Molecular characterisation of fructose transport in equine small intestine.

REASONS FOR PERFORMING STUDY: 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.

OBJECTIVES

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.

POTENTIAL RELEVANCE: The molecular probes produced in these studies can be used as diagnostic aids to determine equine intestinal monosaccharide malabsorption.