Protease‐nexin I as an androgen‐dependent secretory product of the murine seminal vesicle

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.