Evidence for dopamine production and distribution of dopamine D2 receptors in the equine gastrointestinal mucosa and pancreas.
Authors: Galinelli Nicolas C, Bamford Nicholas J, de Laat Melody A, Sillence Martin N, Harris Patricia A, Bailey Simon R
Journal: PloS one
Summary
Insulin dysregulation and its associated laminitis risk in horses may be modulated by dopamine signalling, a mechanism well-documented in other species but unexplored in equines; this study sought to establish whether horses possess the anatomical substrate—dopamine-producing and dopamine-responsive cells—necessary for such regulation. Immunohistochemical analysis of gastrointestinal and pancreatic tissues from six horses revealed that gastric parietal cells express both tyrosine hydroxylase (the rate-limiting dopamine synthesis enzyme) and D2 dopamine receptors, duodenal epithelial cells and scattered enteroendocrine cells express D2 receptors, and critically, pancreatic alpha cells produce dopamine whilst beta cells strongly express D2 receptors, suggesting a local paracrine feedback mechanism. Dopamine was detected at consistent concentrations in both stomach contents and faeces, indicating availability within the gastrointestinal environment. These findings provide the anatomical framework supporting dopamine's potential role in suppressing insulin secretion in horses, mirroring mechanisms in humans and rodents, though functional studies remain necessary to confirm whether manipulation of dopamine signalling could offer therapeutic benefit for insulin dysregulation and laminitis prevention. For practitioners managing metabolic disease, this work opens possibilities for future investigations into whether dietary or pharmaceutical interventions targeting dopamine pathways might help regulate hyperinsulinaemia in susceptible horses.
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Practical Takeaways
- •This foundational work suggests dopamine may modulate insulin secretion in horses similarly to other species; future research may reveal dietary or management strategies to manipulate this pathway for laminitis prevention
- •The presence of dopamine in stomach contents implies the gastrointestinal tract is an active site of dopamine production—nutritional or probiotic interventions targeting this system warrant investigation
- •Current findings are descriptive only; do not change clinical practice until dynamic studies clarify dopamine's functional role in equine insulin regulation
Key Findings
- •Gastric parietal cells express both tyrosine hydroxylase and dopamine D2 receptors, indicating capacity for dopamine production and response
- •Dopamine D2 receptors are expressed in duodenal epithelial cells and variably in enteroendocrine cells throughout the gastrointestinal tract
- •Pancreatic α cells produce dopamine via tyrosine hydroxylase while β cells strongly express D2 receptors, suggesting a paracrine regulatory pathway
- •Dopamine is present in equine stomach contents and faeces at similar concentrations, indicating gastrointestinal production and distribution