Myers D A, Myers T R, Grober M S, Nathanielsz P W
Laboratory for Pregnancy and Newborn Research, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401.
Endocrinology. 1993 May;132(5):2109-16. doi: 10.1210/endo.132.5.8386607.
CRH regulates POMC gene expression and subsequent ACTH biosynthesis and release. In sheep, the preterm rise in fetal plasma ACTH commences at approximately 125 days gestation (dGA; 147 dGA = term), preceding the initiation of adrenocortical steroidogenesis. We hypothesized that an increase in CRH expression in the hypothalamic paraventricular nucleus (PVN) and POMC expression in the anterior pituitary in the late gestation sheep fetus may precede adrenal cortex maturation. Fetal sheep were obtained at 105-107 (n = 4), 128-130 (n = 5), and 138-140 (n = 4) dGA. Hypothalami were cryosectioned and subjected to in situ hybridization for ovine CRH mRNA. In all dGA groups, expression of CRH mRNA was observed throughout the rostrocaudal extent of the fetal PVN. The midrostral region of the fetal PVN where the dorsal and ventral divisions of the rostral PVN merge to form a single structure was selected for quantification. The number of copies of CRH probe hybridized per micron 3 were determined to estimate the quantity of hybridized CRH mRNA; the mean estimated CRH mRNA copy number per micron 3 midrostral PVN were 0.064 +/- 0.012 (105-107 dGA), 0.237 +/- 0.048 (128-130 dGA), and 0.108 +/- 0.034 (138-140 dGA; mean +/- SEM copies per micron 3 PVN). CRH mRNA signal significantly increased between 105-107 and 128-130 dGA (P < or = 0.05); 138-140 dGA levels of mRNA were not different from either 105-107 or 128-140 dGA levels. Regional variation in CRH mRNA levels were observed within the midrostral PVN between groups; at 138-140 dGA, a population of lateral midrostral PVN neurons maintain CRH mRNA levels greater than 105-107 dGA (P < 0.05), similar to those at 128-130 dGA. Fetal anterior pituitary RNA was subjected to Northern analysis for POMC mRNA. POMC mRNA levels in fetal anterior pituitaries were 14.1 +/- 2.2 (105-107 dGA), 28.9 +/- 10.9 (128-130 dGA), and 43.2 +/- 6 (138-140 dGA; mean +/- SEM arbitrary units). A significant increase (P < or = 0.05) was observed at 138-140 dGA compared to levels at 105-107 dGA. We conclude CRH mRNA levels in the fetal PVN increase coincident with increased POMC gene expression and the late gestation rise in fetal plasma ACTH. We speculate that a neuroendocrine stimulus at the fetal PVN may precipitate increased levels of CRH mRNA, initiating the maturation of the fetal hypothalamic-hypophyseal-adrenal axis, thus inducing the events of labor and delivery in sheep.
促肾上腺皮质激素释放激素（CRH）调节阿黑皮素原（POMC）基因表达以及随后的促肾上腺皮质激素（ACTH）生物合成与释放。在绵羊中，胎儿血浆ACTH在妊娠约125天（妊娠天数，dGA；足月为147 dGA）时开始出现早产时的升高，早于肾上腺皮质类固醇生成的启动。我们假设，妊娠晚期绵羊胎儿下丘脑室旁核（PVN）中CRH表达的增加以及垂体前叶中POMC表达的增加可能先于肾上腺皮质成熟。在105 - 107天（n = 4）、128 - 130天（n = 5）和138 - 140天（n = 4）dGA获取胎羊。将下丘脑进行冷冻切片，并进行绵羊CRH mRNA的原位杂交。在所有dGA组中，在胎儿PVN的整个 rostrocaudal范围内均观察到CRH mRNA的表达。选择胎儿PVN的中吻部区域进行定量，该区域是吻侧PVN的背侧和腹侧部分融合形成单一结构的地方。确定每立方微米杂交的CRH探针拷贝数，以估计杂交的CRH mRNA的量；中吻部PVN每立方微米的平均估计CRH mRNA拷贝数分别为0.064 ± 0.012（105 - 107 dGA）、0.237 ± 0.048（128 - 130 dGA）和0.108 ± 0.034（138 - 140 dGA；每立方微米PVN的平均 ± 标准误拷贝数）。CRH mRNA信号在105 - 107天和128 - 130天之间显著增加（P≤0.05）；138 - 140天的mRNA水平与105 - 107天或128 - 140天的水平无差异。在各中吻部PVN组之间观察到CRH mRNA水平的区域差异；在138 - 140天，中吻部PVN外侧的一群神经元维持的CRH mRNA水平高于105 - 107天（P < 0.05），与128 - 130天的水平相似。对胎儿垂体前叶RNA进行POMC mRNA的Northern分析。胎儿垂体前叶中POMC mRNA水平分别为14.1 ± 2.2（105 - 107 dGA）、28.9 ± 10.9（128 - 130 dGA）和43.2 ± （138 - 140 dGA；平均 ± 标准误任意单位）。与105 - 107天的水平相比，在138 - 140天观察到显著增加（P≤0.05）。我们得出结论，胎儿PVN中CRH mRNA水平的增加与POMC基因表达的增加以及妊娠晚期胎儿血浆ACTH的升高同时发生。我们推测，胎儿PVN处的神经内分泌刺激可能促使CRH mRNA水平升高，启动胎儿下丘脑 - 垂体 - 肾上腺轴的成熟，从而引发绵羊的分娩事件。
