Molecular characterisation of fructose transport in equine small intestine

Abstract

Summary 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.

The effect of harvest time of forage on carbohydrate digestion in horses quantified by in vitro and mobile bag techniques

“…The carbohydrates constitute a large proportion of the forage and are important energy sources for all horses. The structural carbohydrates are fermented by hindgut microbes to short-chained fatty acids (SCFA) providing the largest energy source for the horse ( Janis, 1976 ), and the WSC are mainly digested and absorbed as glucose and fructose in the small intestine ( Dyer et al, 2002 ; Merediz et al, 2004 ). Currently it is not clearly known how and where fructans are digested within the equine gastro-intestinal tract.…”

Nutritional tips for veterinarians

“…The basic digestive processes are similar to those of other monogastric animals with dietary nonstructural carbohydrates and proteins being hydrolysed by the pancreatic and intestinal brush border enzymes Dyer et al 2002Dyer et al , 2009Richards et al 2004;Merritt and Julliand 2013). The transport mechanisms for glucose and fructose are also believed to be similar to those in other species, although the equid small intestine has a limited capacity to transport glucose compared with an omnivorous mammal such as the pig (Merediz et al 2004;Woodward et al 2013). Less is known about protein and fat assimilation (Cehak et al 2013), although interestingly equine pancreatic tissue contains relatively high concentrations of lipase (Lorenzo-Figueras et al 2007).…”

“…The transport mechanisms for glucose and fructose are also believed to be similar to those in other species, although the equid small intestine has a limited capacity to transport glucose compared with an omnivorous mammal such as the pig (Merediz et al . ; Woodward et al . ).…”