Houghton Scott G, Iqbal Corey W, Duenes Judith A, Fatima Javairiah, Kasparek Michael S, Sarr Michael G
Department of Surgery, GI Research Unit, Alfred 2, St Mary's Hospital, Mayo Clinic College of Medicine, Rochester, Minn 55905, USA.
Surgery. 2008 Jan;143(1):79-93. doi: 10.1016/j.surg.2007.06.007. Epub 2007 Dec 3.
Hexose transporter mRNA and protein levels follow a diurnal rhythm in rat jejunum. Their coordinated expression and resultant function throughout the small bowel is not well understood. We hypothesized that hexose transporter levels and glucose absorption follow a coordinated, site-specific diurnal rhythm in rat duodenum and jejunum, but not in ileum.
Sprague-Dawley rats were housed in a strictly maintained, 12-h, light/dark room [light 6 am to 6 pm] with free access to water and chow. Mucosa was harvested from duodenum, jejunum, and ileum at 3 am, 9 am, 3 pm, and 9 pm, and full thickness 1-cm segments were harvested at 9 am, and 9 pm (n = 6 for each segment at each time point). mRNA levels were determined by reverse-transcription, real-time polymerase chain reaction (n > or = 5), protein levels by semiquantitative Western blotting (n > or = 5), and transporter-mediated glucose uptake by everted sleeve technique (n = 6).
mRNA levels of SGLT1 and GLUT5 followed a temporally coordinated, diurnal rhythm in all 3 segments (P < .01), while mRNA for GLUT2 and protein levels for SGLT1 and GLUT2 varied diurnally only in duodenum and jejunum (P > .05) but not in ileum (P > .10). SGLT1 and GLUT5 mRNA induction decreased aborally. Baseline SGLT1 and GLUT5 mRNA levels and SLGT1 and GLUT2 protein levels did not vary aborally (P > .05 for all). GLUT2 mRNA baseline levels were decreased in ileum (P < .01). Glucose uptake varied diurnally in duodenum and jejunum with no difference in ileum. Transporter-mediated glucose uptake was greater in duodenum and jejunum compared with ileum.
Regulation of hexose absorption in rat small bowel seems to be site-specific and mediated by multiple mechanisms.
己糖转运蛋白的mRNA和蛋白质水平在大鼠空肠中呈现昼夜节律。其在整个小肠中的协同表达及由此产生的功能尚未完全明确。我们推测，己糖转运蛋白水平和葡萄糖吸收在大鼠十二指肠和空肠中遵循协同的、位点特异性的昼夜节律，而在回肠中则不然。
将Sprague-Dawley大鼠饲养在严格维持12小时光照/黑暗周期（上午6点至下午6点为光照）的房间内，自由饮水和进食。在凌晨3点、上午9点、下午3点和晚上9点从十二指肠、空肠和回肠采集黏膜，在上午9点和晚上9点采集1厘米厚的全层肠段（每个时间点每个肠段n = 6）。通过逆转录实时聚合酶链反应测定mRNA水平（n≥5），通过半定量蛋白质印迹法测定蛋白质水平（n≥5），并通过外翻肠囊技术测定转运蛋白介导的葡萄糖摄取（n = 6）。
SGLT1和GLUT5的mRNA水平在所有3个肠段中均呈现时间上协同的昼夜节律（P <.01），而GLUT2的mRNA以及SGLT1和GLUT2的蛋白质水平仅在十二指肠和空肠中呈现昼夜变化（P>.05），在回肠中无变化（P>.10）。SGLT1和GLUT5的mRNA诱导向口侧降低。SGLT1和GLUT5的mRNA基线水平以及SLGT1和GLUT2的蛋白质水平向口侧无变化（所有P>.05）。回肠中GLUT2的mRNA基线水平降低（P <.01）。葡萄糖摄取在十二指肠和空肠中呈现昼夜变化，在回肠中无差异。与回肠相比，十二指肠和空肠中转运蛋白介导的葡萄糖摄取更高。
大鼠小肠中己糖吸收的调节似乎是位点特异性的，并且由多种机制介导。
