Changes in plasma levels of tissue plasminogen activator and its inhibitor in aged myocardial infarction patients.

Plasma levels of tissue plasminogen activator (tPA) antigen, tPA activity and plasminogen activator inhibitor (PAI) activity were determined in 40 cases of acute myocardial infarction (AMI) at the onset and 2-4 weeks after the onset of the disease. 24 healthy subjects served as controls. At the onset of AMI, mean plasma level of tPA antigen was significantly higher than that of control subjects (13.5 +/- 4.8 ng/ml vs 6.4 +/- 2.0 ng/ml), with the highest elevation in the group greater than 65 years of age. Mean plasma level of tPA activity was significantly lower than in the controls (1.1 +/- 0.4 IU/ml vs 1.6 +/- 0.4 IU/ml), especially in patients over 65 years of age. Mean plasma level of PAI activity was significantly higher than in the controls (17.5 +/- 12.0 AU/ml vs 9.0 +/- 4.6 AU/ml), especially in patients over 65 years of age. At 2-4 weeks, mean plasma levels of tPA and PAI activities of AMI patients had dropped to 1.5 +/- 0.6 IU/ml and 9.5 +/- 8.9 AU/ml, respectively, not significantly different from controls. The tPA antigen had come down to 11.0 +/- 5.4 ng/ml, but still higher than in the controls. The possible mechanism of these phenomena was discussed.