Cyclic variation of plasminogen activation in human uterine fluid and the influence of an intrauterine device.

Activation of plasminogen to plasmin in uterine fluid results in the formation of plasmin-alpha 2-antiplasmin complexes. The degree of plasminogen activation was studied during the menstrual cycle in IUD-users and nonusers. The absence of free plasminogen in the presence of plasmin complexes indicated complete activation of the zymogen. The simultaneous occurrence of free plasminogen and plasmin complexes were interpreted to represent incomplete activation. Results were correlated with the concentration of alpha 2-antiplasmin, a major inhibitor of urokinase and plasmin. In the midcycle phase of IUD-non-users, plasminogen activation was complete and the concentration of alpha 2-antiplasmin was low. In the luteal phase of the same population the concentration of alpha 2-antiplasmin was high and there was no plasminogen activation. In contrast, IUD-users generally had an incomplete activation of plasminogen throughout the menstrual cycle. Also, their concentrations of alpha 2-antiplasmin were increased in the proliferative and midcycle phases.