THE HISTOCHEMICAL PATTERN OF MECHANICALLY OR CHEMICALLY INJURED RABBIT CORNEA AFTER APROTININ TREATMENT - RELATIONSHIPS WITH THE PLASMIN CONCENTRATION OF THE TEAR FLUID

Plasmin, a serine protease, was recently found to be involved in corne al ulcerative processes in humans and rabbits. In our experiments, pla smin activity was found in the tear fluid after mechanical and chemica l damage of the rabbit cornea, such as de-epithelization and burning w ith alkali. The plasmin concentrations in the tear fluid were dependen t on the severity of injury. The highest plasmin activity (2.0-3.0 mug ml-1) occurred after severe alkali damage to large areas of the corne a, and the lowest activity (0.4-1.0 mug ml-1) after mechanical injury (de-epithelization). Plasmin concentrations up to 1.0 mug ml-1 were as sociated with increased activities of lysosomal hydrolases in epitheli al cells and keratocytes beneath the epithelium. Plasmin activities in creased as the inflammatory reaction developed. When plasmin activity in the tear fluid was higher than 1.0 mug ml-1, inflammatory cells wer e found in the corneal stroma. Levels of 1.5-2.0 mug ml-1 were connect ed with higher numbers of inflammatory cells (particularly polymorphon uclear leukocytes) with increased activities of lysosomal hydrolases. Very high plasmin activities (2.5-3.0 mug ml-1) accompanied corneal ul cerative processes. The local application of aprotinin (Trasylol, Baye r), an inhibitor of plasmin, and also of some other proteases, was fou nd to be necessary for the healing of severe corneal injuries in which highly elevated plasmin activity in the tear fluid and inflammatory c ellulization of the cornea occurred (severe damage). It was beneficial in cases in which medium plasmin activity occurred in the tear fluid and inflammatory changes in the cornea were not too extensive. If used very early after injury, aprotinin prevents the appearance of high pl asmin activity in the tear fluid, reduces the invasion of inflammatory cells into the corneal stroma, and accelerates the healing. Even the corneal transparency is restored in many cases.