The effects of vasoactive amines found in the equine hindgut on digital blood flow in the normal horse.
BACKGROUND
Disturbances of digital blood flow are thought to be fundamental to the pathophysiology of acute laminitis. However, factors linking the initiating events in the equine hindgut with these disturbances in the foot remain to be determined.


OBJECTIVE
Amine compounds, formed by bacteria in the equine hindgut, have digital vasoconstrictor effects in vivo.


METHODS
Tryptamine (1.6 microg/kg/min) and phenylethylamine (2.13 microg/kg/min) were infused i.v. into standing nonsedated horses. Digital blood flow was measured by Doppler ultrasound and foot surface temperature was monitored. Plasma 5-hydroxytryptamine (5-HT) concentrations were measured by HPLC.


RESULTS
Tryptamine and phenylethylamine infusions had no effect on systemic arterial blood pressure or heart rate, but caused significant decreases in digital arterial blood flow (mean +/- s.e. 29.2 +/- 8.5 and 18.4 +/- 6.8%, respectively). Both amines also caused decreases in dorsal hoof wall temperature (0.6 +/- 0.1 and 0.5 +/- 0.1 degrees C for tryptamine and phenylethylamine, respectively) and concomitant increases in plasma 5-HT concentration.


CONCLUSIONS
Tryptamine and phenylethylamine caused reduction of digital blood flow, effects which may have been mediated, in part, via displacement of 5-HT from platelets.


CONCLUSIONS
Amine compounds occurring in the equine hindgut, if released into the circulation following carbohydrate overload, could contribute to selective digital vasoconstriction. Further work in ponies and horses, with naturally occurring laminitis, is necessary to determine whether amines represent a therapeutic target in this disease.
Bailey
S R
SR
Department of Veterinary Basic Sciences, Royal Veterinary College, Hatfield, Hertfordshire AL9 7TA, UK.
Menzies-Gow
N J
NJ
Marr
C M
CM
Elliott
J
J
D000208:Acute Disease; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001831:Body Temperature; D002432:Cecum / Q000098:blood supply / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000662:veterinary; D005260:Female; D005534:Foot Diseases / Q000097:blood / Q000209:etiology / Q000662:veterinary; D006339:Heart Rate / Q000187:drug effects; D006724:Hoof and Claw / Q000098:blood supply* / Q000000981:diagnostic imaging; D006734:Horse Diseases / Q000097:blood / Q000209:etiology; D006736:Horses; D007249:Inflammation / Q000097:blood / Q000209:etiology / Q000662:veterinary; D007262:Infusions, Intravenous / Q000662:veterinary; D008297:Male; D010627:Phenethylamines / Q000008:administration & dosage*; D011897:Random Allocation; D012039:Regional Blood Flow; D012701:Serotonin / Q000097:blood; D014363:Tryptamines / Q000008:administration & dosage*; D018608:Ultrasonography, Doppler / Q000662:veterinary; D014661:Vasoconstriction / Q000187:drug effects*
D010627:Phenethylamines; D014363:Tryptamines; D012701:Serotonin; C030820:tryptamine