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Effects of monoamines formed in the cecum of horses on equine digital blood vessels and platelets.
Abstract: To determine in vitro vasoactive potency of monoamines formed in the cecum and found in the systemic circulation of horses. Methods: Segments of digital blood vessels obtained from 6 healthy mixed-breed horses and ponies euthanatized at an abattoir and platelets isolated from 4 healthy ponies. Methods: Paired rings of digital artery and vein from the same horse were examined, and isometric tension was recorded. Concentration-response curves for tryptamine (TRP), tyramine (TYR), phenylethylamine (PEA), isoamylamine (IAA), and isobutylamine (IBA) were obtained. Vasoconstrictor mechanisms were investigated for TRP and TYR by the use of antagonists. Washed platelets loaded with [3H]-5-hydroxytryptamine (5-HT) were incubated with monoamines; the amount of radioactivity displaced after 30 minutes was estimated. Results: TRP, TYR, and PEA were potent constrictors of arteries and veins, with TRP and TYR being more potent in veins than arteries. Constrictions induced by TYR were inhibited by benextramine (alpha-antagonist) and nisoxetine (neuronal-uptake blocker), whereas TRP responses were inhibited by ketanserin (5-HT receptor antagonist). All 5 amines displaced 5-HT from platelets with the order of potency being TYR > TRP > PEA > IAA > IBA. Conclusions: Amines from the equine cecum cause digital vasoconstriction. The most potent (TRP and TYR) cause selective venoconstriction. Tyrosine activates predominantly alpha-adrenoceptors through the release of neuronal norepinephrine, whereas TRP activates 5-HT receptors. All amines tested released 5-HT from platelets. Amines formed in the cecum and released into the systemic circulation warrant additional investigation as trigger factors for digital ischemia and subsequent laminitis.
Publication Date: 2003-09-19 PubMed ID: 13677390DOI: 10.2460/ajvr.2003.64.1124Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research explored the impact of various monoamines, substances created in the cecum of the horse’s intestine, on the animal’s digital blood vessels and platelets. The study found that these monoamines have the ability to constrict arteries and veins with varying degrees of potency, and suggest further scrutiny as potential triggers for specific horse health complications.
Methodology
- The subjects of this study were healthy mixed-breed horses and ponies. Digital blood vessels from six horses and platelets from four ponies were obtained.
- Different segments of blood vessels (arteries and veins) were examined and isometric tension was recorded.
- Concentration-response curves were created for the different monoamines – tryptamine (TRP), tyramine (TYR), phenylethylamine (PEA), isoamylamine (IAA), and isobutylamine (IBA).
- The vasoconstrictor mechanisms of TRP and TYR were further investigated using antagonists.
- Platelets combined with [3H]-5-hydroxytryptamine (5-HT) were exposed to the monoamines to determine the amount of radioactivity displaced after 30 minutes.
Findings
- TRP, TYR, and PEA were found to be potent constrictors of arteries and veins, with TRP and TYR exerting a greater effect on veins than arteries.
- The constrictions prompted by TYR were found to be inhibited by benextramine (an alpha-antagonist) and nisoxetine (neuronal-uptake blocker).
- Conversely, ketanserin (a 5-HT receptor antagonist) mitigated the TRP responses.
- All five amines studied were found to displace 5-HT from platelets, with TYR exhibiting the highest potency, followed by TRP, PEA, IAA, and IBA.
Conclusions
- The amine substances from the horse’s cecum were found to trigger constriction of the digital blood vessels. More specifically, TRP and TYR brought about significant venoconstrictions.
- The study also discovered that TYR activated alpha-adrenoceptors (by releasing neuronal norepinephrine) and TRP activated 5-HT receptors.
- Each of the amines tested caused release of 5-HT from platelets.
- The research indicates that these amines, which are formed in the cecum and later released into the bloodstream, deserve further examination as potential factors triggering digital ischemia and laminitis in horses.
Cite This Article
APA
Elliott J, Berhane Y, Bailey SR.
(2003).
Effects of monoamines formed in the cecum of horses on equine digital blood vessels and platelets.
Am J Vet Res, 64(9), 1124-1131.
https://doi.org/10.2460/ajvr.2003.64.1124 Publication
Researcher Affiliations
- Department of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Royal College St, London NW1 0TU, UK.
MeSH Terms
- Adrenergic alpha-Agonists / pharmacology
- Animals
- Biogenic Amines / blood
- Biogenic Amines / metabolism
- Biogenic Amines / pharmacology
- Blood Platelets / drug effects
- Blood Platelets / metabolism
- Cecum / drug effects
- Cecum / metabolism
- Cystamine / analogs & derivatives
- Cystamine / pharmacology
- Femoral Artery / drug effects
- Femoral Artery / metabolism
- Femoral Artery / physiology
- Femoral Vein / drug effects
- Femoral Vein / metabolism
- Femoral Vein / physiology
- Fluoxetine / analogs & derivatives
- Fluoxetine / pharmacology
- Horses / blood
- In Vitro Techniques
- Isometric Contraction / drug effects
- Isometric Contraction / physiology
- Ketanserin / pharmacology
- Male
- Muscle, Smooth, Vascular / drug effects
- Muscle, Smooth, Vascular / metabolism
- Muscle, Smooth, Vascular / physiology
- Platelet Activation / drug effects
- Platelet Activation / physiology
- Serotonin Antagonists / pharmacology
- Vasoconstriction / drug effects
- Vasoconstriction / physiology
Citations
This article has been cited 5 times.- Paley EL. Diet-Related Metabolic Perturbations of Gut Microbial Shikimate Pathway-Tryptamine-tRNA Aminoacylation-Protein Synthesis in Human Health and Disease. Int J Tryptophan Res 2019;12:1178646919834550.
- Menzies-Gow NJ, Wray H, Bailey SR, Harris PA, Elliott J. The effect of tumour necrosis factor-α and insulin on equine digital blood vessel function in vitro. Inflamm Res 2014 Aug;63(8):637-47.
- Haritou SJ, Zylstra R, Ralli C, Turner S, Tortonese DJ. Seasonal changes in circadian peripheral plasma concentrations of melatonin, serotonin, dopamine and cortisol in aged horses with Cushing's disease under natural photoperiod. J Neuroendocrinol 2008 Aug;20(8):988-96.
- Delesalle C, Deprez P, Schuurkes JA, Lefebvre RA. Contractile effects of 5-hydroxytryptamine and 5-carboxamidotryptamine in the equine jejunum. Br J Pharmacol 2006 Jan;147(1):23-35.
- Llada IM, Lourenco JM, Dycus MM, Carpenter JM, Jarrell ZR, Jones DP, Suen G, Hill NS, Filipov NM. Impact of Low-Level Ergot Alkaloids and Endophyte Presence in Tall Fescue Grass on the Metabolome and Microbiome of Fall-Grazing Steers. Toxins (Basel) 2025 May 17;17(5).
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