Human ureter, a source of tissue plasminogen activator.

In organ cultures of human ureters, plasminogen activators were released into the medium. Unlike most tissue cultures that release mainly urokinase (UK), the activators released by ureter cultures were predominantly of the tissue-type (t-PA), as shown by radioimmunoassay. Using affinity chromatography it was possible to distinguish two activities. One minor fraction was quenched by antibodies against UK, but not by antibodies against t-PA. The other activity was quenched by antibodies against t-PA, but not by those against UK, and required the presence of fibrin to activate plasminogen. Because of the large amount of t-PA, cells derived from human ureter might well prove to be a useful source of t-PA.