Role of serotonin in blood coagulation.

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 hepari...