Regulatory effect of contraceptive steroids on the release of tissue-type plasminogen activator in vitro

The release of tissue-type plasminogen activator (t-PA) from incubated specimens of human veins was investigated by an immunoradiometric determination of the concentration of t-PA in the medium. The initial release of t-PA was strongly correlated to the weight of the incubated specimens. T-PA was not demonstrable after the third day of incubation. The addition of d-norgestrel (83.3 ng/ml) to the medium significantly stimulated the release of t-PA; whereas, ethinylestradiol (16.6 ng/ml) did not have an effect.