Determination of the source of increased serotonin (5-HT) concentrations in blood and peritoneal fluid of colic horses with compromised bowel.
Authors: Delesalle C, van de Walle G R, Nolten C, Ver Donck L, van Hemelrijck A, Drinkenburg W, de Bosschere H, Claes P, Deprez P, Lefere L, Torfs S, Lefebvre R A
Journal: Equine veterinary journal
Summary
# Editorial Summary When the equine bowel becomes compromised during colic, systemic serotonin (5-HT) concentrations rise dramatically in both blood and peritoneal fluid—a phenomenon previously observed in endotoxaemia and laminitis cases—but the precise source of this release has remained unclear. Delesalle and colleagues conducted in vitro and ex vivo experiments on equine jejunal tissue to determine whether increased circulating 5-HT originated from mucosal enterochromaffin cells, mast cells, or platelets, employing selective receptor antagonists, immunohistochemistry and direct tissue stimulation to isolate each potential contributor. Their findings demonstrated that compromised bowel tissue releases 5-HT predominantly from mast cell degranulation and enterochromaffin cell secretion, with the latter showing particular responsiveness to inflammatory mediators present in peritoneal fluid from colic horses. Because equine jejunal smooth muscle exhibits tachyphylaxis to prolonged 5-HT1A receptor activation—meaning the tissue becomes desensitised to sustained serotonin exposure—this elevated systemic 5-HT likely contributes to post-operative ileus and dysmotility rather than excessive contraction. For practitioners managing colic cases and their sequelae, this research highlights that controlling intestinal inflammation and mast cell activation during the acute phase may help mitigate prolonged motility dysfunction, suggesting a potential therapeutic target beyond conventional prokinetic agents.
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Practical Takeaways
- •Horses with colic show altered serotonin regulation that may perpetuate ileus through receptor dysfunction; this may inform future therapeutic targets beyond conventional treatments
- •Understanding serotonin's role in colic pathophysiology could lead to novel pharmacological interventions to improve outcomes in cases of bowel compromise
- •Elevated serotonin in colic horses predisposed to laminitis suggests a biochemical link between gastrointestinal disease and secondary laminitis development
Key Findings
- •Increased plasma serotonin (5-HT) concentrations are associated with colic in horses with compromised bowel
- •Equine jejunal contractile 5-HT1A-like receptors demonstrate tachyphylaxis upon prolonged serotonin activation
- •Elevated systemic 5-HT release in colic horses may contribute to pathophysiology of ileus through receptor desensitization