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.

Injection of Intermediate product I (P-I) resulting from prothrombin proteolysis by thrombin, into the systemic circulation of frog leads to mobilization of the anticoagulating and fibrinolytic potential of the organism. No effect is observed in animals with destroyed central nervous system. Perfusion of humorally isolated carotid labyrinth of frog by P-I considerably increases the bioelectric activity of carotid chemoreceptors and induces changes in blood coagulability in the systemic circulation. The resulting changes are accompanied by an increase in total coagulation time, overall fibrinolytic activity and non-enzymic fibrinolysis. The data obtained are indicative of reflex excitation of the anticoagulating system by P-I, which possesses no coagulating activity, but is structurally similar to thrombin.