Department of Anatomy, Cell Biology and Physiology, American University of Beirut, P.O. Box 113-6044, Beirut, Lebanon.
Department of Internal Medicine, American University of Beirut Medical Center, P.O. Box 113-6044, Hamra, Beirut, 110-32090, Lebanon.
Pflugers Arch. 2019 Apr;471(4):595-603. doi: 10.1007/s00424-018-2230-0. Epub 2018 Nov 6.
Nutrients in the lumen of the small intestine are sensed by special cells in the epithelial lining. The ensuing neurohumoral reflexes affect gastrointestinal absorption/secretion, motility, and vascular perfusion. To study in vivo the effect of a monosaccharide (glucose) or polysaccharide (starch) present in the jejunum on glucose absorption from an adjacent part of the intestine and investigate the possible underlying mechanisms. Using the single pass intraluminal perfusion technique, a segment of jejunum (perfusion segment) was continuously perfused with 20 mM glucose to determine glucose absorption. One hour later, a bolus of a saccharide was instilled in an isolated adjacent jejunal segment and the change in glucose absorption was monitored for a further 2 h. The contribution of neural mechanisms in this process was investigated. Instillation of glucose (20 mM or 40 mM) in either distal or proximal jejunal pouch elicited immediate and sustained inhibition of glucose absorption (a decrease by 25%; P < 0.01) from the perfused jejunal segment. Comparable inhibition was obtained with instillation of other monosaccharides or starch in the jejunal pouch. This inhibition was abolished by adding tetrodotoxin to the pouch or to the perfused jejunal segment and also by pretreatment with sympathetic blockers (guanethidine or hexamethonium) and by chemical ablation of capsaicin-sensitive primary afferent fibers. Glucose absorption within the jejunum is auto-regulated through backward and forward mechanisms. This regulation is mediated by neural reflexes involving capsaicin-sensitive afferent and sympathetic efferent fibers. These reflexes might serve to protect against hyperglycemia.
小肠腔中的营养素被上皮衬里中的特殊细胞感知。随之而来的神经激素反射会影响胃肠道的吸收/分泌、运动和血管灌注。本研究旨在体内研究存在于空肠中的单糖（葡萄糖）或多糖（淀粉）对相邻肠段葡萄糖吸收的影响，并探讨可能的潜在机制。使用单次肠腔内灌注技术，连续用 20mM 葡萄糖灌注一段空肠（灌注段）以确定葡萄糖吸收。1 小时后，将糖溶液团块注入相邻的空肠段，进一步监测 2 小时内葡萄糖吸收的变化。研究了这个过程中神经机制的作用。在远端或近端空肠囊中注入葡萄糖（20mM 或 40mM）会立即和持续抑制从灌注的空肠段吸收葡萄糖（减少 25%；P<0.01）。在空肠囊中注入其他单糖或淀粉也会产生类似的抑制作用。向囊中或灌注的空肠段中加入河豚毒素、用交感神经阻滞剂（胍乙啶或六烃季铵）预处理以及用辣椒素敏感的初级传入纤维化学消融也可以消除这种抑制作用。空肠中的葡萄糖吸收通过前后机制进行自动调节。这种调节是通过涉及辣椒素敏感传入和交感传出纤维的神经反射来介导的。这些反射可能有助于防止高血糖。
