Clinic for Obstetrics, Gynaecology and Andrology of Large and Small Animals, Justus-Liebig-University Giessen, Frankfurter Strasse 106, D-35392 Giessen, Germany.
Reproduction. 2012 Aug;144(2):279-92. doi: 10.1530/REP-11-0471. Epub 2012 Jun 8.
A pronounced increase in fetal cortisol concentrations stimulating an increase in estrogen production at the expense of progesterone precursors in the placenta, luteolysis, and progesterone withdrawal is considered as a key event during the complex signal cascade leading to the initiation of parturition in cattle. However, there are many questions concerning the exact functional and/or temporal relationships between these individual processes which finally result in the expulsion of the calf and the timely release of the placenta. Thus, parturition was induced in 270-day pregnant cows using the progesterone receptor blocker aglepristone (group AG, n=3), the prostaglandin F(2α) analog cloprostenol (group PG, n=4), and the glucocorticoid dexamethasone (group GC, n=4) to characterize the effect on maternal steroid and prostaglandin levels and to identify immediate subsequent changes in placental morphology and gene expression as compared with untreated controls sampled on day 272 (group D272, n=3) and cows during normal parturition (group NT, n=4). All calves of the treatment groups were born on days 271-272, whereas gestational length in NT cows was 280.5±1.3 days. However, none of the treatments significantly induced the prepartal remodeling of placentomes characterized by a decline in trophoblast giant cells and reduction of the caruncular epithelium. Data on placental CYP17 and COX2 expression confirm that these key enzymes are upregulated by GC, whereas placental aromatase expression was not affected by any treatment. Maternal progesterone and prostaglandin profiles suggest differential effects of the treatments on luteal function and placental or uterine prostaglandin production. The results provide new information on the initiation of parturition in cattle but raise many new questions.
胎儿皮质醇浓度的显著增加刺激雌激素的产生，而这是以胎盘、黄体溶解和孕酮撤退为代价的孕酮前体增加，被认为是导致牛分娩开始的复杂信号级联中的一个关键事件。然而，关于这些单个过程之间的确切功能和/或时间关系仍有许多问题，这些过程最终导致小牛的排出和胎盘的及时释放。因此，使用孕酮受体阻滞剂 aglepristone（AG 组，n=3）、前列腺素 F(2α)类似物 cloprostenol（PG 组，n=4）和糖皮质激素地塞米松（GC 组，n=4）在 270 天妊娠的奶牛中诱导分娩，以研究其对母体类固醇和前列腺素水平的影响，并确定与未经处理的对照组（第 272 天采样，D272 组，n=3）和正常分娩的奶牛（NT 组，n=4）相比，胎盘形态和基因表达的即时后续变化。所有治疗组的小牛都在第 271-272 天出生，而 NT 组奶牛的妊娠期为 280.5±1.3 天。然而，没有一种治疗方法能显著诱导胎盘盘状结构的产前重塑，其特征是滋养层巨细胞减少和肉阜上皮减少。关于胎盘 CYP17 和 COX2 表达的数据证实，这些关键酶被 GC 上调，而任何治疗都不会影响胎盘芳香化酶的表达。母体孕酮和前列腺素谱表明，这些处理对黄体功能和胎盘或子宫前列腺素产生有不同的影响。这些结果提供了关于牛分娩开始的新信息，但也提出了许多新的问题。
