Wardlaw S L, McCarthy K C, Conwell I M
Department of Medicine, Columbia University College of Physicians & Surgeons, New York, NY 10032, USA.
Neuroendocrinology. 1998 Jan;67(1):51-7. doi: 10.1159/000054298.
Although glucocorticoids clearly inhibit proopiomelanocortin (POMC) gene transcription and peptide synthesis in the anterior pituitary, the effects of glucocorticoids on POMC in the hypothalamus are still unclear, even though most POMC neurons in the arcuate nucleus are known to have glucocorticoid receptors. In this study, we have therefore examined the effect of adrenalectomy (ADX) and glucocorticoid replacement on POMC mRNA and peptide (beta-EP and alpha-MSH) levels in the medial basal hypothalamus (MBH) of the rat. POMC mRNA was measured by a sensitive solution hybridization S1 nuclease protection assay, and beta-EP and alpha-MSH were measured by radioimmunoassay. In a first experiment, animals were studied 7 days after ADX or sham surgery. The mean POMC mRNA concentration was 1.01+/-0.14 pg/microg RNA (means+/-SE) in the intact animals and decreased to 0.55+/-0.07 pg/microg RNA in the MBH of the ADX animals (p < 0.005). Beta-EP levels decreased in parallel from 4.30+/-0.18 to 3.36+/-0.11 ng/mg protein (p < 0.001); alpha-MSH levels decreased from 3.25+/-0.21 to 2.41+/-0.16 ng/mg protein (p < 0.005). In a second experiment, animals were studied 2 weeks after ADX. POMC mRNA levels again fell significantly from 1.15+/-0.19 pg/microg RNA in the intact animals to 0.51+/-0.06 pg/microg in the ADX animals (p < 0.01). Beta-EP levels fell also, but this was not significant. In a third experiment, all animals underwent ADX, and half of them received daily subcutaneous injections of dexamethasone (20 microg). Nine days after ADX, the mean POMC mRNA level was 0.66+/-0.04 pg/microg RNA in the saline-treated animals and increased to 0.98+/-0.08 pg/microg RNA in the dexamethasone-treated animals (p < 0.005). A parallel increase in beta-EP levels from 5.03+/-0.41 to 6.01+/-0.53 ng/mg protein was also noted, but this was not statistically significant. We conclude that POMC gene expression is significantly inhibited in the MBH at 1 and 2 weeks after ADX. This effect was reversed by glucocorticoid replacement with doses close to the physiological range. The parallel changes in POMC mRNA and peptide levels strongly suggest that, in contrast to the anterior pituitary, low doses of glucocorticoids stimulate the biosynthesis of POMC in the MBH of ADX rats.
虽然糖皮质激素明显抑制垂体前叶中阿片促黑皮质素原（POMC）基因转录和肽合成，但糖皮质激素对下丘脑POMC的影响仍不清楚，尽管已知弓状核中的大多数POMC神经元都有糖皮质激素受体。因此，在本研究中，我们检测了肾上腺切除术（ADX）和糖皮质激素替代对大鼠内侧基底下丘脑（MBH）中POMC mRNA和肽（β - 内啡肽和α - 促黑素）水平的影响。通过灵敏的溶液杂交S1核酸酶保护试验检测POMC mRNA，通过放射免疫分析法检测β - 内啡肽和α - 促黑素。在第一个实验中，对ADX或假手术后7天的动物进行研究。完整动物的MBH中POMC mRNA平均浓度为1.01±0.14 pg/μg RNA（平均值±标准误），ADX动物的MBH中该浓度降至0.55±0.07 pg/μg RNA（p < 0.005）。β - 内啡肽水平平行下降，从4.30±0.18降至3.36±0.11 ng/mg蛋白质（p < 0.001）；α - 促黑素水平从3.25±0.21降至2.41±0.16 ng/mg蛋白质（p < 0.005）。在第二个实验中，对ADX后2周的动物进行研究。POMC mRNA水平再次显著下降，从完整动物的1.15±0.19 pg/μg RNA降至ADX动物的0.51±0.06 pg/μg（p < 0.01）。β - 内啡肽水平也下降，但不显著。在第三个实验中，所有动物均接受ADX，其中一半动物每天皮下注射地塞米松（20 μg）。ADX后9天，生理盐水处理动物的POMC mRNA平均水平为0.66±0.04 pg/μg RNA，地塞米松处理动物的该水平升至0.98±0.08 pg/μg RNA（p < 0.005）。还观察到β - 内啡肽水平从5.03±0.41平行升至6.01±0.53 ng/mg蛋白质，但无统计学意义。我们得出结论，ADX后1周和2周时，MBH中POMC基因表达受到显著抑制。用接近生理范围的剂量进行糖皮质激素替代可逆转这种作用。POMC mRNA和肽水平的平行变化强烈表明，与垂体前叶相反，低剂量糖皮质激素刺激ADX大鼠MBH中POMC的生物合成。
