Studies in vitro of equine intestinal glucagon-like peptide-2 secretion

Equine insulin dysregulation (ID) is a significant metabolic problem because the hyperinsulinaemia that develops increases the animal's risk of developing laminitis, a debilitating foot condition. The role of gastrointestinal factors, such as incretin hormones, in the pathogenesis of ID and hyperinsulinaemia in horses is poorly understood, particularly in comparison to other species. Glucagon-like peptide-2 (GLP-2) is an intestinotrophic peptide released from L cells in the gastrointestinal tract and is implicated in metabolic dysfunction in other species. The aim of this study in vitro was to establish basic physiological understanding about intestinal secretion of GLP-2 in horses. Basal and glucose-stimulated GLP-2 secretion was measured in post-mortem tissue samples from the duodenum, jejunum, and ileum. We observed that GLP-2 secretion was minimal in samples from the duodenum compared to the jejunum and ileum (5-9-fold higher; P < 0.05). Furthermore, GLP-2 secretion was not responsive to glucose stimulation in the ileum or duodenum but was responsive to glucose in the jejunum. This effect in the jejunum was inhibited by 30 % (P = 0.02) using phlorizin, a selective sodium-glucose cotransporter-1 (SGLT-1) inhibitor, and by 38 % (P = 0.04) using phloretin, a non-selective SGLT-1/GLUT-2 inhibitor. The localisation of glucose-responsive GLP-2 secretion in the jejunum might be relevant to the development of post-prandial hyperinsulinaemia. This study has provided data on GLP-2 secretion from the equine small intestine that will enable more complex and dynamic studies on the pathogenesis of ID.