Effect of acute sublethal endotoxaemia on in vitro digital vascular reactivity in horses

Endotoxaemia is a syndrome linked to the development of equine laminitis; however, the relationship between them is uncertain. The aim of this experiment was to evaluate the effect of an experimental acute sublethal endotoxaemia model on in vitro equine palmar digital vascular reactivity. Rings of arteries and veins of each forelimb were obtained from 11 clinically healthy horses submitted to two surgical procedures, 3 weeks apart. Before the second surgery, 0.25 microg/kg of lipopolysaccharide from Escherichia coli O55:B5 in saline, was administered i.v. in 30 min. After 3 h, the vessels were harvested and submitted to in vitro vascular reactivity experiments and histopathology. The response to depolarizing Krebs solution (DKS, 40 mm), phenylephrine (PHE), acetylcholine (ACh) and sodium nitroprusside (SNP) were evaluated. All horses showed colic pain and watery diarrhoea, tachycardia, tachypnea, hyperthermia and leucopenia. Concentration-response curve (CRC) to PHE was shifted to the left in arteries rings from endotoxemic horses without any effect on vein rings. The CRC to ACh was shifted to the right with a reduction in the maximal response. The response to SNP and DKS was similar between groups. There was no evidence of histopathological effects. The increased response to PHE in digital arteries together with a reduction of the endothelium-dependent response to ACh in arteries and veins, confirm the existing reports where endotoxaemia was found to modify the digital vascular reactivity during the acute phase. As the digital endothelial function is impaired, there may be an increased potential to develop a digital prothrombotic state with a reduced vasodilatory capacity.