The effects of plasma fibronectin on the fibrinolytic system were studied in vitro.
Fibronectin caused a time and concentration-dependent increase (up to 99% with 330
ug/ml) in the amidolytic activity of tissue plasminogen activator (TPA) but not of
urokinase. In the presence of fibronectin the Km of the amidolytic activity of TPA
decreased without a change in Vmax. It also caused a concentration-dependent increase
in lys-plas-minogen activation by TPA (up to 825% with 375 ug/ml) and by urokinase
(up to 400% with 250 ug/ml), as well as in the amidolytic activity of plasmin (up
to 55% with 300 ug/ml). Fibronectin did not enhance the activation of glu-plasminogen.
In the presence of fibronectin the Km of lys-plasminogen activation decreased without
a change in Vmax. In purified systems fibronectin significantly shortened the clot
lysis time (CLT) by up to 28% and 30% in TPA- and plasmin-activated lysis, respectively.
The presence of Ca2+ did not change fibronectin’s effect on CLT. Clots of non-fibronectin-depleted plasma
were lysed up to about twice as fast as the clots of fibronectin-depleted plasma.
In conclusion, physiologic concentrations of fibronectin enhanced the fibrinolytic
system in vitro. Further studies will be required to elucidate the mechanisms involved
and to document whether fibronectin has a similar effect in vivo.
Keywords
Fibronectin - Tissue plasminogen activator - Urokinase - Plasmin - Plasminogen - Fibrinolysis
