Increased blood fibrinolytic activity after aspirin ingestion.

Fibrinolytic activity of whole blood and of platelet-deficient plasma, measured by 125I-fibrin assay in four normal subjects before and after ingestion of 1.8 g of aspirin, increased 33 to 150 per cent at one to three hours, at plasma salicylate levels of 5 to 18 mg per 100 ml. In two, plasma activity also increased. Fibrinolysis in blood, but not in plasma, increased 66 per cent after sodium salicylate. Sodium salicylate increased fibrinolytic activities of blood and of purified polymorphonuclear leukocytes in vitro, whereas aspirin had little effect. These striking effects of aspirin on cellular and fluid phases of blood fibrinolysis are apparently distinct from known aspirin actions on platelets. Plasma fibrinolytic activity accounted for only 18.8 +/- 12.3 per cent (S.D.) and 17.4 +/- 10.4 per cent of the activity measured in the corresponding whole blood of 11 normal men and 10 normal women, respectively, indicating the importance of cellular elements in normal blood fibrinolysis.