A PHYSIOLOGICAL LEVEL OF RHUBARB FIBER INCREASES PROGLUCAGON GENE-EXPRESSION AND MODULATES INTESTINAL GLUCOSE-UPTAKE IN RATS

Previous work demonstrated that a high fiber diet upregulates progluca gon mRNA and secretion of glucagon-like peptide-1 [GLP-1(7-37)] and in sulin compared with an elemental fiber-free diet. This study examined whether similar intakes of fibers differing in physiochemical and ferm entative properties alter the expression of intestinal hormones and in testinal absorptive properties. Sprague-Dawley rats were fed either a 50 g/kg cellulose or rhubarb fiber diet for 14 d. Ileal proglucagon mR NA levels were significantly higher in rats fed rhubarb fiber than in those fed cellulose fiber (9.3 +/- 0.9 vs. 6.2 +/- 1.0 densitometer un its). Proglucagon mRNA in the colon did not differ between diet treatm ents. Plasma c-peptide concentrations were significantly higher 30 min after an oral glucose tolerance test in the rhubarb vs. cellulose gro up (1627 +/- 67 vs. 1290 +/- 71 pmol/L). Passive permeability, measure d by the uptake of L-glucose, was significantly higher in the jejunum of rats fed cellulose compared with those fed rhubarb fiber. Adjusting total glucose uptake for passive permeability and unstirred water lay er resistance resulted in a higher K-m being calculated for the jejunu m and ileum of the cellulose fiber group. Jejunal and ileal carrier-me diated uptakes (V-max) were not altered by diet and reflected the lack of difference between groups in sodium-dependent glucose cotransporte r (SGLT-1) and sodium-independent glucose transporter (GLUT2) mRNA lev els. Replacing cellulose fiber with rhubarb fiber in a diet upregulate d ileal proglucagon mRNA and resulted in a reduced passive permeabilit y but did not affect glucose transport of the small intestine. This wo rk establishes the importance of dietary fiber fermentability in modul ating intestinal proglucagon expression and possibly glucose homeostas is.