Laforenza U, Patrini C, Alvisi C, Faelli A, Licandro A, Rindi G
Institute of Human Physiology, University of Pavia, Italy.
Am J Clin Nutr. 1997 Aug;66(2):320-6. doi: 10.1093/ajcn/66.2.320.
Mucosal biopsy specimens obtained by routine endoscopy from 108 human subjects, including one patient with thiamine deficiency, were incubated at 37 degrees C in oxygenated calcium-free Krebs-Ringer solution (pH 7.5) containing tritiated thiamine and [14C]dextran as a marker of adherent mucosal water. The amount of labeled thiamine taken up was measured radiometrically. In subjects with no clinical evidence of thiamine deficiency, 1) thiamine uptake by duodenal mucosa had a hyperbolic time course, reaching equilibrium at 10 min; 2) thiamine concentrations < 2.5 mumol/L were taken up predominantly by a saturable mechanism displaying Michaelis-Menten kinetics (K(m) 4.4 mumol/L and Jmax 2.3 pmol.mg wet tissue-1.6 min-1), whereas higher concentrations were taken up by passive diffusion; 3) thiamine transport had different capacities along the gastrointestinal tract (duodenum >> colon > stomach); and 4) thiamine uptake was competitively inhibited in the duodenum by thiamine analogs, albeit with a different order of potency compared with rats, and was blocked by 2,4-dinitrophenol. In the thiamine-deficient patient, the duodenal saturable uptake was increased, with higher K(m) and Jmax values. In conclusion, physiologic concentrations of thiamine were transported in human small intestine by a specific mechanism dependent on cellular metabolism, whose transporters appear to be down-regulated.
通过常规内窥镜检查从108名人类受试者（包括1名硫胺素缺乏患者）获取的黏膜活检标本，在含有氚标记硫胺素和[14C]葡聚糖（作为黏附黏膜水的标志物）的无氧 Krebs-Ringer 溶液（pH 7.5）中于37℃孵育。通过放射性测量法测定摄取的标记硫胺素的量。在无硫胺素缺乏临床证据的受试者中，1）十二指肠黏膜对硫胺素的摄取呈双曲线时间进程，在10分钟时达到平衡；2）硫胺素浓度<2.5 μmol/L时主要通过呈现米氏动力学的可饱和机制摄取（K(m) 4.4 μmol/L，Jmax 2.3 pmol·mg湿组织-1·6分钟-1），而较高浓度则通过被动扩散摄取；3）硫胺素在胃肠道各段的转运能力不同（十二指肠>>结肠>胃）；4）硫胺素类似物在十二指肠中竞争性抑制硫胺素摄取，尽管与大鼠相比其效力顺序不同，且被2,4-二硝基苯酚阻断。在硫胺素缺乏患者中，十二指肠的可饱和摄取增加，K(m)和Jmax值更高。总之，硫胺素的生理浓度在人类小肠中通过一种依赖细胞代谢的特定机制转运，其转运体似乎下调。
