Histochemical study of fibrinolytic activity in the rat uterus in normal and hormonally induced estrus

The fibrinolytic activity of the rat uterus was studied by a histochemical method enabling localization of the activity in the tissues. The activity was caused by a plasminogen activator present in the blood vessels of the uterus. While the fibrinolytic activity in the myometrial vessels changes little, the increase of vascularity at late estrus is accompanied with an increase in fibrinolytic activity of the vessels in the endometrium. After ovariectomy, atrophy of uterus and decrease in endometrial vascularity was associated with loss of fibrinolytic activity. This was reversed by estrogen administration. Progestrone administration following estrogen withdrawal produced a secretory stage with no or only a trace of fibrinolytic activity in the endometrium.