Summary
The influence of the inhibitors of plasminogen activation by streptokinase, urokinase
and tissue activator and of the two antiplasmins i.e. α1 antitrypsin and α2-macroglobulin, upon the formation and clearance of streptokinase-activator in vivo
was investigated in 22 subjects. No influence of the above mentioned inhibitors on
the formation of the streptokinase-activator could be found, whereas the clearance
of the activator seems to be a function of the α2-macroglobulin level before streptokinase administration. The clearance rate of the
streptokinase-activator differed significantly from the clearance rate of 131I labelled streptokinase caused by antigen-antibody complex formation [Fletcher et
al. (10)], and was similar to the clearance rate of the histamine or nicotinic acid
induced plasminogen activator. The possibility of a common clearing mechanism of fibrinolytic
activators is discussed.
The existence of 3 different inhibitors activities on plasminogen activation as tested
in vitro i. e. inhibitor of streptokinase, urokinase and tissue activator, was demonstrated.
These inhibitory activities are probably not the properties of 3 different serum proteins
but rather the result of the action of α1antitrypsin and α2-macroglobulin. The degree of inhibition, however, of each of the 2 proteins on each
of the 3 plasminogen activators (streptokinase, urokinase and tissue activator) seems
to be different. This difference may be caused by a different inhibitory effect of
α1 antitrypsin or α2-macroglobulin on each of the plasminogen activators.
The plasmin formed after the streptokinase infusion is rapidly bound by the α2macroglobulin and this plasmin-antiplasmin complex is immediately removed from the
blood, causing a decrease of the α2-macroglobulin level. This decrease of α2-macroglobulin is correlated with the initial level of α2-macroglobulin. This finding demonstrates the concentration depending formation of
the plasmin-antiplasmin complex also in vivo.
