Decrease of prothrombin level during thrombolysis in acute myocardium infarction.

Previously, the direct interactions of Bβ26-42 fibrin residues with prothrombin were demonstrated. It was also shown that forming prothrombin complexes with E- or DDE-fragments causes non-enzymatic prothrombin activation. The direct measuring of the prothrombin level in the blood plasma of patients with acute myocardial infarction (AMI) allowed us to find a situation where such an activation can occur in vivo. Blood coagulation parameters in the blood plasma of patients with AMI were measured at 2 hours, three days, and seven days after the thrombolysis by streptokinase accompanied with intravenous administration of anticoagulants: unfractionated high molecular weight heparin (HMWH) and low-molecular-weight heparin (LMWH). The prothrombin level in the blood plasma of patients with AMI was normal before thrombolytic therapy and substantially decreased after streptokinase administration. This effect was prominent in the case of concomitant anticoagulant therapy with LMWH and was not observed when HMWH was applied. It can be explained by the fact that LMWH preferentially inhibits factor Xa, while the HMWH is an effective inhibitor of both factor Xa and thrombin. This observation suggested that the prothrombin level decrease was caused by the thrombin-like activity and possible autolysis of prothrombin by thrombin. Also, thrombolytic therapy with streptokinase caused the accumulation of fibrin degradation products (FDPs), some of which were able to bind prothrombin. The dramatic decrease of prothrombin level in the blood plasma of patients with AMI during thrombolysis allowed us to conclude the non-enzymatic prothrombin activation with the following autolysis of prothrombin that contributes to the pathology.