Expression of sweet receptor components in equine small intestine: relevance to intestinal glucose transport.
Abstract: The heteromeric sweet taste receptor T1R2-T1R3 is expressed on the luminal membrane of certain populations of enteroendocrine cells. Sensing of sugars and other sweet compounds by this receptor activates a pathway in enteroendocrine cells, resulting in secretion of a number of gut hormones, including glucagon-like peptide 2 (GLP-2). This subsequently leads to upregulation in the expression of intestinal Na(+)/glucose cotransporter, SGLT1, and increased intestinal glucose absorption. On the basis of the current information available on the horse genome sequence, it has been proposed that the gene for T1R2 (Tas1R2) is absent in the horse. We show here, however, that horses express both the mRNA and protein for T1R2. Equine T1R2 is most closely homologous to that in the pig and the cow. T1R2 protein, along with T1R3, α-gustducin, and GLP-2 proteins are coexpressed in equine intestinal endocrine cells. Intravenous administration of GLP-2, in rats and pigs, leads to an increase in the expression of SGLT1 in absorptive enterocytes and enhancement in blood glucose concentrations. GLP-2 receptor is expressed in enteric neurons, excluding the direct effect of GLP-2 on enterocytes. However, electric stimulation of enteric neurons generates a neural response leading to SGLT1 upregulation, suggesting that sugar in the intestine activates a reflex increase in the functional expression of SGLT1. Horses possess the ability to upregulate SGLT1 expression in response to increased dietary carbohydrates, and to enhance the capacity of the gut to absorb glucose. The gut sweet receptor provides an accessible target for manipulating the equine gut to absorb glucose (and water), allowing greater energy uptake and hydration for hard-working horses.
Publication Date: 2012-05-02 PubMed ID: 22552794DOI: 10.1152/ajpregu.00031.2012Google Scholar: Lookup
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- Comparative Study
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research explores the presence and role of sweet taste receptor T1R2-T1R3 in horses’ small intestine that enables an upsurge in glucose (and water) absorption, providing potential dietary strategy for energy intake and hydration in high-performing horses.
Understanding Sweet Receptor in Equine Small Intestine
- The study primarily revolves around a heteromeric sweet taste receptor, T1R2-T1R3, which resides on the luminal membrane of specific enteroendocrine cells. This receptor senses sugars and other sweet compounds and triggers a certain pathway in the enteroendocrine cells.
- Activation of this pathway results in the secretion of various gut hormones, including glucagon-like peptide 2 (GLP-2). The secretion of GLP-2 eventually leads to an upsurge in the expression of the intestinal Na(+)/glucose cotransporter, SGLT1, which facilitates an increase in intestinal glucose absorption.
Relevance to Horses’ Glucose Transport
- Contrary to the previous presumptions based on the horse genome sequence suggesting the absence of the T1R2 (Tas1R2) gene in horses, this research shows that horses express both the mRNA and protein for T1R2.
- This equine T1R2 is found to be most homologous to that in pigs and cows. Further, T1R2 protein, along with T1R3, α-gustducin, and GLP-2 proteins, are co-expressed in equine intestinal endocrine cells.
Activation and Impact of GLP-2 Receptor
- In rats and pigs, intravenous administration of GLP-2 leads to an escalation in the expression of SGLT1 in absorptive enterocytes and enhancement in blood glucose concentrations.
- The GLP-2 receptor is said to be expressed in enteric neurons, which excludes the direct effect of GLP-2 on enterocytes. Yet, electric stimulation of enteric neurons generates a neural response leading to SGLT1 upregulation. This implies that sugar in the intestine activates a reflex increase in the functional expression of SGLT1.
Implications and Applications
- The study showed horses possess the ability to upregulate SGLT1 expression proportionate to increased dietary carbohydrates. This suggests the horses’ gut’s capacity to absorb glucose improves with high carbohydrate intake, providing them with additional energy and hydration.
- The presence and understanding of the gut sweet receptor opens up an accessible target for manipulating the equine gut to absorb glucose (and water), which is beneficial for hard-working horses for increasing energy uptake and hydration.
Cite This Article
APA
Daly K, Al-Rammahi M, Arora DK, Moran AW, Proudman CJ, Ninomiya Y, Shirazi-Beechey SP.
(2012).
Expression of sweet receptor components in equine small intestine: relevance to intestinal glucose transport.
Am J Physiol Regul Integr Comp Physiol, 303(2), R199-R208.
https://doi.org/10.1152/ajpregu.00031.2012 Publication
Researcher Affiliations
- Epithelial Function and Development Group, Department of Functional and Comparative Genomics, Institute of Integrative Biology, Faculty of Health and Life Sciences, University of Liverpool, Liverpool, UK.
MeSH Terms
- Amino Acid Sequence
- Animals
- Biological Transport / drug effects
- Biological Transport / physiology
- Cats
- Dietary Carbohydrates / pharmacokinetics
- Energy Metabolism / drug effects
- Energy Metabolism / physiology
- Enteroendocrine Cells / cytology
- Enteroendocrine Cells / metabolism
- Epithelial Cells / cytology
- Epithelial Cells / metabolism
- Female
- Glucagon-Like Peptide 2 / metabolism
- Glucose / metabolism
- Horses / metabolism
- Intestine, Small / cytology
- Intestine, Small / metabolism
- Male
- Molecular Sequence Data
- Receptors, G-Protein-Coupled / analysis
- Receptors, G-Protein-Coupled / metabolism
- Sodium-Glucose Transporter 1 / metabolism
- Swine
- Tongue / cytology
- Tongue / metabolism
- Transducin / metabolism
Citations
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