Plasminogen activation at low temperatures in plasma samples containing therapeutic concentrations of tissue-type plasminogen activator or other thrombolytic agents

It is known that in vitro plasminogen activation in blood samples taken during thrombolytic therapy with tissue-type plasminogen activator (t-PA) may lead to artefactually low fibrinogen and α2-antiplasmin values. To mimic this phenomenon, pooled normal plasma was supplemented with 2.5 μg/ml t-PA and incubated at various temperature. The rates of fibrinogen degradation and α2-antiplasmin consumption were most pronounced at 37° C, were less pronounced at 25° C, but surprisingly, did not further decrease at 10° C, 0° C or -8° C. In contrast, when plasma was supplemented with 160 IU/ml urokinase or 30 IU/ml streptokinase, the rates of fibrinogen degradation and α2-antiplasmin consumption gradually decreased with incubation temperature and were negligible at 10° C and lower temperatures. The rate of plasminogen activation also decreased gradually with temperature in mixtures of purified fibrinogen, plasminogen, α2-antiplasmin and t-PA. These results imply that, in a plasma milieu, additional factors with a stimulatory activity are involved in t-PA-induced plasminogen activation at around 0° C. The abnormally high reaction rate at low temperatures explains in vitro plasminogen activation observed during the processing of t-PA-containing blood samples. In contrast to the activation of plasminogen by t-PA, the slow inhibition of t-PA (2.5 μ/ml) by proteinase inhibitors in plasma could be minimized to a negligible level by keeping the plasma samples at 0° C. This makes it possible to reliably monitor t-PA activity during thrombolytic therapy. Chemicals/CAS: plasminogen activator, 9039-53-6; streptokinase, 9002-01-1; tissue plasminogen activator, 105913-11-9; Chromogenic Compounds; Plasminogen, 9001-91-6; Streptokinase, EC 3.4.-; Tissue Plasminogen Activator, EC 3.4.21.68; Urinary Plasminogen Activator, EC 3.4.21.73