Cortisol at MR Mediate Fetal Physiologic/Genomic Effects

描述(申请人提供)：这些研究的总体目标是验证这样一种假设，即在妊娠的大部分时间里，胎儿中游离皮质醇的浓度通过高亲和力(皮质类固醇I型)盐皮质激素受体(MR)而不是低亲和力但较高容量的糖皮质激素受体(GR)来发挥生理作用。众所周知，分娩时胎儿肾上腺产生的高水平皮质醇对正常器官成熟非常重要，这些影响是由GR介导的。MR在妊娠中期胎儿组织中的存在表明，即使在胎儿成熟之前，也可能存在通过MR的低浓度皮质醇的影响。我们将测试皮质醇在MR受体上的作用是否通过肺和/或肾脏中特定的MR靶基因来调节胎儿体积的影响，以及是否通过海马体中的MR靶基因来调节下丘脑-垂体-肾上腺功能。组织中皮质类固醇的相对活性将与血浆皮质类固醇水平、11β-羟基类固醇脱氢酶和还原酶活性(11betaHSD)、组织中MR和GR水平以及改变基因表达的反式激活有关。MR靶基因，包括早期反应基因SGK和K-RAS，以及较慢诱导的ENaC、Na/K ATPase和5HT1A、MR和GR基因将被测试。为了验证这一假说，我们设计了以下实验：1)在胎儿肾上腺成熟前后(120-140天)，对妊娠晚期胎儿肺、肾、心脏、海马体、脑干和垂体等组织中MR和GR的蛋白、mRNA和内源性类固醇的相对占有率以及11betaHSD的活性进行定量：2)检测阻断胎儿MR受体对成人已知的MR介导的生理行为、肾功能和ACTH分泌的影响，以及对胎儿可能的MR介导的功能、肺液重吸收的影响；3)测试MR占用与这些生理效应之间的关系，以及拟在海马体、肾脏和胎肺中进行MR作用的靶基因；4)比较MR和GR联合占用对这些基因和生理作用的影响。

DESCRIPTION (provided by applicant): The overall goal of these studies is to test the hypothesis that for most of gestation, the concentrations of free cortisol in the fetus exert physiologic actions via the high affinity (corticosteroid type I) mineralocorticoid receptors (MR) rather than the lower affinity, but higher capacity, glucocorticoid receptors (GR). It is well established that the high levels of cortisol produced by the fetal adrenal at the time of delivery are important for normal organ maturation, and that these effects are mediated by GR. The presence of MR in fetal tissues as early as mid-gestation suggests that there may be effects of low concentrations of cortisol via MR, even before the time of fetal maturation. We will test whether cortisol action at MR receptors mediates effects on fetal volume through specific MR-target genes in the lung and/or kidney, and on hypothalamo pituitary-adrenal function via MR-target genes in the hippocampus. The relative activity of corticosteroids in the tissues will be related to plasma levels of corticosteroids, activity of 11beta-hydroxysteroid dehydrogenase and reductase activities (11betaHSD), levels of MR and GR in the tissue, and transactivation to alter gene expression. MR target genes, including the early response genes, Sgk and K-Ras, and more slowly induced genes for ENaC, Na/K ATPase and 5HT1A, MR and GR will be tested. To test this hypothesis, experiments were designed to: 1) Quantitate the protein, mRNA and relative occupancy by endogenous steroids of MR and GR, and activity of 11betaHSD in fetal tissues such as lung, kidney, heart, hippocampus, brainstem and pituitary in late gestation fetuses both before and after the time of fetal adrenal maturation (120-140d); 2) Test the effect of blockade of fetal MR receptors on physiologic actions known in the adult to be MR-mediated, renal function and ACTH secretion, and on a possible MR-mediated function in the fetus, lung liquid re-absorption; 3) Test for a relation between MR occupancy and these physiologic effects, and on the proposed target genes for MR action in hippocampus, kidney, and by analogy, fetal lung; 4) to compare the effect of combined MR and GR occupancy on these genes and physiologic actions.