Ovarian steroids, oxytocin, and tumor necrosis factor modulate equine oviduct function

The oviduct plays important roles in the early reproductive process. The aim of this study was to evaluate gene transcription and protein expression of progesterone receptor (PGR), estrogen receptors 1 (ESR1) and 2 (ESR2); oxytocin receptor (OXTR); prostaglandin F2α synthase (AKR1C3), and prostaglandin E2 synthase (Ptges) in mare oviduct in different estrous cycle stages. Estradiol (E₂), progesterone (P₄), oxytocin (OXT), and tumor necrosis factor α (TNF) effect on in vitro PGE₂ and prostaglandin F2α (PGF_2α) secretion by equine oviduct explants or by oviductal epithelial cells (OECs) were also assessed. During the breeding season, oviduct tissue was obtained post mortem from cyclic mares. Protein of ESR1, ESR2, PGR, AKR1C3, and Ptges was present in OECs, whereas OXTR was shown in oviduct stroma. In follicular phase, protein expression of ESR1, ESR2, PGR, and OXTR increased in oviduct explants (P < 0.05), whereas no estrous cycle effect was noted for AKR1C3 or Ptges. In follicular phase, mRNA transcription was upregulated for Pgr but downregulated for Oxtr, Ptges, and Akr1c3 (P < 0.05). Nevertheless, Esr1 and Esr2 mRNA levels did not change with the estrous cycle. In the ampulla, Esr1, Esr2, and Oxtr mRNA transcription increased, but not for Pgr or Ptges. In contrast, Akr1c3 mRNA level was upregulated in the infundibulum (P < 0.05). In follicular phase, E₂, P₄, and OXT downregulated PGE₂ production by OEC (P < 0.05), but no difference was observed in mid-luteal phase. Explants production of PGE₂ rose when treated with OXT in follicular phase; with TNF or OXT in early luteal phase; or with TNF, OXT, or P₄ in mid-luteal phase. PGF_2α production by OEC was downregulated by all treatments in follicular phase but upregulated in mid-luteal phase (P < 0.05). Oviduct explants PGF_2α production was stimulated by TNF or OXT in all estrous cycle phases. In conclusion, this work has shown that ESR1, ESR2, OXTR, Ptges, and AKRLC3 gene transcription and/or translation is estrous cycle dependent and varies with oviduct portion (infundibulum vs ampulla) and cell type. Ovarian steroid hormones, OXT and TNF stimulation of PGF_2α and/or PGE₂ production is also estrous cycle dependent and varies in the different portions of mare oviduct. Differential transcription level and protein localization in various portions of the oviduct throughout the estrous cycle, as well as PG production, suggest coordinated physiologic actions and mechanisms of steroid hormones, OXT, and TNF in the equine oviduct.