The small intestinal epithelia of beef steers differentially express sugar transporter messenger ribonucleic acid in response to abomasal versus ruminal infusion of starch hydrolysate
2010
Liao, S.F. | Harmon, D.L. | Vanzant, E.S. | McLeod, K.R. | Boling, J.A. | Matthews, J.C.
In mammals, the absorption of monosaccharides from small intestinal lumen involves at least 3 sugar transporters (SugT): sodium-dependent glucose transporter 1 (SGLT1; gene SLC5A1) transports glucose and galactose, whereas glucose transporter (GLUT) 5 (GLUT5; gene SLC2A5) transports fructose, across the apical membrane of enterocytes. In contrast, GLUT2 (gene SLC2A2) transports all of these sugars across basolateral and apical membranes. To compare the distribution patterns and sensitivity with nutritional regulation of these 3 SugT mRNA in beef cattle small intestinal tissue, 18 ruminally and abomasally catheterized Angus steers (BW [almost equal to] 260 kg) were assigned to water (control), ruminal cornstarch (partially hydrolyzed by α-amylase; SH), or abomasal SH infusion treatments (n = 6) and fed an alfalfa-cube-based diet at 1.3 x NEm requirement. The SH infusions amounted to 20% of ME intake. After 14- or 16-d of infusion, steers were killed; duodenal, jejunal, and ileal epithelia harvested; and total RNA extracted. The relative amount of SugT mRNA in epithelia was determined using real-time reverse transcription-PCR quantification methods. Basal expression of GLUT2 and SGLT1 mRNA was greater (P < 0.09) by jejunal than by duodenal or ileal epithelia, whereas basal content of GLUT5 mRNA was greater (P [less-than or equal to] 0.02) by jejunal and duodenal than by ileal epithelia. The content of GLUT5 mRNA in small intestinal epithelia was not affected (P ≥ 0.16) by either SH infusion treatment. In contrast, GLUT2 and SGLT1 mRNA content in the ileal epithelium was increased (P [less-than or equal to] 0.05) by 6.5- and 1.3-fold, respectively, after abomasal SH infusion. Duodenal SGLT1 mRNA content also was increased (P = 0.07) by 64% after ruminal SH infusion. These results demonstrate that the ileum of beef cattle small intestine adapts to an increased luminal supply of glucose by increasing SGLT1 and GLUT2 mRNA content, whereas increased ruminal SH supply results in duodenal upregulation of SGLT1 mRNA content. These adaptive responses of GLUT2 and SGLT1 mRNA to abomasal or ruminal SH infusion suggest that beef cattle can adapt to increase their carbohydrate assimilation through small intestinal epithelia, assuming that altered SugT mRNA contents reflect the altered transport functional capacities.
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