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

This research aimed to understand the effects of a specific type of toxin exposure on the vascular responses in horses, particularly related to laminitis, a painful hoof condition. Specifically, the study explored how the exposure to a toxin from a bacteria strain (Escherichia coli O55:B5) affected the way blood vessels in the horse’s forelimbs responded to various stimuli.

Methodology

• The experiment involved 11 healthy horses undergoing two surgical procedures with a 3-week gap in between. The second surgery was preceded by a controlled administration of a specific strain of bacteria (0.25 microg/kg of lipopolysaccharide from Escherichia coli O55:B5) to simulate a toxin exposure.
• The research focused on analyzing the reactivity or response of the arteries and veins in the horses’ forelimbs to certain substances, post the bacterial exposure. Samples were extracted during the surgeries for laboratory testing.
• The substances tested in the laboratory included depolarizing Krebs solution (DKS), phenylephrine (PHE), acetylcholine (ACh), and sodium nitroprusside (SNP), all known for their distinctive effects on vascular tissues (blood vessels). Response to these substances was gauged through in vitro experiments.

Findings

• All the horses exhibited symptoms of pain, excessive bowel movements, increased heart rate and breathing rate, temperature rise, and a decrease in white blood cells, suggestive of an acute toxic reaction.
• The study provided evidence that toxin exposure has different impact on the reactivity of arteries and veins. The reactivity of the arterial tissues to phenylephrine increased while no notable changes were observed in the veins.
• Moreover, the reactivity of both arteries and veins to acetylcholine decreased, yet there were no significant differences in their reactions to sodium nitroprusside and the depolarizing Krebs solution.
• Despite these changes in the reaction patterns, no histopathological changes (tissue changes visible under a microscope) were observed.

Implications

• The findings confirm that endotoxemia or toxin exposure causes changes in the vascular reactivity of horses in its acute phase.
• This change in vascular reactivity, particularly the reduction in vasodilatory capacity (ability to widen blood vessels) and endothelial function impairment (inability of the inner lining of blood vessels to function properly), indicates an increased potential for the development of a prothrombotic state (increased risk of blood clot formation) in the blood vessels of horses’ limbs.
• These results provide insights into the potential links between endotoxemia and the development of laminitis, highlighting the need for greater attention to infection control in equine healthcare.