Oviductal plasminogen activator inhibitor-1 (PAI-1): mRNA, protein, and hormonal regulation during the estrous cycle and early pregnancy in the pig.

Recent identification of plasminogen activator inhibitor-1 (PAI-1) in the pig oviduct has prompted an evaluation of its mRNA, protein synthesis, and hormonal regulation during the estrous cycle and early pregnancy, defined as time prior to and after maternal recognition of pregnancy. To examine PAI-1 protein synthesis, oviductal tissue was collected from European Large White and Chinese Meishan gilts on days 0, 2, and 5 of early pregnancy, divided into three functional segments, and cultured. Culture media was collected and de novo synthesized PAI-1 analyzed by 2D-SDS-PAGE, fluorography, and densitometry. To determine hormonal regulation of PAI-1 synthesis and secretion, four groups of ovariectomized (OVX) cross-bred gilts were each treated with one of four steroid regimens (corn oil, estrogen, progesterone, or estrogen + progesterone) and tissue collected for RNA or cultured. Steady-state mRNA levels of PAI-1 were evaluated throughout the estrous cycle in cross-bred gilts. To compare steady-state PAI-1 mRNA levels between cyclic and pregnant cross-bred gilts, tissue was collected on days 0, 2, and 12. Quantitative analysis of steady-state levels of PAI-1 mRNA were analyzed by dot-blot hybridization and densitometry. A greater (P < 0.01) synthesis and secretion of PAI-1 protein was found in the isthmus portion of the oviduct relative to either the ampulla or infundibulum regardless of day of pregnancy or breed. No difference could be detected for PAI-1 protein between breeds. The Large White had a greater (P < 0.05) secretion of PAI-1 on day 2 of early pregnancy relative to other days examined. Whole oviductal tissue from cross-bred gilts was found to have a significantly greater amount of PAI-1 mRNA on days 1 and 2 compared to other days examined, while the isthmus had significantly greater levels of mRNA on days 2 and 12. A significant effect of day and segment was detected for levels of PAI-1 mRNA from cyclic and early pregnant cross-bred gilts. PAI-1 mRNA was found to be significantly greater in the isthmus than other segments, regardless of day of the estrous cycle or pregnancy. An interaction was detected for estrogen and progesterone on PAI-1 mRNA (P < 0.05) and protein (P = 0.09). Estrogen was found to inhibit PAI-1 protein synthesis and also inhibited progesterone-mediated stimulation of PAI-1 mRNA. Our results demonstrate expression of PAI-1 mRNA and protein are highest on day 2 of early pregnancy, which is consistent with its proposed function of protecting the oocyte/embryo from enzymatic degradation and/or extracellular matrix remodeling of both oviduct and early cleavage-stage embryo.