Occurrence of both urokinase and tissue plasminogen activator in the human endometrium.

The presence of two different plasminogen activators, urokinase and tissue activator, in the endometrium was demonstrated immunologically. Tissue activator was prevalent and urokinase was present in only minor amounts in endometrial tissue extractions. In tissue culture, on the contrary, endometrial explants released more urokinase than tissue activator into the medium and the fibrinolytic activity of the medium was mainly due to urokinase. This may reflect different modes of intracellular storage of the two activators, or the presence of a pre-urokinase which is immunologically different from urokinase and which is activated upon release. The amount of urokinase and fibrinolytic activity released into the culture medium was higher when endometrium samples had been obtained in the midcycle phase than in the proliferative and luteal phases. This pattern mimics the in vivo release of plasminogen activator from the endometrium into the uterine fluid. Endometrium obtained from IUD-users had a higher content of urokinase than that obtained from non-users.