrombin, factor Xa and factor V as well as phospholipid and Ca2+. Under these conditions, the kinetics of F2/F1+2 and TAT generation were virtually superimposable. When factor V was omitted from the reaction mixture, a significantly greater amount of F2/F1+2 as compared to TAT was observable. Prothrombin activation was monitored during the spontaneous coagulation of freshly drawn blood. Throughout the entire course of thrombin generation, the observable rate of formation of F2/F1+2 was considerably greater than that of TAT. The levels of F2/F1+2 and TAT in normal individuals were examined. The concentrations of F1+2 and TAT average 1.97 and 2.32 nM, respectively. The concentrations of F2/F1+2 and TAT in patients with disseminated intravascular coagulation were quantitated in these individuals, the levels of both components are elevated. The ratio of F1+2 to TAT ranges from 2.37 to 5.55. Under in vivo conditions, prothrombin activation is characterized by the accumulation of a stable precursor, such as prethrombin-2, and this phenomenon may be related to an alteration of factor V function.