Active transport of 3-O-methyl-glucose by the small intestine in chronically catheterized rats.

2007

Section: Effective Pore Size In Tight Junctions Does Not Seem Greater Insupporting

confidence: 67%

Mechanistic bases for differences in passive absorption

Lavin

McWhorter

2007

“…In laboratory rats, the absorption rate of the nonmetabolizable, actively transported 3-O-methyl-D-glucose apparently exceeded that of L-glucose by about 9:1, implying that most glucose was absorbed actively (Uhing and Kimura, 1995). Similar conclusions have been drawn for dogs (Lane et al, 1999) and humans (Fine et al, 1993).…”

supporting

confidence: 61%

How the house sparrowPasser domesticusabsorbs glucose

Chang

2004

SUMMARY According to the hypothesis that most glucose absorption occurs passively across intestinal tight junctions (paracellular absorption), one would predict fairly similar rates of in vivo absorption of l-glucose,the stereoisomer of d-glucose that is absorbed only passively and is not catabolized, and of 3-O-methyl-d-glucose(3OMd-glucose), the d-glucose analogue that is actively and passively transported and not catabolized. In house sparrows Passer domesticus, we applied a pharmacokinetic method to measure simultaneous in vivo absorption of [14C]l-glucose and[3H]3OMd-glucose in a situation in which intestinal glucose transporters were relatively saturated (gavage solution contained 200 mmol l-1 3OMd-glucose). Fractional absorptions(F) were not significantly different between[3H]3OMd- and [14C]l-glucose (0.80 vs 0.79), and the apparent rates of absorption did not differ significantly. When we performed the same experiment on other sparrows in a situation in which intestinal glucose transporters were relatively unsaturated(200 mmol l-1 mannitol replaced 3OMd-glucose in the gavage solution), the apparent rate of absorption was significantly reduced for [14C]l-glucose by 39% and for[3H]3OMd-glucose by 26%. A simulation model showed that a reduction is not predicted if most of the[3H]3OMd-glucose is actively absorbed, because the absorption rate of the tracer should increase when competitive inhibitor(unlabeled 3OMd-glucose) is removed. The similar extent and rates of absorption of [3H]3OMd- and[14C]l-glucose, and the acceleration of their rates of absorption in the presence of luminal 3OMd-glucose, are most consistent with Pappenheimer's hypothesis that the majority of dietary d-glucose is absorbed passively.

“…This value was likely an overestimate because the paracellular probe molecules that were used were smaller in molecular size than glucose, and smaller molecules cross the TJ faster (Karasov, 2011). Thus, the results with the rats and marmosets indicate that the majority of glucose was absorbed by mediated pathway(s), as was found previously by Uhing and Kimura (1995b) in rats and by Fine et al (1993Fine et al ( , 1994Fine et al ( , 1995 in a different primate -humans. In contrast, the same ratio in the four flyers depicted in Fig.…”

Section: Controversy About the Contribution Of Glut2mentioning

confidence: 59%

Integrative physiology of transcellular and paracellular intestinal absorption

2017

Glucose absorption by the small intestine has been studied for nearly a century. Despite extensive knowledge about the identity, functioning and regulation of the relevant transporters, there has been and there remains controversy about how these transporters work in concert to determine the overall epithelial absorption of key nutrients (e.g. sugars, amino acids) over a wide range of dietary and/ or luminal concentrations. Our broader, integrative understanding of intestinal absorption requires more than the reductionist dissection of all the components and their elaboration at molecular and genetic levels. This Commentary emphasizes the integration of discrete molecular players and processes (including paracellular absorption) that, in combination, determine the overall epithelial absorption of key nutrients (e.g. sugars, amino acids) and putative anti-nutrients (watersoluble toxins), and the integration of that absorption with other downstream processes related to metabolic demands. It identifies historic key advances, controversies and future research ideas, as well as important perspectives that arise through comparative as well as biomedical physiological research.