Evidence for dopamine production and distribution of dopamine D2 receptors in the equine gastrointestinal mucosa and pancreas.

Insulin dysregulation in horses is characterised by hyperinsulinaemia and/or tissue insulin resistance and is associated with increased risk of laminitis. There is growing evidence in other species that dopamine attenuates insulin release from the pancreas; however, this has yet to be examined in horses. The present study aimed to identify whether there are cells capable of producing or responding to dopamine within the equine gastrointestinal mucosa and pancreas. Tissue samples were collected from the stomach, small and large intestines, and pancreas of six mature horses following euthanasia. Samples of stomach contents and faeces were also collected. Immunohistochemistry was performed to identify tyrosine hydroxylase (TH), the rate-limiting enzyme for dopamine production, and dopamine D2 receptors in tissue sections. Additional immunostaining for glucagon, insulin and chromogranin A was performed to identify α cells, ß cells and enteroendocrine cells, respectively. Gastric parietal cells expressed both TH and D2 receptors, indicating that they are capable of both producing and responding to dopamine. Dopamine was quantified in stomach contents and faeces by high-performance liquid chromatography with electrochemical detection, with similar concentrations found at both sites. Dopamine D2 receptors were expressed in duodenal epithelial cells but not more distally. A subset of enteroendocrine cells, located sporadically along the gastrointestinal tract, were found to be immunopositive for the D2 receptor. In pancreatic islets, TH was present in α cells, while D2 receptors were strongly expressed in ß cells and variably expressed in α cells. These findings are consistent with studies of other species; however, dynamic studies are required to further elucidate the role of dopamine in the modulation of insulin and glucagon secretion in horses. This descriptive study provides preliminary evidence for a potential role of dopamine to act as a paracrine messenger in the gastrointestinal mucosa and endocrine pancreas of horses.

High intake of sugars and starch, low number of meals and low roughage intake are associated with Equine Gastric Ulcer Syndrome in a Belgian cohort.

Equine gastric ulcer syndrome (EGUS) is a pathological condition affecting the glandular and squamous regions of the stomach. It is characterized by non-specific clinical signs, behavioural changes or can also be found without any overt clinical manifestations. Nutritional factors such as intermittent feeding, high sugars and starch intake, large amounts of straw as forage and prolonged time without access to forage have all been associated with an increased risk of equine squamous gastric disease (ESGD). The aim of this study was to investigate which nutritional practices are commonly seen in clinical ESGD cases in Belgium. Medical records of 27 horses referred to the equine nutritional service at Ghent University (2013-2018) due to equine gastric ulcer lesions were reviewed. Twenty-one healthy horses referred for dietary evaluation during the same period were selected as control cases (CC). Dietary evaluation was performed on an individual basis. Forage/concentrate ratio on dry matter basis, forage content in the diet, total dietary sugars and starch intake per day and per meal were analysed. Retrospective descriptive and statistical analyses were performed. Significantly, higher amounts of forage intake (%DM per BW) in the CC vs. ESGD group were noted (p ≤ .05) with average values of 1.39 (SD ± 0.27) and 1.27 (SD ± 0.70) respectively. There were no significant differences for sugars and starch intake in g/kg BW/day (p = .18). However, the sugars and starch intake per meal (g/kg BW/meal) in the CC group (average value 1.06, SD ± 0.56) was significantly (p < .001) lower than in the EGUS group (average value 1.85 SD ± 0.78). Forage intake below the recommended absolute minimum value as well as high sugars and starch intake were most commonly associated with EGUS in the present case series. An adequate diet formulation taking into account these main nutritional factors is therefore essential to avoid gastric problems in horses.