Sarantos P, Howard D, Souba W W
Department of Surgery, Physiology, University of Florida College of Medicine, Gainesville.
Metabolism. 1993 Jun;42(6):795-800. doi: 10.1016/0026-0495(93)90252-j.
Since the lungs play a central role in maintaining glutamine homeostasis in normal and catabolic disease states, we studied the regulation of glutamine synthetase (GS) expression by dexamethasone in rat lung. Adult rats received saline (controls) or dexamethasone (0.5 mg/kg). Lung total RNA was extracted for Northern hybridization and labeled with an alpha-32P rat GS cDNA probe. The mRNA of the constitutively expressed gene beta-actin was the control for RNA loading. GS transcripts were measured by laser densitometry and normalized to actin, and GS specific activity was also determined. Following a single injection of dexamethasone (0.5 mg/kg), lung GS activity increased by 40% at 4 hours and by 75% at 8 hours. The dexamethasone-mediated increase in GS activity was associated with a marked increase in GS mRNA levels, which preceded the increase in enzyme activity by approximately 2 hours. Serial daily dexamethasone administration for 3 and 6 days caused an even greater increase in GS mRNA levels and specific activity. No effect was seen on beta-actin levels, demonstrating that the expression of GS was not part of a global response to steroids. Therefore, glucocorticoids stimulate GS expression in rat lung. This regulation appears to be one mechanism by which lung glutamine release is augmented during critical illness.
由于肺在维持正常和分解代谢疾病状态下的谷氨酰胺稳态中起核心作用，我们研究了地塞米松对大鼠肺中谷氨酰胺合成酶（GS）表达的调控。成年大鼠接受生理盐水（对照组）或地塞米松（0.5mg/kg）处理。提取肺总RNA用于Northern杂交，并用α-32P大鼠GS cDNA探针进行标记。组成型表达基因β-肌动蛋白的mRNA作为RNA上样量的对照。通过激光密度测定法测量GS转录本，并将其与肌动蛋白进行标准化，同时还测定了GS的比活性。单次注射地塞米松（0.5mg/kg）后，肺GS活性在4小时时增加了40%，在8小时时增加了75%。地塞米松介导的GS活性增加与GS mRNA水平的显著增加相关，GS mRNA水平的增加比酶活性的增加提前约2小时。连续3天和6天每日给予地塞米松导致GS mRNA水平和比活性进一步增加。对β-肌动蛋白水平未见影响，表明GS的表达不是对类固醇的整体反应的一部分。因此，糖皮质激素刺激大鼠肺中GS的表达。这种调控似乎是危重病期间肺谷氨酰胺释放增加的一种机制。
