The effects of vasoactive amines found in the equine hindgut on digital blood flow in the normal horse.
Authors: Bailey S R, Menzies-Gow N J, Marr C M, Elliott J
Journal: Equine veterinary journal
Summary
# Editorial Summary Bailey and colleagues investigated whether vasoactive amines produced by hindgut bacteria could directly trigger the digital vasoconstriction characteristic of acute laminitis, using intravenous infusions of tryptamine and phenylethylamine in standing, unsedated horses whilst measuring digital blood flow via Doppler ultrasound and monitoring hoof wall temperature. Both compounds induced substantial reductions in digital arterial blood flow (approximately 29% for tryptamine and 18% for phenylethylamine) without affecting systemic blood pressure or heart rate, alongside measurable decreases in dorsal hoof wall temperature and elevated plasma serotonin concentrations, suggesting the amines' effects were mediated partly through displacement of serotonin from platelets. These findings provide mechanistic insight into how hindgut disturbances following carbohydrate overload might selectively compromise perfusion to the digit—a plausible link between the initiating digestive events and the vascular pathology of laminitis that has previously remained unclear. For practitioners, this work implies that therapeutic strategies targeting amine production or clearance during acute colitis or grain overload episodes could potentially mitigate laminitis risk, though the authors acknowledge further investigation in naturally affected animals is needed to establish whether amines represent a clinically meaningful intervention point in the disease cascade.
Read the full abstract on PubMed
Practical Takeaways
- •Hindgut dysbiosis and bacterial amine production following carbohydrate overload may directly trigger the digital vasoconstriction seen in laminitis—managing hindgut health and preventing carbohydrate overload is critical
- •Digital blood flow reduction occurs selectively in the foot without systemic cardiovascular effects, explaining why laminitis can develop acutely without obvious signs of shock
- •Future laminitis treatments may target amine-mediated vasoconstriction or platelet 5-HT displacement as a novel therapeutic approach
Key Findings
- •Tryptamine infusion (1.6 µg/kg/min) caused 29.2% decrease in digital arterial blood flow without affecting systemic blood pressure or heart rate
- •Phenylethylamine infusion (2.13 µg/kg/min) caused 18.4% decrease in digital arterial blood flow with similar selective vasoconstrictor effects
- •Both amines decreased dorsal hoof wall temperature by 0.5-0.6°C and increased plasma 5-HT concentration
- •Hindgut-derived amine compounds may contribute to digital vasoconstriction following carbohydrate overload and represent a potential therapeutic target in laminitis