[Tissue plasminogen activator (t-PA) in myocardial infarction. Biological aspects].

A group of 37 patients with myocardial infarction less than 6 hours old was given 5,000 IU of heparin and 0.75 mg/kg of tissue plasminogen activator (rt-PA) (Group A, N = 18) or placebo (Group B, N = 19) intravenously over 90 minutes in a double blind study. Blood sampling was performed before, during and after treatment. The plasma rt-PA concentrations (micrograms/ml) of Group A were as follows: (Table: see text) The concentrations of plasminogen and antiplasmin have decreased significantly as did the fibrinogen level: a concentration of 1 g/l was observed in 7 cases during rt-PA therapy, lasting for 4 to 8 hours after the end of the infusion of rt-PA in 3 cases. The increase of FDP during rt-PA (m = 551 and 222 micrograms/ml at the 60th and 90th minutes) was relatively moderate considering the average level of defibrination (61%). No significant biological changes were observed in Group B. These results support those of our in vitro trials: at comparable thrombolytic activities, the reduction of plasma fibrinogen is less with rt-PA than with streptokinase (SK) or urokinase (UK). However, at concentrations 1 microgram/ml, rt-PA causes almost complete defibrination.