Yang Z, Lee D, Huang W, Copolov D L, Lim A T
Cell Biology Unit, Mental Health Research Institute of Victoria, Royal Park Hospital, Parkville, Australia.
Brain Res. 1994 Jun 13;648(1):99-108. doi: 10.1016/0006-8993(94)91910-0.
Beta-endorphin(beta EP)1-31, a potent opioid peptide of proopiomelanocortin (POMC) derivatives, is produced and released from neurons at arcuate nuclei of the rat hypothalamus. Although dexamethasone (DM) suppresses the production and secretion of POMC related peptides from rat pituitary corticotrophs, the effect of glucocorticoids on the function of hypothalamic beta EP neurons remains unclear. Employing long term monolayer cultures of neonatal rat hypothalamic cells, we report here that 4 day treatment with 10 microM of forskolin increased ir-beta EP levels in cell content and culture media by approximately 1.7 (P < 0.05) and 4.1 times (P < 0.01) above vehicle treated control cultures (mean +/- S.E.M., 47.3 +/- 2.6 pg/well and 40.4 +/- 3.0 pg/well; n = 3) respectively. Although 4 day treatment with DM alone had little effect on the release and the cell content of ir-beta EP, it significantly enhanced forskolin-induced elevation of ir-beta EP levels in cell content and in culture media. The effect of DM was dose-related and time-dependent, with an EC50 of about 1 nM; at this concentration DM enhanced ir-beta EP secretion about 2.1 times (P < 0.01) above that induced by 10 microM of forskolin alone. Furthermore, the potentiating effect of DM was specifically suppressed by 100 nM of RU38486 (P < 0.01), a glucocorticoid receptor antagonist, but not by an equivalent dose of RU28318, a mineralocorticoid receptor antagonist. In addition, Northern blot analysis showed that forskolin (10 microM) increased the abundance of POMC mRNA 1.4 fold above that of vehicle treated control cultures. Whereas by itself, DM (10 nM) had little effect on the level of POMC mRNA, it enhanced forskolin-stimulated increase of the abundance of POMC mRNA approximately 2.6 times. Moreover, DM also augmented 1.6 times (P < 0.05) forskolin-induced but not 3-isobutyl-1-methylxanthine (IBMX)-induced increase of cAMP production (5.5 +/- 0.4 pmol/well; mean +/- S.E.M., n = 3) in the cultures. Taken together, our findings suggest that in contrast to the inhibitory effect on pituitary corticotrophs, glucocorticoids enhance the production and secretion of beta EP from rat hypothalamic neurons by facilitating the stimulatory effect mediated, in part, through the adenylyl cyclase-cAMP system.
β-内啡肽（β-EP）1-31是促阿片黑素细胞皮质素（POMC）衍生物中的一种强效阿片肽，由大鼠下丘脑弓状核的神经元产生并释放。虽然地塞米松（DM）可抑制大鼠垂体促肾上腺皮质激素细胞中POMC相关肽的产生和分泌，但糖皮质激素对下丘脑β-EP神经元功能的影响仍不清楚。利用新生大鼠下丘脑细胞的长期单层培养，我们在此报告，用10μM福司可林处理4天，可使细胞内容物和培养基中的免疫反应性β-EP（ir-β-EP）水平分别比用载体处理的对照培养物升高约1.7倍（P<0.05）和4.1倍（P<0.01）（平均值±标准误，分别为47.3±2.6 pg/孔和40.4±3.0 pg/孔；n=3）。虽然单独用DM处理4天对ir-β-EP的释放和细胞内容物影响不大，但它显著增强了福司可林诱导的细胞内容物和培养基中ir-β-EP水平的升高。DM的作用呈剂量依赖性和时间依赖性，半数有效浓度（EC50）约为1 nM；在此浓度下，DM使ir-β-EP分泌比单独用10μM福司可林诱导的水平提高约2.1倍（P<0.01）。此外，糖皮质激素受体拮抗剂100 nM的RU38486可特异性抑制DM的增强作用（P<0.01），而盐皮质激素受体拮抗剂等量的RU28318则无此作用。另外，Northern印迹分析表明，福司可林（10μM）使POMC mRNA丰度比用载体处理的对照培养物增加1.4倍。而DM（10 nM）本身对POMC mRNA水平影响不大，但它使福司可林刺激的POMC mRNA丰度增加约2.6倍。此外，DM还使培养物中福司可林诱导的而非3-异丁基-1-甲基黄嘌呤（IBMX）诱导的环磷酸腺苷（cAMP）生成增加1.6倍（P<0.05）（5.5±0.4 pmol/孔；平均值±标准误，n=3）。综上所述，我们的研究结果表明，与对垂体促肾上腺皮质激素细胞的抑制作用相反，糖皮质激素通过促进部分由腺苷酸环化酶-cAMP系统介导的刺激作用，增强大鼠下丘脑神经元β-EP的产生和分泌。
