Endotoxin-induced digital vasoconstriction in horses: associated changes in plasma concentrations of vasoconstrictor mediators.
BACKGROUND
Lipopolysaccharide (LPS) infusion reduces digital perfusion, but the mediators responsible remain undetermined.


OBJECTIVE
To identify vasoconstrictor mediators released following LPS infusion and relate their appearance in plasma to digital blood flow alterations.


METHODS
Blood flow in the lateral digital vessels of 6 Thoroughbred horses, following a 30 min infusion of LPS (E. coli 055:B5; 30 ng/kg), was measured using Doppler ultrasonography. Concomitant measurements of hoof wall and coronary band surface temperatures (HWST and CBST) were made. Serial blood samples were collected and plasma LPS, tumour necrosis factor alpha (TNFalpha), 5-HT, thromboxane B2 (TxB2) and endothelin measured.


RESULTS
Plasma LPS concentrations reached a maximum of 13.2 pg/ml during the infusion, followed by an increase in plasma TNFalpha concentration. Digital arterial and venous blood flow decreased by 43 and 63%, respectively; HWST and CBST similarly decreased. Systemic blood pressure remained unaltered. Plasma concentrations of TxB2 and 5-HT increased, coinciding with the onset of digital hypoperfusion. Plasma endothelin concentrations remained unchanged.


CONCLUSIONS
The temporal relationship between the onset of digital hypoperfusion and increases in plasma 5-HT and TxB2 concentrations is consistent with these platelet-derived mediators being associated with LPS-induced laminitis.


CONCLUSIONS
These experimental data support the use of anti-platelet therapy in the prevention of laminitis associated with endotoxaemic conditions.
Menzies-Gow
N J
NJ
Department of Veterinary Clinical Sciences, Royal Veterinary College, Hatfield, Hertfordshire AL9 7TA, UK.
Bailey
S R
SR
Katz
L M
LM
Marr
C M
CM
Elliott
J
J
D000818:Animals; D001831:Body Temperature; D016232:Endothelins / Q000097:blood; D005260:Female; D005534:Foot Diseases / Q000097:blood / Q000517:prevention & control / Q000662:veterinary; D006724:Hoof and Claw / Q000098:blood supply* / Q000000981:diagnostic imaging; D006734:Horse Diseases / Q000097:blood / Q000517:prevention & control; D006736:Horses; D007249:Inflammation / Q000097:blood / Q000517:prevention & control / Q000662:veterinary; D007262:Infusions, Intravenous / Q000662:veterinary; D008070:Lipopolysaccharides / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D008297:Male; D011897:Random Allocation; D012039:Regional Blood Flow / Q000187:drug effects; D012701:Serotonin / Q000097:blood; D013929:Thromboxane B2 / Q000097:blood; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D018608:Ultrasonography, Doppler / Q000662:veterinary; D014661:Vasoconstriction / Q000187:drug effects*
D016232:Endothelins; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D012701:Serotonin; D013929:Thromboxane B2