Corpe C P, Burant C F
Department of Medicine, University of Chicago, Illinois 60637, USA.
Am J Physiol. 1996 Jul;271(1 Pt 1):G211-6. doi: 10.1152/ajpgi.1996.271.1.G211.
In rodents, a number of intestinal digestive and absorptive processes demonstrate a diurnal pattern of activity. To investigate if the jejunal hexose transporters are regulated in such a diurnal fashion, the levels for the glucose and fructose transporter mRNA and proteins were determined at 6-h intervals over a 24-h control fed period. SGLT-1, GLUT-2, and GLUT-5 mRNA levels increased between two- and eightfold before the onset of peak feeding. GLUT-5 protein levels also varied in a diurnal fashion but were out of phase with the observed changes in GLUT-5 mRNA levels. In contrast, GLUT-2 protein levels remained relatively constant during the control fed 24-h period. The effect of dietary manipulations on the observed diurnal variation was also investigated. After only 3 h of feeding a 60% fructose-enriched diet, the levels of GLUT-5 mRNA and protein were significantly elevated. GLUT-5 mRNA and protein levels remained elevated relative to the level of control diet-fed animals over the ensuing 24 h and during the 7th day of fructose feeding. Exposure to elevated levels of fructose had no significant effect on the diurnal pattern of GLUT-2 and SGLT-1 mRNA. In contrast, GLUT-2 protein was rapidly downregulated during the length of the fructose feeding study. In conclusion, the data demonstrate a normal daily variation in the level of hexose transporter expression that can be rapidly modulated by diet.
在啮齿动物中，许多肠道消化和吸收过程呈现出昼夜活动模式。为了研究空肠己糖转运蛋白是否以这种昼夜方式受到调节，在24小时对照喂养期间，每隔6小时测定一次葡萄糖和果糖转运蛋白的mRNA和蛋白质水平。在进食高峰开始前，SGLT-1、GLUT-2和GLUT-5的mRNA水平增加了两到八倍。GLUT-5蛋白水平也呈现昼夜变化，但与GLUT-5 mRNA水平的变化不同步。相比之下，在对照喂养的24小时期间，GLUT-2蛋白水平保持相对恒定。还研究了饮食操作对观察到的昼夜变化的影响。在喂食富含60%果糖的饮食仅3小时后，GLUT-5 mRNA和蛋白水平显著升高。在随后的24小时以及果糖喂养的第7天，相对于对照饮食喂养动物的水平，GLUT-5 mRNA和蛋白水平持续升高。果糖水平升高对GLUT-2和SGLT-1 mRNA的昼夜模式没有显著影响。相比之下，在果糖喂养研究期间，GLUT-2蛋白迅速下调。总之，数据表明己糖转运蛋白表达水平存在正常的每日变化，且可被饮食快速调节。
