Plasma 5-hydroxytryptamine constricts equine digital blood vessels in vitro: implications for pathogenesis of acute laminitis.
Authors: Bailey, Elliott
Journal: Equine veterinary journal
Summary
# Editorial Summary: 5-HT and Digital Vasoconstriction in Laminitis Bailey and Elliott's 1998 investigation examined why serotonin (5-hydroxytryptamine; 5-HT) might selectively compromise blood flow to the equine digit during acute laminitis by testing isolated blood vessel rings from different anatomical regions. Using in vitro tissue baths and high-performance liquid chromatography, they demonstrated that digital arteries are extraordinarily sensitive to 5-HT—approximately 18 and 41 times more reactive than facial and tail arteries respectively—and that normal circulating plasma levels (6.7 × 10⁻⁸ mol/l free 5-HT) are sufficient to cause meaningful constriction of digital vessels whilst leaving systemic circulation largely unaffected. Notably, removal of the endothelium did not diminish digital artery responsiveness to 5-HT, suggesting a direct myogenic mechanism rather than endothelium-dependent regulation, and their digital artery bioassay correlated excellently with direct chemical measurement (r² = 97.2%). For practitioners managing acute laminitis, these findings provide mechanistic support for the role of platelet activation and 5-HT release in precipitating the severe digital ischaemia characteristic of the condition, potentially justifying investigation into serotonin antagonists as adjunctive therapy and highlighting why early antiplatelet or anticoagulant protocols may be particularly valuable in laminitis cases.
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Practical Takeaways
- •Elevated plasma 5-HT (particularly from platelet release) may contribute to pathological digital vasoconstriction during laminitis episodes through selective sensitivity of digital arteries
- •5-HT receptor antagonists could represent a potential therapeutic target to prevent or reduce digital vascular compromise in acute laminitis
- •Digital blood vessels appear uniquely sensitive to circulating 5-HT compared to other peripheral vessels, making them vulnerable during systemic platelet activation or endotoxemia
Key Findings
- •5-HT is 17.7 times more potent as a vasoconstrictor in equine digital arteries compared to facial arteries
- •Platelet-rich equine plasma contains 5-HT at concentration 1.77±0.36 × 10⁻⁶ mol/l, approximately 26-fold higher than platelet-poor plasma
- •Plasma-induced digital artery constriction was almost completely inhibited by 5-HT receptor antagonists ketanserin and methiothepin
- •Normal circulating free 5-HT concentrations may be sufficient to partially constrict digital blood vessels in vivo but insufficient to affect other peripheral vessels