Tissue plasminogen activator activity in human aqueous humor.
OBJECTIVE
To determine the levels of free plasminogen activator activity in human aqueous humor and to identify the type of activity (i.e., tissue-type t-PA or urokinase-type u-PA) that is responsible.


METHODS
Aqueous humor was obtained by a simplified pipette paracentesis before cataract surgery in 31 subjects, ages 57 to 93 years. Levels of plasminogen activator activity were determined using a modified 17-hour specific amidolytic assay. The type of plasminogen activator was investigated in selected samples based on its dependence on soluble fibrin, inhibition by amiloride, and specific antibody blocking. Activity-antigen ratios were compared in seven samples.


RESULTS
Plasminogen activator (PA) activity was present in all samples tested. PA activity ranged widely between 0.54 and 26.7 mIU/ml, with a mean value of 10.8 +/- 8.1 mIU/ml. Soluble fibrin, a known stimulator of tissue-type plasminogen activator (t-PA), was required in the assay system. Its absence decreased the measured activity by more than 90%. Amiloride, a known inhibitor of urokinase-type PA, had little or no effect in selected samples tested. The activity was blocked by anti-human t-PA antibodies but not by antibodies against human u-PA, further defining the type of PA responsible for the detected activity. t-PA antigen levels showed less variation among individuals than did activity levels. Antigen-activity ratios ranged between 89 and 552.


CONCLUSIONS
Plasminogen activator activity is present in the human aqueous humor in measurable quantities. The type of PA activity present is almost exclusively t-PA. t-PA activity varies more widely than antigen, as is the case in plasma.
Smalley
D M
DM
Department of Pathology, University of Connecticut Health Center, Farmington.
Fitzgerald
J E
JE
Taylor
D M
DM
Cone
R E
RE
O'Rourke
J
J
D000368:Aged; D000369:Aged, 80 and over; D000584:Amiloride; D001082:Aqueous Humor / Q000737:chemistry*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005337:Fibrin; D006801:Humans; D008297:Male; D008875:Middle Aged; D010958:Plasminogen; D010959:Tissue Plasminogen Activator / Q000032:analysis*; D014568:Urokinase-Type Plasminogen Activator / Q000032:analysis
D000584:Amiloride; D005337:Fibrin; D010958:Plasminogen; D010959:Tissue Plasminogen Activator; D014568:Urokinase-Type Plasminogen Activator