de Ruijter-Villani M, van Tol H T A, Stout T A E
Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112, 3584 CM Utrecht, The Netherlands.
Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 104, 3584 CM Utrecht, The Netherlands.
Reprod Fertil Dev. 2015 Jun;27(5):834-45. doi: 10.1071/RD13381.
Endometrial oxytocin receptors (OXTR) and prostaglandin-endoperoxide synthase 2 (PTGS2) are central components of the luteolytic pathway in cyclic mares, and their suppression is thought to be critical to luteal maintenance during early pregnancy. We examined the effect of pregnancy on endometrial expression of potential regulators of prostaglandin (PG) F2α secretion in mares. Expression of the nuclear progesterone receptor and oestrogen receptor ERα was high during oestrus, and depressed when progesterone was elevated; the opposite applied to the membrane progesterone receptor. PTGS2 was upregulated on Day 14 of dioestrus, but not pregnancy. Although OXTR mRNA expression was not elevated on Day 14 of dioestrus, protein abundance was; this increase in OXTR protein was absent on Day 14 of pregnancy. Intriguingly, gene and protein expression for PTGS2 and OXTR increased markedly between Days 14 and 21 of pregnancy suggesting that, although initial avoidance of luteolysis during pregnancy involves their suppression, this is a transient measure that delays rather than abolishes luteolytic pathway generation. The only oxytocin-PGF2α feedback loop component downregulated on both Days 14 and 21 of pregnancy was the PGF2α receptor we propose that downregulation of the PGF2α receptor uncouples the oxytocin-PGF2α feedback loop, thereby preventing generation of the large PGF2α pulses required for luteolysis.
子宫内膜催产素受体（OXTR）和前列腺素内过氧化物合酶2（PTGS2）是周期性母马黄体溶解途径的核心组成部分，它们的抑制被认为对妊娠早期黄体的维持至关重要。我们研究了妊娠对母马子宫内膜中前列腺素（PG）F2α分泌潜在调节因子表达的影响。核孕酮受体和雌激素受体ERα的表达在发情期较高，而在孕酮升高时降低；膜孕酮受体则相反。PTGS2在发情后期第14天上调，但在妊娠时未上调。尽管在发情后期第14天OXTR mRNA表达未升高，但其蛋白丰度升高；而在妊娠第14天，OXTR蛋白没有这种增加。有趣的是，PTGS2和OXTR的基因和蛋白表达在妊娠第14天至21天之间显著增加，这表明，尽管妊娠期间最初避免黄体溶解涉及对它们的抑制，但这是一种暂时的措施，只是延迟而不是消除黄体溶解途径的产生。在妊娠第14天和21天均下调的唯一催产素-PGF2α反馈环成分是PGF2α受体。我们提出，PGF2α受体的下调使催产素-PGF2α反馈环解偶联，从而阻止了黄体溶解所需的大的PGF2α脉冲的产生。
