The serpin ␣ 2 -antiplasmin ( ␣ 2 -AP) is the major circulating inhibitor of plasmin; it plays a determining role in the regulation of intravascular fibrinolysis. In addition to blood plasma, plasmin formation occurs in various organs where it is thought to fulfill a spectrum of functions not restricted to clot lysis. ␣ 2 -AP is synthesized by hepatocytes, but other possible sites of production have not been investigated. To explore the potential extravascular contribution of ␣ 2 -AP in the regulation of proteolysis, we have isolated the murine ␣ 2 -AP cDNA and determined its mRNA distribution in adult tissues.In

A search for inhibitors of urokinase-type plasminogen activator (uPA) in the male and female murine genital tracts revealed high levels of a uPA ligand in the seminal vesicle. This ligand is functionally, biochemically and immunologically indistinguishable from protease-nexin I (PN-I), a serpin ligand of thrombin and uPA previously detected only in mesenchymal cells and astrocytes. A survey of murine tissues indicates that PN-I mRNA is most abundant in seminal vesicles, where it represents 0.2-0.4% of the mRNAs. PN-I is synthesized in the epithelium of the seminal vesicle, as determined by in situ hybridization, and is secreted in the lumen of the gland. PN-I levels are much lower in immature animals, and strongly decreased upon castration. Testosterone treatment of castrated males rapidly restores PN-I mRNA levels, indicating that PN-I gene expression is under androgen control.

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