Molecular and functional properties of fetal plasminogen and its possible influence on clot lysis in the neonatal period.

The blood fibrinolytic system essentially consists of proteolytic enzyme activation processes leading to the formation of the fibrin-degrading enzyme plasmin. It is thus the counterpart of the blood coagulation system. It differs physiologically in newborns compared with adults. In newborns, the plasma levels of plasminogen, the inactive plasmin precursor, are relatively low, and a correlation between maturity and plasminogen levels is observed. Newborn plasminogen has been purified, characterized, and compared with adult plasminogen and does exist in a fetal form with an increased concentration of sialic acid, similar to fetal fibrinogen. We review the molecular and functional properties of fetal plasminogen and its possible influence on clot lysis and thrombolytic therapy in the neonatal period.