Livingston J N, Lockwood D H
J Biol Chem. 1975 Nov 10;250(21):8353-60.
Glucocorticoids inhibit glucose utilization by fat cells. The possibility that this effect results from altered glucose transport was investigated using an oil-centrifugation technique which allows a rapid (within 45 s) estimation of glucose or 3-O-methylglucose uptake by isolated fat cells. At high concentration (greater than 25 muM), dexamethasone inhibited glucose uptake within 1 min of its addition to fat cells. Efflux of 3-O-methylglucose was also impaired by 0.1 mM dexamethasone. However, diminished glucose uptake was not a specific effect of glucocorticoids; high concentrations (0.1 mM) of 17beta-estradiol, progesterone, and deoxycorticosterone produced a similar response in adipocytes. At a more physiologic steroid concentration (0.1 muM), glucocorticoids inhibited glucose uptake in a time-dependent manner (maximum effect in 1 to 2 hours). This effect was specific for glucocorticoids since, under these conditions, glucose uptake was not changed by the non-glucocorticoid steroids. Lineweaver-Burk analysis showed that 0.1 muM dexamethasone treatment produced a decrease in Vmax for glucose uptake but did not change the Ku. Hexokinase activity and ATP levels were not altered by this treatment, suggesting that processes involved in glucose phosphorylation were not affected. Dexamethasone treatment also caused a reduction in uptake of 3-O-methylglucose when assayed using a low sugar concentration (0.1 mM). At a high concentration (10 mM), uptake of the methyl sugar was only slightly less than normal in treated cells. Stimulation by insulin markedly enhanced uptake of glucose and 3-O-methylglucose by both treated and untreated cells. At a low hexose concentration (0.1 mM) and in the presence of insulin, sugar uptake by dexamethasone-treated cells was slightly less than control cells. Stimulation by insulin did however completely overcome the alteration in hexose uptake when larger concentrations of sugars (greater than 5 mM) were used. There was no detectable change in total protein synthesis during incubation of fat cells with dexamethasone. However, actinomycin C blocked the inhibitory effect of dexamethasone on glucose uptake. Cycloheximide, which caused a small inhibition in glucose uptake, prevented the full expression of the inhibitory effect of dexamethasone on glucose transport. These results indicate that dexamethasone alters the facilitated transport of glucose and, secondly, suggest that synthesis of RNA and protein is needed for glucocorticoid action.
糖皮质激素抑制脂肪细胞对葡萄糖的利用。利用油离心技术研究了这种作用是否由葡萄糖转运改变所致，该技术能快速（45秒内）估算分离的脂肪细胞对葡萄糖或3 - O - 甲基葡萄糖的摄取。在高浓度（大于25μM）时，地塞米松加入脂肪细胞1分钟内就抑制了葡萄糖摄取。0.1 mM地塞米松也损害了3 - O - 甲基葡萄糖的外流。然而，葡萄糖摄取减少并非糖皮质激素的特异性作用；高浓度（0.1 mM）的17β - 雌二醇、孕酮和脱氧皮质酮在脂肪细胞中产生了类似反应。在更生理的类固醇浓度（0.1μM）下，糖皮质激素以时间依赖性方式抑制葡萄糖摄取（1至2小时达到最大效应）。这种作用对糖皮质激素具有特异性，因为在这些条件下，非糖皮质激素类固醇不会改变葡萄糖摄取。Lineweaver - Burk分析表明，0.1μM地塞米松处理使葡萄糖摄取的Vmax降低，但未改变Km。该处理未改变己糖激酶活性和ATP水平，表明参与葡萄糖磷酸化的过程未受影响。用地塞米松处理后，在低糖浓度（0.1 mM）下测定时，3 - O - 甲基葡萄糖摄取也减少。在高浓度（10 mM）时，处理细胞中甲基糖的摄取仅略低于正常水平。胰岛素刺激显著增强了处理和未处理细胞对葡萄糖和3 - O - 甲基葡萄糖的摄取。在低己糖浓度（0.1 mM）且存在胰岛素的情况下，地塞米松处理细胞的糖摄取略低于对照细胞。然而，当使用更高浓度的糖（大于5 mM）时，胰岛素刺激完全克服了己糖摄取的改变。脂肪细胞与地塞米松孵育期间，总蛋白合成未检测到变化。然而，放线菌素C阻断了地塞米松对葡萄糖摄取的抑制作用。环己酰亚胺虽对葡萄糖摄取有轻微抑制作用，但阻止了地塞米松对葡萄糖转运抑制作用的充分表达。这些结果表明，地塞米松改变了葡萄糖的易化转运，其次表明糖皮质激素发挥作用需要RNA和蛋白质的合成。
