Molecular characterisation of fructose transport in equine small intestine.
BACKGROUND
Fructose can be a suitable carbohydrate supplement for horses before and/or during endurance exercise. In comparison to glucose, the ingestion of fructose results in a lower insulin peak and less marked fluctuations in blood glucose during exercise, potentially avoiding hypoglycaemia-induced exhaustion.


OBJECTIVE
To assess the capacity of the equine small intestine to absorb fructose and to determine the mechanism, molecular structure and properties of equine intestinal fructose transport.


METHODS
Using PCR-based strategies, RNA isolated from equine small intestine and primers designed to homologous regions of the fructose transporter, GLUT5, cDNA of other species, we cloned and sequenced equine GLUT5 (eGLUT5). Northern and western blot analyses, in conjunction with immunohistochemistry, utilising eGLUT5 cDNA and antibodies, assessed expression of eGLUT5 along the longitudinal and radial axes of the small intestine. Functional properties of fructose transport in intestinal brush-border membrane vesicles were measured using the rapid-filtration technique.


RESULTS
eGLUT5 is expressed in the villus enterocytes with highest levels in duodenum>jejunum and lowest in the ileum. Kinetic studies indicate eGLUT5 is a low affinity, high capacity transporter.


CONCLUSIONS
Equine small intestine has the capacity to absorb fructose.


CONCLUSIONS
The molecular probes produced in these studies can be used as diagnostic aids to determine equine intestinal monosaccharide malabsorption.
Epithelial Function and Development Group, Department of Veterinary Preclinical Sciences, The University of Liverpool, Liverpool L69 7ZJ, UK.
E Fernandez-Castaño
EF
Merediz
J
J
Dyer
K S H
KS
Salmon
S P
SP
Shirazi-Beechey
D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000378:metabolism / Q000493:pharmacokinetics*; D005632:Fructose / Q000378:metabolism / Q000493:pharmacokinetics*; D005767:Gastrointestinal Diseases / Q000175:diagnosis / Q000662:veterinary; D051296:Glucose Transporter Type 5; D006734:Horse Diseases / Q000175:diagnosis; D006736:Horses / Q000502:physiology*; D007150:Immunohistochemistry / Q000662:veterinary; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000201:enzymology / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism*; D008871:Microvilli / Q000201:enzymology / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000235:genetics*; D010807:Physical Endurance / Q000187:drug effects; D016133:Polymerase Chain Reaction / Q000379:methods / Q000662:veterinary; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D051296:Glucose Transporter Type 5; D009004:Monosaccharide Transport Proteins; D005632:Fructose