[Turbidimetric analysis of fibrin polymerization in the plasma]

The turbidimetrical assay of thrombin-induced plasma coagulation provides a possibility to estimate both stages of fibrinogen-fibrin conversion. The initial one, which proceeds without any change of turbidity, reflects the process of protofibril formation, and the second stage of lateral aggregation, is characterized by the rise of turbidity. The influence of heparin, alga (Laminaria digitata) aqueons extracts, and collagenase on the indices of the turbidity-time curve has been studied. It was established that the alga extracts possessed the powerful heparin-like anticoagulant activity. The both agents influenced the first stage of the turbidity-time curve, suppressing protofibril formation, which reflects the thrombin inhibition. Nevertheless, they differed in their mode of dose-dependence. While the time of protofibril formation was direct proportional to the alga extract concentration, it was rising more intensively with heparin dose elevation. Plasma pre incubation with alga extract or heparin did not influence their action. Treatment with plasma collagenase changed only the second stage of the coagulation curve. It inhibited the process of protofibril lateral aggregation in the direct proportional manner. It must be due to fibrin digestion by the enzyme. We propose that fibrin cleavage by collagenase occurred out of the thrombin action sites, because the velocity of protofibril accumulation stayed unchanged. Our data illustrate the usefulness of the turbidimetrical analysis in the studies of the agents' action mechanisms on blood coagulation, in conditions close to physiological ones.