title: Age-associated changes in intestinal fructose uptake are not explained by alterations in the abundance of GLUT5 or GLUT2.
abstract: A reduction in nutrient absorption may contribute to malnourishment in the elderly. The objectives of this study were to determine the effects of aging on the absorption of fructose in rats, as well as the mechanisms of these adaptive changes. Male Fischer 344 rats aged 1, 9, and 24 months were fed standard Purina chow for 2 weeks (PMI #5001, PMI Nutritionals, Brentwood, MO). The uptake of (14)C-labeled D-fructose was determined in vitro using the intestinal sheet method. Intestinal samples were taken for RNA isolation and for brush border membrane (BBM) and basolateral membrane (BLM) preparation. Northern blotting, Western blotting, and immunohistochemistry were used to determine the effects of age and diet on GLUT5 and GLUT2. When expressed on the basis of intestinal or mucosal weights, aging was associated with a decline in jejunal and ileal fructose uptake, whereas jejunal fructose uptake was increased when expressed on the basis of serosal or mucosal surface area. The alterations in fructose uptake were not paralleled by changes in GLUT5 or GLUT2 abundance. These results indicate that 1) the effect of age on fructose uptake depends on the method used to express results, and 2) the age-associated changes in uptake are not explained by alterations in GLUT5 and GLUT2.
authors.affiliation: Nutrition and Metabolism Group, Division of Gastroenterology, Department of Medicine, 5146 Dentistry Pharmacy Building, University of Alberta, Edmonton, AB T6G 2N8, Canada.
authors.forename: Laurie A
authors.initials: LA
authors.lastname: Drozdowski
authors.forename: Trudy D
authors.initials: TD
authors.lastname: Woudstra
authors.forename: Gary E
authors.initials: GE
authors.lastname: Wild
authors.forename: M Tom
authors.initials: MT
authors.lastname: Clandinin
authors.forename: Alan B R
authors.initials: AB
authors.lastname: Thomson
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002250:Carbon Radioisotopes; D004032:Diet; D005632:Fructose / Q000493:pharmacokinetics*; D051273:Glucose Transporter Type 2; D051296:Glucose Transporter Type 5; D007082:Ileum / Q000737:chemistry / Q000378:metabolism; D007150:Immunohistochemistry; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000033:anatomy & histology / Q000378:metabolism; D007583:Jejunum / Q000737:chemistry / Q000378:metabolism; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000032:analysis* / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D002250:Carbon Radioisotopes; D051273:Glucose Transporter Type 2; D051296:Glucose Transporter Type 5; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D005632:Fructose