Among domestic animal species, the reproductive biology of the dog belongs to the most peculiar. This includes the conceptus-maternal communication and endocrine mechanisms involved in maintenance of pregnancy. Dogs fully depend on luteal progesterone (P4) throughout pregnancy, with similar steroid secretion patterns in pregnant and non-pregnant bitches until prepartum luteolysis. Thus, dogs lack the classical recognition of pregnancy. The luteal P4 is the most important hormone regulating the onset and maintenance of pregnancy in previously estrogenized bitches. Although the canine uterus is exposed to high P4 levels, decidualization is not spontaneous but induced by the presence of embryos. Following implantation, decidualization continues, associated with development of the invasive endotheliochorial placenta, leading to establishment of maternal decidual cells expressing the nuclear P4 receptor (PGR). Consequently, although not producing steroids, the canine placenta remains highly sensitive to circulating ovarian steroids. The placental conceptus-maternal communication is responsible for the maintenance of pregnancy, with functional withdrawal of PGR evoking a luteolytic cascade with prepartum PGF2α release. The fetal trophoblast is the major source of prepartum placental prostaglandins. This conceptus-maternal communication is unique to the dog and has clinical implications. Due to luteal steroids, there is no prepartum estradiol increase. Elevated cortisol levels are observed irregularly. This emphasizes the unique character of canine reproductive physiology and the challenges in transferring translational research to the dog. Further research is needed for better understanding of canine reproduction and improving clinical protocols, including the latest results obtained from applying modern laboratory technologies such as the transcriptomic approach.

中文翻译：

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维持和终止妊娠期间犬概念-母体的交流，包括物种特异性蜕膜化的作用。

家养动物物种中，狗的生殖生物学属于最奇特的。这包括维持妊娠所涉及的孕产妇沟通和内分泌机制。狗在整个怀孕期间完全依赖黄体孕酮 (P4)，怀孕和非怀孕母犬的类固醇分泌模式相似，直到产前黄体溶解。因此，狗缺乏对怀孕的经典识别。黄体 P4 是最重要的激素，可调节先前雌激素化的母犬的怀孕开始和维持。虽然犬子宫暴露于高 P4 水平，蜕膜不是自发的，而是由胚胎的存在诱导的。植入后，蜕膜继续，与侵入性内皮层胎盘的发展有关，导致建立表达核 P4 受体 (PGR) 的母体蜕膜细胞。因此，虽然不产生类固醇，但犬胎盘仍然对循环的卵巢类固醇高度敏感。胎盘概念-母体沟通负责维持妊娠，PGR 的功能性退出引起产前 PGF2α 释放的黄体溶解级联反应。胎儿滋养层是产前胎盘前列腺素的主要来源。这种概念-母体交流是狗独有的，具有临床意义。由于黄体类固醇，产前雌二醇不会增加。不规则地观察到升高的皮质醇水平。这强调了犬生殖生理学的独特特征以及将转化研究转移到犬身上的挑战。