Inhibition of the alpha--thrombin DFP catalytic portion does not incapacitate it physiologically: i. v. administration of such thrombin stimulates the second anticoagulating system. Aminasin abolishes this effect. These findings suggest that the thrombin preserves the portion of molecule responsible for reflex stimulation of the anticoagulating system. Microstructural changes of the apolar portion in different conditions deprives the alpha--thrombin to its ability to interact with the vascular bed's chemoreceptors. I. v. administration of such thrombin evoked no defense response in the organism.

Beta-thrombin possessing high esterase activity and tracing coagulating ability, being product of limited proteolysis of alpha-thrombin in vitro, accelerates recalcification time and thrombin generation in plasma, but not the conversion of prothrombin to enzyme. Thus, beta-thrombin is the activator of early stages of blood coagulation, does not possess fibrinolytic activity and does not activate plasminogen. The i. v. administration of beta-thrombin to rats induces changes in blood coagulability which are accompanied by an increase in plasma recalcification time, total fibrinolytic activity and non-enzymatic fibrinolysis. Nothing of the kind occurs after administration alpha-thrombin, having tracing clotting activity similar to R-thrombin activity. The data obtained suggest the possibility of reflex activation of the anticoagulating system by beta-thrombin or undirectly by alpha-thrombin generated by beta-thrombin activation at early stages of blood coagulation.

Formation of complex between heparin and prothrombin was shown using a spectral method. A method is developed for production of active complex heparin-prothrombin with the ratio of components as 1 : 6. The heparin-prothrombin complex obtained exhibited the anticoagulant and antipolymerization properties as well as the nonenzymatic fibrinolytic effect on instabilized fibrin both in absence and in presence of such blocking agents of enzymatic fibrinolysis as epsilon-aminocapronic acid and soybean inhibitor of trypsin. The increase in the anticoagulant and nonenzymatic fibrinolytic properties of blood occurred after intravenous administration of the complex into animals. The heparin-prothrombin complex acted in circulation within 1.5--2 hrs.

Injection of the intermediate 1 of prothrombin proteolysis into the frog's systemic circulation mobilized the anticoagulating and the fibrinolytic potential of the organism. This is not so in frogs with destroyed c.n. s. Electrical activity of the carotid chemoreceptors in considerably higher after perfusion with intermediate 1 of the frog's humorally isolated carotid labyrinth, as well as the total coagulation time, the total fibrinolytic activity, and the non-fermentative fibrinolysis in the systematic circulation. The data obtained suggest that the reflex activation of the physiological anticoagulating system can be induced can be induced by intermediate 1 which has the structure similar to thrombin but no clotting activity.

Two components - the intermediate product 1 (P-1) converting under certain conditions into thrombin, and product 2 (P-2) which possesses no such properties were isolated from the products of prothrombin proteolysis by thrombin. The intravenous injection of the P-1 to rats lengthened the blood coagulation time and plasma recalcification. The sum total fibrinolytic activity proved to increase and the fibrinogen concentration - to decrease. A sharp 5-fold rise of the nonfermentative fibrinolysis was observed. It seems that this effect of the anticoagulating and fibrinolytic potential mobilization was stimulated by the response of the second anticoagulating blood system.