Edwards Phoebe D, Boonstra Rudy
Centre for the Neurobiology of Stress, Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada.
Centre for the Neurobiology of Stress, Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada.
Gen Comp Endocrinol. 2018 Apr 1;259:122-130. doi: 10.1016/j.ygcen.2017.11.012. Epub 2017 Nov 17.
Pregnancy is one of the defining characteristics of placental mammals. Key in the growth and development of the fetus during pregnancy are the dynamics of glucocorticoids (GCs) and their binding protein,corticosteroid-binding globulin (CBG), which determines how much of the GCs are free and biologically active. Out of more than 5000 species of placental mammals in 19 different orders, our understanding of the dynamics of maternal GCs and CBG during pregnancy is largely limited to the detailed study of 3 groups - sheep, laboratory rodents, and humans. The assumption is often made that what we see in these few species applies to the rest. To examine this generality, we compared patterns of maternal GCs over pregnancy from all placental mammals where data is available: in the blood of 13 species from 5 different orders and in metabolites in excreta in an additional 20 species from 9 orders. We found that maternal free GCs increase by late pregnancy in most taxa. This increase is achieved by either an increase in total GC secretion or a decrease in CBG. A major exception is found in the even-toed ungulates (sheep, cows, etc.) where maternal GCs and CBG remain stable, but where the fetal adrenals mature in late pregnancy and produce the majority of their own GCs. We conclude that patterns of change in maternal GCs and CBG during pregnancy are species-specific but are alternative means to the same end: increased fetal exposure to GCs in late pregnancy, which is essential for development.
怀孕是胎盘哺乳动物的一个决定性特征。孕期胎儿生长发育的关键在于糖皮质激素（GCs）及其结合蛋白——皮质类固醇结合球蛋白（CBG）的动态变化，CBG决定了有多少GCs处于游离状态并具有生物活性。在19个不同目下的5000多种胎盘哺乳动物中，我们对孕期母体GCs和CBG动态变化的了解很大程度上仅限于对三组动物的详细研究——绵羊、实验啮齿动物和人类。人们常常假定我们在这少数物种中观察到的情况适用于其他物种。为了检验这种普遍性，我们比较了所有有数据可查的胎盘哺乳动物孕期母体GCs的模式：来自5个不同目的13个物种血液中的情况，以及另外来自9个目的20个物种排泄物中代谢物的情况。我们发现，在大多数分类群中，母体游离GCs在怀孕后期会增加。这种增加是通过GCs总分泌量的增加或CBG的减少来实现的。一个主要的例外是偶蹄目动物（绵羊、牛等），其母体GCs和CBG保持稳定，但胎儿肾上腺在怀孕后期成熟并产生大部分自身的GCs。我们得出结论，孕期母体GCs和CBG的变化模式具有物种特异性，但都是为了实现同一个目的的不同方式：在怀孕后期增加胎儿对GCs的暴露，这对发育至关重要。
