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Establishment of pregnancy in pigs requires continuous function of corpora lutea and endometrial preparation for embryo implantation. Progesterone regulates expression of many proteins necessary for endometrial remodelling and embryo-maternal communications. Attaining the uterine receptivity involves progesterone priming and loss of progesterone receptors in the uterine epithelium before days 10-12 after oestrus. Spermatozoa and oocytes in oviduct alter secretion of specific proteins that exert beneficial effect on gametes and embryos. Moreover, an appropriate leucocyte activation and maintenance of delicate cytokine balance within the oviduct and uterus are important for early pregnancy. This early local immune response is rather mediated by seminal plasma components. These components also influence prostaglandin (PG) synthesis in the oviduct that is important for gamete and embryo transport. Pregnancy establishment requires the biphasic pattern of oestrogen secretion by conceptuses on days 11-12 and 15-30. Conceptus affects lipid signalling system consisting of prostaglandins and lysophosphatic acid. PG synthesis is changed by conceptus signals in favour of luteoprotective PGE(2) . Additionally, existence of PGE(2) positive feedback loop in the endometrium contributes to increased PGE(2) /PGF(2α) ratio during the peri-implantation period. PGE(2) through endometrial PGE(2) receptor (PTGER2) elevates the expression of enzymes involved in PGE(2) synthesis. Higher PGE(2) secretion in uterine lumen coincides with the elevated expression of HOXA10 transcription factor critical for implantation. A stable adhesion between conceptus and endometrium requires reduction in mucin-1 on the apical surface of epithelium and integrin activation by extracellular matrix proteins. Furthermore, growth factors, cytokines and its receptors are involved in embryo-maternal interactions.

To cope with rising demands for increased blood supply during pregnancy, the vasculature of the uterus undergoes several adaptive changes, including increased permeability, angiogenesis and vasodilatation. Although it is clear that vascular endothelial growth factor (VEGF) plays a paramount role in achieving these adaptations, little is known about regulation of VEGF expression in endometrium during pregnancy. Thus, we have investigated whether luteinizing hormone (LH) and tumour necrosis factor-alpha (TNFalpha) may affect VEGF secretion by stromal cells during early pregnancy in pigs. Real-time reverse transcription/polymerase chain reaction (RT/PCR) of VEGF120 and VEGF164 gene expression revealed significantly higher levels of VEGF164 mRNA in cultured stromal cells (p < 0.0001). The LH-stimulated secretion of VEGF was detected after 24 and 48 h of treatment when doses 50 and 100 ng/ml were used (p < 0.05 and p < 0.01, respectively). The TNFalpha-induced secretion of VEGF by stromal cells was detected only after 24-h treatment with the highest dose used in the experiment (50 ng/ml; p < 0.05). Although the influence of LH on VEGF secretion was more visible compared with TNFalpha, both factors may be considered as potential modulators of adaptive changes in uterine vasculature occurring during pregnancy in the pig.

Contents Cyclooxygenase (COX) is the rate-limiting enzyme that catalyses the initial step in prostaglandins (PGs) production. In the present studies, endometrial COX-1 and COX-2 expression throughout the oestrous cycle and early pregnancy was analysed in pigs using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), Western blot and immunohistochemistry. There were no changes in messenger RNA (mRNA) and protein expression for COX-1 in cyclic pigs. In pregnant animals, mRNA levels of this enzyme increased on days 22–25 (p