山羊肠道内味觉受体（T1R2/T1R3）对不同非结构性碳水化合物源的化学感应机制

Starch is the main component of non-structural carbohydrates in ruminant diets, most of which is fermented and absorbed in the form of volatile fatty acids via rumen microbial fermentation, and only 5 to 20% of which reaches the small intestine and is degraded and absorbed in the form of glucose. As its digestion and absorption in the small intestine in the form of glucose is much more economy than been fermented and absorbed in the form of volatile fatty acids in the rumen, therefore, allowing more starch been digested and absorbed in the small intestine is of great significance to improve feed utilization in ruminant production. Studies have shown that the taste receptor T1R2/T1R3 is widely expressed in the intestine of ruminant animals, indicating that the mechanism of sweet chemosensing mediated by T1R2/T1R3 is likely to be involved in the intestine of ruminants. Currently, research concerning T1R2/T1R3 in the intestine of ruminants has just started, with its signal transduction pathways, nutritional and physiological functions remains unclear yet. We hypothesized that T1R2/T1R3 mediated signaling pathways played an important role in the digestion and utilization of starch in the small intestine of ruminants. Thus, by using goats as experimental animals, we intend to study the mechanism of T1R2/T1R3 mediated glucose chemosensing by immunohistochemistry, immunoprecipitation and laser confocal microscopy; furtherly, the chemosensing mechanism of T1R2/T1R3 for different non-structural carbohydrate sources in the gut of goat will be studied on the basis of using the portal vein catheterization and duodenal fistula perfusion technologies. Through the study of the chemosensing mechanism of T1R2/T1R3 for different non-structural carbohydrate sources in the gut of goat can provide scientific basis for optimizing the regulation of carbohydrate nutrition in diets and improving the utilization of feeds.

淀粉是构成反刍动物日粮中非结构性碳水化合物的主要组分，经瘤胃微生物发酵生成挥发性脂肪酸而被吸收，仅5~20%到达小肠并被降解为葡萄糖吸收。淀粉在小肠内消化吸收的经济性更高，故提高淀粉在小肠内消化吸收比例对提高饲料利用率具有重要意义。研究证实反刍动物肠道内广泛表达了味觉受体T1R2/T1R3，表明反刍动物肠道内可能存在其介导的化学感应机制。当前关于反刍动物肠道内T1R2/T1R3的研究才刚起步，其信号转导路径和营养生理功能尚不明确，但其介导的信号通路对反刍动物小肠内淀粉的消化利用可能具有重要作用。本项目拟以山羊为试验动物，采用免疫组化、免疫共沉淀和激光共聚焦技术，解析T1R2/T1R3介导的葡萄糖感应机制；并基于肝门静脉插管和十二指肠瘘管技术，研究T1R2/T1R3对不同非结构性碳水化合物源的感应机制。旨在为优化反刍家畜日粮碳水化合物营养调控和有效提高饲料利用率提供科学依据。

淀粉是构成反刍动物日粮中非结构性碳水化合物的主要组分，其在小肠内消化吸收的经济性更高，故提高淀粉在小肠内消化吸收比例对提高反刍动物饲料利用率具有重要意义。由于糖苷键连接方式的不同，淀粉可分为直链淀粉和支链淀粉，二者结构的差异性使得它们在反刍动物体内的降解速率与降解部位存在差异，相对于支链淀粉，直链淀粉在瘤胃中的消化降解速率更慢，能更多的进入小肠内进行消化吸收。研究证实反刍动物肠道内广泛表达了味觉受体T1R2/T1R3，表明反刍动物肠道内可能存在其介导的化学感应机制。通过分别开展三个动物试验，对甜味受体T1R2/T1R3 及信号通路元件的组织表达及日粮直链/支链淀粉比对和日粮淀粉水平对山羊肠道肠甜味受体及信号通路关键元件和氨基酸代谢的影响进行了测定。结果发现：1）甜味受体亚基T1R2和T1R3及其信号通路关键元件TRPM5和Gα-gustducin在山羊小肠中在mRNA和蛋白水平均有表达，表明甜味受体介导的葡萄糖感应机制广泛存在于山羊小肠内；2）高直玉米替代普通玉米对断奶羔羊的生长发育具有积极影响，能提高营养物质的消化率，促进能量饲料的有效利用，促进氨基酸代谢和肌肉中蛋白质的沉积；3）空肠和回肠内葡萄糖浓度与甜味受体及其通路元件 (T1R3、Gα-gustducin、TRPM5、GLUT2和SGLT1) 之间存在正相关关系，但是日粮淀粉水平对肠道甜味受体的表达影响较小。

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