Nordeen S K, Young D A
J Biol Chem. 1976 Dec 10;251(23):7295-303.
Inhibition of glucose uptake has been proposed as a primary cause of many of the subsequent inhibitory effects of glucocorticoids. This hypothesis has been tested in experiments where adenosine is substituted for glucose. Like glucose, adenosine maximally supports glycolytic and oxidative ATP generation, and by its use the hormonal inhibition of glucose uptake is circumvented. With adenosine, inhibition by cortisol is seen at at least one other metabolic site, respiratory ATP synthesis. This action can be observed by hormone-induced increases in levels of lactate, pyruvate, and AMP that accompany a lowering of ATP. Evidence for this metabolic action is also seen when cells are provided with a limiting amount of glucose; despite inhibition of glucose uptake, a cortisol-induced increase in lactate accompanies the reduction in levels of ATP. Decreased respiratory ATP synthesis is also suggested by a hormonal reduction in the metabolism of labeled exogenous pyruvate to 14CO2. Several experimental approaches suggest that inhibition of oxidative ATP production, rather than of glucose uptake, is the event most responsible for glucocorticoid-induced changes in the balance of adenine nucleotides, which in turn contribute to effects on protein synthesis and uridine uptake. First, the characteristic inhibitory cortisol effects on adenine nucleotides and protein synthesis are undiminished when adenosine is substituted for glucose. Second, in adenosine-supported cells the onset of the hormone-induced increase in levels of lactate corresponds closely to the appearance of measurable reductions in ATP. In contrast, when cells are supported by glucose, the hormonal inhibition of glucose uptake is maximal by 30 to 35 min, nearly an hour before effects on levels of ATP are detectable. Third, when cells are made strongly dependent upon glucose for ATP production by deprivation of exogenous substrate and cortisol is added at 90 min, a characteristic inhibition of the uptake of glucose added 40 min later is seen; nevertheless, this is insufficient to prevent added glucose from immediately and fully restoring ATP, rates of protein synthesis, and uridine uptake. Inhibitory effects on ATP, protein synthesis, and uridine do appear after an additional hour or so, a time commensurate with the development of an inhibition of oxidative metabolism. Fourth, limiting added glucose can reduce uptake more than cortisol, without reducing levels of ATP.
葡萄糖摄取的抑制被认为是糖皮质激素许多后续抑制作用的主要原因。这一假说已在使用腺苷替代葡萄糖的实验中得到验证。与葡萄糖一样，腺苷能最大程度地支持糖酵解和氧化磷酸化产生ATP，通过使用腺苷可规避激素对葡萄糖摄取的抑制作用。在使用腺苷的情况下，皮质醇的抑制作用至少在另一个代谢位点即呼吸性ATP合成处可见。这种作用可通过激素诱导的乳酸、丙酮酸和AMP水平升高以及ATP水平降低来观察到。当给细胞提供限量的葡萄糖时，也能看到这种代谢作用的证据；尽管葡萄糖摄取受到抑制，但皮质醇诱导的乳酸增加伴随着ATP水平的降低。标记的外源丙酮酸代谢为14CO2的激素性减少也提示呼吸性ATP合成减少。几种实验方法表明，氧化磷酸化产生ATP的抑制而非葡萄糖摄取的抑制，是导致糖皮质激素诱导的腺嘌呤核苷酸平衡变化的主要原因，而腺嘌呤核苷酸平衡变化又进而影响蛋白质合成和尿苷摄取。首先，当用腺苷替代葡萄糖时，皮质醇对腺嘌呤核苷酸和蛋白质合成的特征性抑制作用并未减弱。其次，在由腺苷支持的细胞中，激素诱导的乳酸水平升高的起始时间与可测量到的ATP降低密切相关。相反，当细胞由葡萄糖支持时，激素对葡萄糖摄取的抑制在30至35分钟时达到最大，而此时对ATP水平的影响在近一小时后才可检测到。第三，当通过剥夺外源底物使细胞强烈依赖葡萄糖产生ATP，并在90分钟时添加皮质醇时，会观察到对40分钟后添加的葡萄糖摄取有特征性抑制；然而，这不足以阻止添加的葡萄糖立即并完全恢复ATP、蛋白质合成速率和尿苷摄取。对ATP、蛋白质合成和尿苷的抑制作用在大约一小时后确实会出现，这与氧化代谢抑制的发展时间相符。第四，限制添加的葡萄糖可使摄取的减少超过皮质醇，而不会降低ATP水平。
