FRUCTOSE TRANSPORT MECHANISMS IN HUMANS

Background & Aims: The possible mechanisms of fructose transport ave d iffusion, a disaccharidase-related transport system, and glucose-facil itated fructose transport. However, these mechanisms in the human smal l intestine have not been systematically examined. This study was desi gned to investigate the mechanisms of fructose transport in the human duodenojejunum. Methods: A triple-lumen tube was fluoroscopically posi tioned in the duodenojejunum of 7 men, Nine carbohydrate-electrolyte s olutions were perfused at the rate of 15 mL/min. Acarbose and lactulos e were used to examine the disaccharidase-related transport system and glucose-facilitated fructose transport, respectively. Results: Fructo se absorption was greater (P < 0.05) from fructose-glucose (FruGlu) an d fructose-glucose-acarbose (FruGluA) solutions than from fructose-man nitol (FruMann) and fructose-mannitol-acarbose (FruMannA) solutions, b ut there was no difference between FruGlu and FruGluA solutions. A suc rose solution produced greater (P < 0.05) sucrose absorption than a su crose-acarbose solution. Lactulose absorption (0.016-0.039 mmol.h(-1). cm(-1)) was observed from solutions containing glucose or sucrose. Wat er absorption was not different among sucrose, FruGlu, and glucose sol utions. FruMann solution produced net water secretion, These data sugg est that free fructose and glucose transport were not inhibited by aca rbose and that the presence of glucose induced lactulose absorption an d enhanced fructose absorption. Conclusions: Fructose is transported t ranscellularly by facilitated diffusion and paracellularly (based on l actulose transport) via glucose-activated solution drag. In the human small intestine, free fructose and glucose transport does not occur vi a the disaccharidase system.