CHANGES IN t-PA ACTIVITY AND INHIBITION AS PART OF THE ACUTE PHASE REACTION IN ACUTE MYOCARDIAL INFARCTION

Acute myocardial infarction (AMI) is accompanied by sequential fluctuations in several plasma proteins indicative of an acute phase reaction. Global screening tests (ECLT and WBCLT) have revealed temporary depression of systemic fibrinolysis. However, such tests do not allow definite conclusions regarding the specific variables involved.

In a prospective study of 34 patients with AMI we determined selected variables involved in fibrinolysis, and in addition we investigated whether any fluctuation was related to the development of leg vein thrombosis (isotope-technique) or due to AMI. Blood samples were collected on days 1,2,4,6,8 after admission and eight weeks (recovery) after discharge. Euglobulin fibrinolytic activity was determined on fibrin plates. The measured activity was lower in the initial acute period (≤ 48 h after AMI) than in the recovery period (p<0.05). The intrinsic fibrinolytic proactivators (representing more than 95% of the total activator potential of plasma) did not change during the period of study. Levels in the euglobulins of C1-inactivator (the main inhibitor of the intrinsic system) were constant during the first 48 hours. This suggests that the observed reduction represents t-PA activity and this was verified by specific assay of t-PA. The t-PA inhibition capacity in plasma was elevated in the initial acute period compared to the recovery period (week 8; p<0.05). C-reactive protein and fibrinogen followed another pattern with the highest plasma level at day 4 and day 6, respectively. Plasma levels of C1-inactivator increased slowly with a peak at day 8. There was no difference of the determined variables between the DVT negative and positive group, suggesting that the observed changes were due to myocardial injury. Our findings show that components of the fibrinolytic system take part in the acute phase reaction following AMI, and that this involves a brief, initial period of reduced fibrinolytic potential (<48h). The initial, high levels of t-PA inhibition deserve consideration in regard to the institution of thrombolytic therapy with t-PA. (Undertaken within the frame of ECAT).