Nambi P, Pullen M, Wu H L, Nuthulaganti P, Elshourbagy N, Kumar C
Department of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406-0939.
J Biol Chem. 1992 Sep 25;267(27):19555-9.
Steroid hormones have been shown to modulate a number of physiological processes in addition to their potent antiinflammatory effects. Endothelin (ET) is a newly discovered vasoconstrictor that is synthesized and released by endothelial cells and acts on adjacent vascular smooth muscle cells by interacting with specific cell surface receptors. Proinflammatory agents such as thrombin and transforming growth factor beta have been shown to up-regulate ET gene expression in vascular endothelial cells. We wondered whether the anti-inflammatory steroids might have any regulatory effect on the ET receptors present in the vascular smooth muscle cells. Rat vascular smooth muscle cells (A-10 cell line, ATCC.CRL 1476) were used as a model system to study the effects of glucocorticoids on ET receptor expression and function. These cells display high density and high affinity ET receptors that belong to the ETA subtype. Pretreatment of these cells with dexamethasone reduced the number of ET receptors by 50-60% without changing the affinity. Of the steroids tested, dexamethasone was most effective followed by prednisolone and hydrocortisone. Aldosterone, a mineralocorticoid, was 5000-fold less potent than dexamethasone. This effect of dexamethasone was dependent on the time of pretreatment and concentration of the steroid used. This down-regulation of ET receptors was also accompanied by an attenuated response to ET-1 in dexamethasone-pretreated cells. The inhibitory effect of dexamethasone was selective for ET receptors because the vasopressin-mediated response was unaffected. In addition, dexamethasone pretreatment of these cells resulted in 50-60% reduction in the steady-state level of ETA receptor mRNA as revealed by Northern analysis. These results suggest that glucocorticoid pretreatment of smooth muscle cells resulted in the down-regulation of the ETA receptor at the mRNA level.
除了具有强大的抗炎作用外，类固醇激素还被证明可调节多种生理过程。内皮素（ET）是一种新发现的血管收缩剂，由内皮细胞合成并释放，通过与特定细胞表面受体相互作用作用于相邻的血管平滑肌细胞。凝血酶和转化生长因子β等促炎剂已被证明可上调血管内皮细胞中ET基因的表达。我们想知道抗炎类固醇是否可能对血管平滑肌细胞中存在的ET受体有任何调节作用。大鼠血管平滑肌细胞（A-10细胞系，ATCC.CRL 1476）被用作模型系统，以研究糖皮质激素对ET受体表达和功能的影响。这些细胞显示出高密度和高亲和力的ET受体，属于ETA亚型。用地塞米松预处理这些细胞可使ET受体数量减少50-60%，而不改变亲和力。在所测试的类固醇中，地塞米松最有效，其次是泼尼松龙和氢化可的松。盐皮质激素醛固酮的效力比地塞米松低5000倍。地塞米松的这种作用取决于预处理时间和所用类固醇的浓度。地塞米松预处理细胞后，ET受体的下调还伴随着对ET-1反应的减弱。地塞米松的抑制作用对ET受体具有选择性，因为血管加压素介导的反应不受影响。此外，如Northern分析所示，用地塞米松预处理这些细胞导致ETA受体mRNA的稳态水平降低50-60%。这些结果表明，糖皮质激素预处理平滑肌细胞导致ETA受体在mRNA水平下调。
