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Seasonal changes in plasma concentrations of cecum-derived amines in clinically normal ponies and ponies predisposed to laminitis

Simon R. BaileyDepartment of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Royal College St, London NW1 0TU, UK.

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 BVMS, PhD
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Lisa M. KatzDepartment of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Royal College St, London NW1 0TU, UK.

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 DVM, MS
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Yoel BerhaneDepartment of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Royal College St, London NW1 0TU, UK.

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 BSc
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Tim SamuelsThe Horseracing Forensic Laboratory, Newmarket Rd, Fordham, Newmarket, Cambridgeshire, CB7 5WW, UK.
Present address is Clinical Trials BioResearch Ltd, 87 Senneville Rd, Senneville, QC H9X 3R3, Canada.

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Nicholas De BrauvereRedwings Horse Sanctuary, Hapton Hall Farm, Hapton, Norfolk, NR15 1SP, UK.

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Celia M. MarrDepartment of Veterinary Clinical Sciences, The Royal Veterinary College, University of London, Royal College St, London NW1 0TU, UK.

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Jonathan ElliottDepartment of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Royal College St, London NW1 0TU, UK.

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 Vet MB, PhD

Abstract

Objective—To measure concentrations of amines formed in the cecum of clinically normal ponies, determine amine concentrations in plasma samples collected in spring and winter, and compare concentrations of amines and serotonin in plasma samples obtained from clinically normal ponies and ponies predisposed to laminitis.

Sample Population—Cecal contents obtained from 10 ponies euthanatized at an abattoir and blood samples obtained from 42 adult ponies.

Procedure—Cecal contents were assayed for amines by high-performance liquid chromatography (HPLC). Blood samples were collected at various times of the year from 20 ponies predisposed to acute laminitis and 22 clinically normal ponies. Plasma serotonin concentration was measured by HPLC, and tryptamine (TRP), tyramine (TYR), phenylethylamine (PEA), and isoamylamine (IAA) were measured by liquid chromatography- mass spectrometry.

Results—15 amines were identified in cecal contents. Plasma TRP, TYR, PEA, and IAA concentrations ranged from 10pM to 100nM in both groups of ponies. Plasma concentrations of serotonin or other amines did not differ between clinically normal ponies and those predisposed to laminitis; however, significantly higher concentrations of TRP, PEA, and IAA were found in samples obtained in the spring, compared with winter samples.

Conclusions and Clinical Relevance—Various amines are found in the cecum of ponies, several of which can be detected in the plasma. Concentrations increase significantly in the spring and may reach concentrations close to the threshold for causing vasoconstriction. Release of amines from the cecum into the systemic circulation may contribute to hemodynamic disturbances in horses and ponies with acute laminitis. (Am J Vet Res 2003;64:1132–1138)

Abstract

Objective—To measure concentrations of amines formed in the cecum of clinically normal ponies, determine amine concentrations in plasma samples collected in spring and winter, and compare concentrations of amines and serotonin in plasma samples obtained from clinically normal ponies and ponies predisposed to laminitis.

Sample Population—Cecal contents obtained from 10 ponies euthanatized at an abattoir and blood samples obtained from 42 adult ponies.

Procedure—Cecal contents were assayed for amines by high-performance liquid chromatography (HPLC). Blood samples were collected at various times of the year from 20 ponies predisposed to acute laminitis and 22 clinically normal ponies. Plasma serotonin concentration was measured by HPLC, and tryptamine (TRP), tyramine (TYR), phenylethylamine (PEA), and isoamylamine (IAA) were measured by liquid chromatography- mass spectrometry.

Results—15 amines were identified in cecal contents. Plasma TRP, TYR, PEA, and IAA concentrations ranged from 10pM to 100nM in both groups of ponies. Plasma concentrations of serotonin or other amines did not differ between clinically normal ponies and those predisposed to laminitis; however, significantly higher concentrations of TRP, PEA, and IAA were found in samples obtained in the spring, compared with winter samples.

Conclusions and Clinical Relevance—Various amines are found in the cecum of ponies, several of which can be detected in the plasma. Concentrations increase significantly in the spring and may reach concentrations close to the threshold for causing vasoconstriction. Release of amines from the cecum into the systemic circulation may contribute to hemodynamic disturbances in horses and ponies with acute laminitis. (Am J Vet Res 2003;64:1132–1138)