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

The study investigates and provides evidence for the presence of cells that respond to or produce dopamine within the gastrointestinal mucosa and pancreas of horses. This research aims to shed light on the potential influence of dopamine in modulating insulin release, given its association in other species.

Research Methodology

• The researchers collected tissue samples from the stomach, small and large intestines, and pancreas of six mature horses after euthanasia.
• Immunohistochemistry was used to identify tyrosine hydroxylase (TH), the rate-limiting enzyme for dopamine production, and dopamine D2 receptors in the tissue sections.
• The researchers also performed additional immunostaining to identify alpha cells, beta cells, and enteroendocrine cells.
• The concentration of dopamine in stomach contents and faeces was identified using high-performance liquid chromatography with electrochemical detection.

Research Findings

• The study found that gastric parietal cells expressed both TH and D2 receptors, suggesting they have the capability to produce and respond to dopamine.
• Similar concentrations of dopamine were found in the stomach contents and faeces.
• Dopamine D2 receptors were present in duodenal epithelial cells, and a subset of enteroendocrine cells across the gastrointestinal tract were found to be positive for the D2 receptor.
• In pancreatic islets, TH was present in alpha cells, whereas D2 receptors were strongly expressed in beta cells and variably expressed in alpha cells.

Research Implications

• The study’s findings are in line with previous studies from other species and suggest a potential role of dopamine as a paracrine messenger in the gastrointestinal mucosa and endocrine pancreas of horses.
• The evidence of dopamine influence on insulin release from the pancreas in horses may provide important insights into the treatment of insulin dysregulation in these animals.
• Though the research provides preliminary evidence, further dynamic studies are required to better understand the role of dopamine in the secretion of insulin and glucagon in horses.