Department of Psychology, University of New Mexico, Albuquerque, 87111, USA.
Biol Rev Camb Philos Soc. 2012 Nov;87(4):856-73. doi: 10.1111/j.1469-185X.2012.00226.x. Epub 2012 May 8.
Throughout the second and third trimesters, the human placenta (and the placenta in other anthropoid primates) produces substantial quantities of corticotropin-releasing hormone (placental CRH), most of which is secreted into the maternal bloodstream. During pregnancy, CRH concentrations rise over 1000-fold. The advantages that led selection to favour placental CRH production and secretion are not yet fully understood. Placental CRH stimulates the production of maternal adrenocorticotropin hormone (ACTH) and cortisol, leading to substantial increases in maternal serum cortisol levels during the third trimester. These effects are puzzling in light of widespread theory that cortisol has harmful effects on the fetus. The maternal hypothalamic-pituitary-adrenal (HPA) axis becomes less sensitive to cortisol during pregnancy, purportedly to protect the fetus from cortisol exposure. Researchers, then, have often looked for beneficial effects of placental CRH that involve receptors outside the HPA system, such as the uterine myometrium (e.g. the placental clock hypothesis). An alternative view is proposed here: the beneficial effect of placental CRH to the fetus lies in the fact that it does stimulate the production of cortisol, which, in turn, leads to greater concentrations of glucose in the maternal bloodstream available for fetal consumption. In this view, maternal HPA insensitivity to placental CRH likely reflects counter-adaptation, as the optimal rate of cortisol production for the fetus exceeds that for the mother. Evidence pertaining to this proposal is reviewed.
在第二和第三个三个月期间，人类胎盘（和其他灵长类动物的胎盘）会产生大量的促肾上腺皮质激素释放激素（胎盘 CRH），其中大部分分泌到母体血液中。在怀孕期间，CRH 浓度增加了 1000 多倍。导致选择有利于胎盘 CRH 产生和分泌的优势还不完全清楚。胎盘 CRH 刺激母体内肾上腺皮质激素释放激素（ACTH）和皮质醇的产生，导致母体血清皮质醇水平在第三个三个月期间大幅增加。这些影响令人费解，因为广泛的理论认为皮质醇对胎儿有有害影响。在怀孕期间，母体下丘脑-垂体-肾上腺（HPA）轴对皮质醇的敏感性降低，据称是为了保护胎儿免受皮质醇暴露。因此，研究人员经常寻找涉及 HPA 系统以外的受体的胎盘 CRH 的有益作用，例如子宫平滑肌（例如胎盘时钟假说）。这里提出了另一种观点：胎盘 CRH 对胎儿的有益作用在于它确实会刺激皮质醇的产生，而皮质醇反过来又会导致母体血液中葡萄糖浓度增加，以供胎儿消耗。在这种观点中，母体 HPA 对胎盘 CRH 的不敏感可能反映了反适应，因为胎儿的皮质醇产生最佳率超过了母亲的皮质醇产生最佳率。审查了与该提议相关的证据。
