Tissue plasminogen activator in the trabecular endothelium

By quantitative analysis of tissue plasminogen activator (TPA) in the trabecular endothelium, corneal endothelium, and iris in the eyes of monkeys and dogs, we found significant levels of TPA activity. In a [125I]fibrin-coated well assay, the levels for the dog and monkey were, respectively: trabecular endothelium, 0.2 and 0.5; corneal endothelium, 0.8 and 0.5 IU per mg protein. The iris tissue showed high TPA activity, but its protein content could not be measured with the techniques employed. Activity in the aqueous humor was not detectable. By the ELISA technique, the values (in ng TPA/mg tissue protein) for the dog and monkey were, respectively: trabecular endothelium, 0.16 and 0.44; corneal endothelium, 0.48 and 0.92. Again, iris tissue showed high TPA activity, whereas the aqueous humor showed low activity (0.86 ng/ml). The data obtained with the two methods showed a reasonable consistency, although a direct comparison was not possible because two separate standards were used. The presence of TPA in the trabecular endothelium, corneal endothelium, and iris may be important in modulating the resistance to aqueous outflow under normal conditions as well as those of hyphema.