The effect of rapid changes in plasma sugar concentration on the brush-border potential difference in rat jejunum

Intestinal glucose absorption in calves as affected by different carbohydrate sources

From numerous recent studies, it has been demonstrated that the development of the forestomach system in ruminants and thus microbial carbohydrate fermentation do not exclude the potential of the small intestines for enzymatic carbohydrate digestion and subsequent monosaccharide absorption. However, the role of regulatory nutritional factors is still under discussion. Therefore, we investigated the kinetic parameters of intestinal Na(+) -dependent glucose absorption and SGLT1 expression using isolated brush border membrane vesicles (BBMV) from the jejunum of 10-week-old calves kept on either hay, concentrate or corn silage-based diets in addition to milk replacer. While the maximal transport capacity was significantly higher for concentrate and corn silage-fed animals, SGLT1 protein expression was highest in BBMV isolated from hay-fed animals. This observation differs from the prevalent conception that induction of Na(+) -dependent glucose uptake via SGLT1 is based on an increased number of transporters at the brush border membrane.

Apical sodium–glucose co-transport can be regulated by blood-borne glucose in the ruminal epithelium of sheep (Ovis aries, Merino breed)

The intestinal Na-dependent D-glucose co-transporter (SGLT)-1 in sheep is under dietary regulation by luminal substrates. The aim of the present study was to find out whether the SGLT-1 in the forestomach of sheep is also regulated by sugars. Furthermore, the location of a possible glucosensor (luminalv.intracellularv.basolateral) was to be elucidated. Ruminal epithelia of sheep (Ovis aries, Merino breed) were pre-incubated in Ussing chambers with various substrates on the mucosal (i.e. luminal) or serosal (i.e. blood) side. This pre-incubation period was followed by a second pre-incubation period without the tested substrates (washout period). Thereafter, apical D-glucose uptake by ruminal epithelial cells was determined with 200 μmol D-[14C]glucose/l in the absence or co-presence of the SGLT-1 inhibitor, phlorizin. Pre-incubation with D-glucose on the mucosal side had no significant effect on apical D-glucose uptake (P>0.05). In contrast, pre-incubation with D-glucose, D-mannose, 3-O-methyl-D-glucose or sucrose on the serosal side significantly increased D-glucose uptake compared with mannitol-treated controls (P<0.05). Serosal pre-incubation with cellobiose or D-xylose had no effect. The stimulation of D-glucose uptake by serosal D-glucose pre-incubation was concentration dependent, with maximal stimulation at about 10 mmol/l. We conclude that the ruminal SGLT-1 can be up-regulated in a concentration-dependent manner by blood-borne D-glucose via an extracellular sugar-sensing mechanism.