Identification and localization of plasminogen activator inhibitor-1 within the porcine oviduct

The porcine oviduct synthesizes de novo and secretes a number of proteins i nto culture medium, many of which are unidentified. The objectives of the p resent study were to 1) semipurify and identify a M-r 45 000 secreted prote in of the oviduct, 2) examine its synthesis within the three functional seg ments (infundibulum, ampulla, and isthmus), and 3) evaluate its distributio n throughout the oviduct. Oviductal tissue was collected during early pregn ancy, divided into functional segments, and subsequently cultured. Medium w as collected, and the M-r 45 000 protein was concentrated by gel-filtration chromatography. The semipurified protein was transferred onto a polyvinyli dene fluoride membrane and subjected to N-terminal amino acid analysis. The 26-amino acid sequence was 96% identical to that of pig plasminogen activa tor inhibitor (PAI)-1. Analysis by 1-dimensional SDS-PAGE and fluorography of rabbit anti-human PAI-1-immunoprecipitated product confirmed PAI-1. Subs equent 2-dimensional SDS-PACE and fluorographic analyses of media revealed greater PAI-1 synthesis by the isthmus than by the ampulla or infundibulum. PAI-1 was immunolocalized throughout the oviduct and was heavily concentra ted in the apical region of epithelial cells. Immunogold electron microscop y localized PAI-1 within putative secretory granules in the epithelial apic al region and also associated with cilia in the isthmus. Isthmic PAI expres sion suggests a crucial role in protecting the preimplantation embryo from proteolytic degradation as well as in regulation of extracellular matrix tu rnover and remodeling.