Urokinase-type plasminogen activator in rabbit tears. Comparison with human tears

Plasminogen activator activity was determined in stimulated normal rabbit tears, and was identified as being due to urokinase using specific antibodies. The activator activity is about 100-fold higher in rabbit tears than in human tears. The molecular weight of the activator was determined by fibrin zymography to be 40-50 kDa. However, a multiband pattern of urokinase-type antigen ranging in molecular weight from 60-70 kDa to 200 kDa was detected by immunoblotting. The 60-70 kDa protein was resistant to reduction. The antigen concentration is more than 100-fold higher than the concentration expected from the activity measurement, indicating that most of the urokinase in rabbit tears is in inactive form, such as in inhibitor or receptor complexes.