Role of Serotonin in Blood Coagulation

¹ From the U. S. Naval Radiological Defense Laboratory, San Francisco, California

Effects of serotonin (₅HTA) were studied a) in whole blood (in vitro) from both normal and x-irradiated animal, and b) in isolated clotting systems of plasma and purified fibrinogen. ₅HTA was found to play an active role in blood coagulation in addition to its previously demonstrated role as a vasoconstrictor. In whole blood from normal and irradiated animals, and in platelet-deficient plasma, ₅HTA acts in a manner similar to platelet factor 2 in accelerating the conversion of fibrinogen to fibrin. In a purified fibrinogen solution, ₅HTA inhibits the fibrinogen-fibrin reaction, and thus differs from platelet factor 2. This may be due to the absence of an antithrombin in the purified fibrinogen solution. Serotonin appears to have a therapeutic effect on the postirradiation coagulation defect in that it decreases the prolonged heparin clotting time. This increased sensitivity to heparin during the postirradiation thrombocytopenia may be due to a deficiency of serotonin, which acts as an antagonist to heparin (an antithrombin). The action of ₅HTA is postulated as an antagonist of an antithrombin which blocks the fibrinogen to fibrin reaction.

Note:
with the technical assistance of R. D. Pate