Rat Testicular Peritubular Cells in Culture Secrete an Inhibitor of Plasminogen Activator Activity1

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Abstract
Rat testicular peritubular cells in culture secrete an inhibitor of plasminogen activator (PA) activity. Conditioned serum-free medium from secondary cultures of peritubular cells (PcMEM) was concentrated and then fractionated by gel exclusion chromatography. Under native or denaturing conditions, PA inhibitor (PA-I) activity appeared in fractions having a molecular weight of approximately 55,000. The PA-I inhibited the tissue-type plasminogen activator, and also that of the two-chain form of urokinase, but not the one-chain form. Addition of guanidine HCl (4 M) to PcMEM resulted in a large increase of inhibitory activity. The 55,000 molecular weight PA-I band in PcMEM reacted with antibodies against plasminogen activator inhibitors produced by bovine vascular endothelial cells, or by human fibrosarcoma cells, as detected by immunoadsorption experiments, by immunoblotting, and by reverse fibrin autography. We describe other characteristics of the protease inhibitor produced by testicular peritubular cells, and we discuss its possible functions in the control of PA activity in the seminiferous tubule at different stages of spermatogenesis.