Determination of the source of increased serotonin (5-HT) concentrations in blood and peritoneal fluid of colic horses with compromised bowel.
BACKGROUND
Increased plasma (5-HT) concentrations are reported in horses predisposed to develop laminitis and after i.v. infusion of endotoxins. In the equine jejunum contractile 5-HT1A-like receptors show tachyphylaxia upon prolonged activation with 5-HT. Therefore, increased systemic 5-HT release in colic horses could play a possible role in the pathophysiology of ileus.


OBJECTIVE
To investigate possible increased systemic release of 5-HT in colic horses with compromised bowel and to identify the source of 5-HT overload.


METHODS
Concentrations of 5-HT were determined in plasma and peritoneal fluid (PF) of healthy horses (n = 10), strangulating small intestinal colic horses (n = 18), nonsurgical colic horses (n = 10) and cryptorchid stallions (n = 6). It was attempted to identify the source of 5-HT overload by comparing the blood and PF 5-HT concentrations within horses and by assessing the in vivo platelet activation through determination of the beta-thromboglobulin (beta-TG)/platelet factor 4 (PF4) ratio.


RESULTS
All horses in the strangulating small intestinal colic group had plasma (P = 0.006) and PF (P = 0.01) 5-HT concentrations above those found in the control group. Plasma beta-TG/PF4 ratio in these horses exceeded 2 in all cases, indicating in vivo platelet activation. Concentrations of 5-HT in PF of colic horses with compromised bowel were significantly lower than the corresponding plasma concentrations (P = 0.005).


CONCLUSIONS
In horses with compromised bowel, significant amounts of 5-HT can be released into the systemic circulation, through massive release of platelet-stored 5-HT. 5-HT is a very potent proinflammatory, vasoconstrictive and immunomodulatory agent. In view of the rapid and prolonged tachyphylaxia, shown for the jejunal 5-HT1A-like receptors, this increased systemic 5-HT release could play a role in the pathophysiology of ileus in horses.
Delesalle
C
C
Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
van de Walle
G R
GR
Nolten
C
C
Ver Donck
L
L
van Hemelrijck
A
A
Drinkenburg
W
W
de Bosschere
H
H
Claes
P
P
Deprez
P
P
Lefere
L
L
Torfs
S
S
Lefebvre
R A
RA
D000818:Animals; D001202:Ascitic Fluid / Q000737:chemistry* / Q000378:metabolism; D015415:Biomarkers / Q000097:blood / Q000378:metabolism; D016022:Case-Control Studies; D003085:Colic / Q000097:blood / Q000378:metabolism / Q000601:surgery / Q000662:veterinary*; D005260:Female; D006734:Horse Diseases / Q000097:blood / Q000378:metabolism* / Q000601:surgery; D006736:Horses; D045823:Ileus / Q000097:blood / Q000378:metabolism / Q000601:surgery / Q000662:veterinary*; D008297:Male; D015539:Platelet Activation; D011183:Postoperative Complications / Q000662:veterinary; D012701:Serotonin / Q000097:blood / Q000378:metabolism*
D015415:Biomarkers; D012701:Serotonin