| Abstract: | Two types of plasminogen activator (PA), t-PA (tissue type) and u-PA (urokinase type), are released from endometrial tissue in organ culture, as judged by immunological identification and molecular weight. Addition of estradiol to the medium greatly enhanced the release of u-PA, whereas that of t-PA was not low. Addition of progesterone, on the other hand, after priming of the endometrial tissue with estradiol, resulted in a much lower release of both types of PA. This pattern of PA release in response to hormonal stimulation in vitro agrees with previous observations of the PA activity of endometrial secretion in vivo. Endometrial tissue also released a PA inhibitor with molecular weight of approximately 50,000, which complexed both t-PA and u-PA. In cultures stimulated with estradiol the amount of free u-PA increased gradually during incubation and minor amounts of free t-PA appeared after 4-6 days culture. The amount of complexes, and thus the amount of PA inhibitor also increased under influence of estradiol. In cultures stimulated with progesterone, on the other hand, only minor amounts of free u-PA and no free t-PA was detected. The inhibitor might be of either the endothelial or the placental type, or both. |
