Participation of blood cells in exercise-induced fibrinolysis

The fibrinolytic response to maximal exercise on a bicycle ergometer was studied in 42 normal young adults (21 males, 21 females) by euglobulin lysis and by 125I-fibrin radiometric assay of whole blood and plasma fibrinolytic activities. Increases in plasma activity by 125I-fibrin assay were similar (mean increase, 3- to 4-fold) to those observed by euglobulin lysis, and were inhibited (90-93% inhibition) by tranexamic acid at a concentration (10 mmol/l) which inhibits plasmin-mediated fibrinolysis. In addition, there was a considerable increment in the cellular phase component, evident from simultaneous 125I-fibrin assay of whole blood and plasma activities. This cellular increment occurred in 70% of subjects (16 of 21 males, and 13 of 21 females). It represented, on average, 73% of the activity increase induced in plasma by exercise, and was not inhibited by tranexamic acid. Counts of all blood cell types were increased with exercise, but there was no correlation between absolute values for or increments in counts of any cell type and the increments in cellular activity. Thus, the fibrinolytic response to exercise in the majority of normal individuals includes not only the well-known plasmin-mediated increase in plasma, which is inhibitable by tranexamic acid, but also a similar increment in cell-mediated activity, which is due to qualitative functional rather than quantitative changes in one or more as yet unidentified cell types, acting alone or in conjunction with plasma factors which are not inhibited by tranexamic acid.