Ultrasound affects distribution of plasminogen and tissue-type plasminogen activator in whole blood clots in vitro

Ultrasound of 2 MHz frequency and 1.2 W/cm(2) acoustic intensity was applied to examine the effect of sonication on recombinant tissue-type plasminogen activator (rt-PA)-induced thrombolysis as well as on the distribution of plasminogen and t-PA within whole blood clots in vitro. Thrombolysis was evaluated quantitatively by measuring clot weight reduction and the level of fibrin degradation product D-dimer (FDP-DD) in the supernatant. Weight reduction in the group of clots treated both with ultrasound and rt-PA was 35.2% +/- 6.9% which is significantly higher (p < 0.0001) than in the group of clots treated with rt-PA only (19.9% +/- 4.3%). FDP-DD level in the supernatants of the group treated with ultrasound and rt-PA increased sevenfold compared to the group treated with rt-PA alone, (14895 +/- 2513 ng/ml vs. 2364 +/- 725 ng/ml). Localization of fibrinolytic components within the clots was, accomplished by using gel-entrapping technique and immunohistochemistry. Spatial distributions of t-PA and plasminogen showed clearly that ultrasound promoted the penetration of rt-PA into thrombi significantly (p < 0.0001), and broadened the zone of lysis from 8.9 +/- 2.6 mum to 21.2 +/- 7.2 mum. We speculate that ultrasound enhances thrombolysis by affecting the distribution of rt-PA within the clot.