Leibniz Institute for Farm Animal Biology (FBN), Dummerstorf, Germany.
J Dairy Sci. 2011 Sep;94(9):4546-55. doi: 10.3168/jds.2011-4333.
Diets containing corn starch may improve glucose supply by providing significant amounts of intestinal starch and increasing intestinal glucose absorption in dairy cows. Glucose absorption in the small intestine requires specific glucose transporters; that is, sodium-dependent glucose co-transporter-1 (SGLT1) and facilitated glucose transporter (GLUT2), which are usually downregulated in the small intestine of functional ruminants but are upregulated when luminal glucose is available. We tested the hypothesis that mRNA and protein expression of intestinal glucose transporters and mRNA expression of enzymes related to gluconeogenesis are affected by variable starch supply. Dairy cows (n=9/group) were fed for 4 wk total mixed rations (TMR) containing either high (HS) or low (LS) starch levels in the diet. Feed intake and milk yield were measured daily. After slaughter, tissue samples of the small intestinal mucosa (mid-duodenum and mid-jejunum) were taken for determination of mRNA concentrations of SGLT1 and GLUT2 as well as pyruvate carboxylase, cytosolic phosphoenolpyruvate carboxykinase, and glucose-6-phosphatase by real-time reverse transcription PCR relative to a housekeeping gene. Protein expression of GLUT2 in crude mucosal membranes and of SGLT1 and GLUT2 in brush-border membrane vesicles was quantified by sodium dodecyl sulfate-PAGE and immunoblot. A mixed model was used to examine feeding and time-related changes on feed intake and milk yield and to test feeding and gut site effects on gene or protein expression of glucose transporters and enzymes in the intestinal mucosa. Dry matter intake, but not energy intake, was higher in cows fed HS compared with LS. Abundance of SGLT1 mRNA tended to be higher in duodenal than in jejunal mucosa, and mRNA abundances of pyruvate carboxylase tended to be higher in jejunal than in duodenal mucosa. In brush-border membrane vesicles, SGLT1 and GLUT2 protein expression could be demonstrated. No diet-dependent differences were found concerning mRNA and protein contents of glucose transporter or mRNA level of gluconeogenic enzymes. In conclusion, our investigations on glucose transporters and gluconeogenic enzymes in the small intestinal mucosa of dairy cows did not show significant diet regulation when TMR with different amounts of intestinal starch were fed. Therefore, predicted intestinal glucose absorption after enhanced starch feeding is probably not supported by changes of intestinal glucose transporters in dairy cows.
含有玉米淀粉的日粮可以通过提供大量肠道淀粉并增加奶牛肠道葡萄糖吸收来改善葡萄糖供应。小肠中的葡萄糖吸收需要特定的葡萄糖转运蛋白，即钠依赖性葡萄糖协同转运蛋白-1（SGLT1）和易化葡萄糖转运蛋白（GLUT2），它们在功能性反刍动物的小肠中通常下调，但在肠腔葡萄糖可用时上调。我们测试了以下假设：肠道葡萄糖转运体的 mRNA 和蛋白表达以及与糖异生相关的酶的 mRNA 表达受可变淀粉供应的影响。奶牛（n=9/组）用含有高（HS）或低（LS）淀粉水平的全混合日粮（TMR）喂养 4 周。每日测量采食量和产奶量。屠宰后，从小肠黏膜（十二指肠和空肠中部）中取出组织样本，通过实时逆转录 PCR 相对于管家基因测定 SGLT1 和 GLUT2 以及丙酮酸羧激酶、胞质磷酸烯醇丙酮酸羧激酶和葡萄糖-6-磷酸酶的 mRNA 浓度。用十二烷基硫酸钠-PAGE 和免疫印迹法定量粗粘膜膜中的 GLUT2 蛋白表达以及刷状缘膜囊泡中的 SGLT1 和 GLUT2 蛋白表达。使用混合模型检查采食和时间相关变化对采食量和产奶量的影响，并检验采食和肠道部位对葡萄糖转运体和肠道黏膜中酶基因或蛋白表达的影响。与 LS 相比，HS 组奶牛的干物质采食量更高，但能量摄入量没有差异。SGLT1 mRNA 的丰度在十二指肠黏膜中高于空肠黏膜，而丙酮酸羧激酶的 mRNA 丰度在空肠黏膜中高于十二指肠黏膜。在刷状缘膜囊泡中，可以证明 SGLT1 和 GLUT2 蛋白的表达。关于葡萄糖转运体或糖异生酶的 mRNA 水平，没有发现日粮相关差异。因此，当饲喂含有不同数量肠道淀粉的 TMR 时，我们对奶牛小肠黏膜中葡萄糖转运体和糖异生酶的研究没有显示出明显的饮食调节。因此，在增强淀粉喂养后预测的肠道葡萄糖吸收可能不支持奶牛肠道葡萄糖转运体的变化。
