Fibrinolytic activity and localization of plasminogen activator in bovine vitreous body and aqueous humor

The types, activities and concentrations of plasminogen activator (PA) were examined in the bovine vitreous body and aqueous humor. Molecular weights of PA in the vitreous body and aqueous humor were approximately 66 and 110 kilodaltons (kDa), respectively, as determined by fibrinolysis enzymography. These PA activities were neutralized by anti-human tissue PA (t-PA) IgG but not by anti-human urokinase PA (u-PA) IgG. Both findings indicated that the main PA in the vitreous body and aqueous humor is t-PA. The existence of u-PA could not be confirmed in intraocular fluids. Fibrinolytic activities measured by amidolytic assay were 0.12 +/- 0.01 IU/ml in the vitreous body and 0.04 +/- 0.02 IU/ml in the aqueous humor. High concentrations but relatively low fibrinolytic activities suggested that PA and PA inhibitor coexisted in the intraocular fluids. Moreover, unbound PA inhibitor was not detected by reverse fibrinolysis enzymography. The present study suggests that most of the PA inhibitor combines with PA and forms a complex. PA predominates over PA inhibitor in the intraocular fluids, whereas PA inhibitor predominates in the plasma. The results by Todd's fibrinolysis autography and immunohistochemical staining showed that t-PA was present in the corneal endothelial cells, which are in direct contact with the aqueous humor. This suggests that not only the vascular system but the corneal endothelial cells as well might be a source of the PA of the aqueous humor and possibly of the vitreous body also.