Enhancement of vitreous clot lysis by urokinase: mode of action.

Abstract The roles of fibrinolytic mechanisms and inflammatory cell activity in the clearance rate of rabbit vitreous blood clots were investigated using a previously described model. Increased fibrinolysis, induced by intravitreal injection of homologous plasmin or heterologous plasminogen activator, was associated with an increased clearance rate of vitreous blood clots as assessed by direct in vivo observation and by SDS-PAGE electrophoresis of vitreous whole blood clots. The induction of uveitis by non-fibrinolytic agents in eyes with vitreous clots was also associated with an increased clearance rate, but significantly less so than after fibrinolytic stimulation. Eyes treated with plasmin or plasminogen activator showed a marked increase in fibrin degradation products (FDP), predominantly FDP-D or D dimer, compared to eyes treated with non-fibrinolytic uveitic agents or to untreated eyes. It is suggested that the clearance rate of vitreous blood elots is primarily dependent on fibrinolytic activity in the vitreous, but that inflammatory cell activity is essential for the final removal of lysed blood clot debris, and that both mechanisms probably act synergistically during vitreous clot resolution.