Gene expression of estrogen and oxytocin receptors in the uterus of pregnant and parturient bitches

In the canine species, the precise mechanisms of pregnancy maintenance and the initiation of parturition are not completely understood. The expression of genes encoding the receptors for estrogen (ERα mRNA) and oxytocin (OTR mRNA) was studied in the endometrium and myometrium during pregnancy and parturition in dogs. Real-time PCR was performed to quantify the levels of ERα mRNA and OTR mRNA in the uterus of bitches during early (up to 20 days of gestation), mid (20 to 40 days) and late pregnancy (41 to 60 days), and parturition (first stage of labor). All tissues expressed ERα and OTR mRNA, and are thus possibly able to respond to eventual estrogen and oxytocin hormonal stimuli. No statistically significant differences in the expression of ERα mRNA were verified in the endometrium and myometrium throughout pregnancy and parturition, but expression of OTR mRNA increased at both parturition and late pregnancy. We concluded that the increase of endometrial and myometrial OTR mRNA expression in dogs is not an event dependent on estrogenic stimulation. Moreover, the contractility response of the canine uterus to oxytocin begins during pregnancy and maintains myometrial activity. The expression of OTR mRNA in canine uterine tissues varied over time, which supports an interpretation that the sensitivity and response to hormone therapy varies during the course of pregnancy and labor. Further studies are needed to elucidate the factors underlying the synthesis of uterine oxytocin receptors and the possible role of ERβ rather than ERα in the uterine tissues during pregnancy and parturition in dogs.

犬类妊娠维持与分娩启动的确切机制目前尚未完全阐明。本研究针对犬妊娠及分娩阶段的子宫内膜（endometrium）与子宫肌层（myometrium）内，编码雌激素受体α mRNA（ERα mRNA）与催产素受体mRNA（OTR mRNA）的基因表达情况展开了探究。采用实时荧光定量PCR（real-time PCR）技术，对妊娠早期（妊娠天数≤20天）、中期（20~40天）、晚期（41~60天）以及分娩期（产程第一阶段）的母犬子宫组织中ERα mRNA与OTR mRNA的表达水平进行了定量检测。所有受试组织均表达ERα与OTR mRNA，因此理论上可对雌激素及催产素的激素刺激产生响应。在整个妊娠及分娩阶段，子宫内膜与子宫肌层内ERα mRNA的表达水平均未出现具有统计学意义的显著差异，但OTR mRNA的表达水平在分娩期与妊娠晚期均有所升高。本研究得出结论：犬子宫内膜与子宫肌层内OTR mRNA表达水平的升高，并非依赖于雌激素刺激。此外，犬子宫对催产素的收缩响应始于妊娠阶段，并可维持子宫肌层的收缩活性。犬子宫组织中OTR mRNA的表达水平随时间动态变化，这一结果支持"妊娠及产程中，子宫对激素治疗的敏感性与响应能力存在差异"这一推论。未来仍需开展进一步研究，以阐明犬子宫催产素受体合成的潜在调控因子，以及妊娠与分娩阶段子宫组织中雌激素受体β（ERβ）而非ERα可能发挥的作用。