Studies on the Thrombolytic Activity of Human

The process of in vivo clot dissolution, termed thrombolysis,l is complex, involving the interaction of clot components with the surrounding plasma. Participating in this interaction are plasminogen, plasminogen activator, plasmin, the plasmin inhibitory activity of plasma, and fibrin (1). Although much is known of the nature and quantities of individual components, the complexity of the thrombolytic process has led to difficulty in assessment of the overall capability of the plasma for effecting clot lysis under physiological conditionsan activity hereafter termed plasma thrombolytic activity. Plasma thrombolytic activity is a property of major physiological significance (2, 3) but hitherto the technical methods used for its assay have been imperfect. Assays involving determination of whole blood or plasma clot lysis time are valuable for detecting markedly enhanced thrombolysis but are inadequate for measurement of low levels of thrombolytic activity due to the very long lysis times found and the lack of a precise endpoint. Other assays have involved physicochemical alterations of the plasma such as dilution (4, 5), isolation of the euglobulin fraction (6, 7) and extraction with organic solvents (8). Such physicochemical procedures isolate or affect to a variable degree one or more components of the thrombolytic process and, although valuable for specialized purposes, disturb the complex balance between the individual plasma components (1). Consequently, assays of this nature are unsuitable for other than qualitative determination of plasma thrombolytic activity.