Relationship of platelet serotonin to disturbances of clotting and hemostasis

The presence of serotonin (5-hydroxytryptamine) in high concentration in platelets and its absence from normal platelet-free plasma suggest the possibility that this vasoconstrictor substance may play a role in hemostatic mechanisms. Platelet serotonin content measured by a fluorometric method in 94 patients showed an average content of 0.22 µg./ml. blood. In none of the disease groups studied, including hypertension, was a significant alteration found in platelet serotonin. However, the administration of reserpine resulted in a marked and prolonged depletion of platelet serotonin that was not accompanied by any significant change in any of the clotting factors. The in vitro addition of serotonin in amounts up to 50 µg./ml. also failed to alter any of the clotting factors studied. Platelet serotonin did not correlate with diagnosis, age, weight, blood pressure, cephalin-fluocculation, or capillary fragility. However, markedly anemic patients (below 10 Gm. per cent hemoglobin) and patients whose blood urea nitrogen was above 30 mg. per cent, tended to have a low platelet serotonin content.