Endothelial glycocalyx of equine intestinal vessels: electron microscopic and immunohistochemical imaging.

Research Overview

• This study aimed to visualize the endothelial glycocalyx in the intestinal blood vessels of horses and to assess how experimental endotoxemia affects its structure.

Background and Purpose

• The endothelial glycocalyx is a thin, gel-like layer covering the interior surface of blood vessels, playing a key role in vascular health.
• In horses, the glycocalyx in intestinal vessels had not been visualized prior to this study.
• Endotoxemia, or the presence of bacterial toxins in the bloodstream, is known to damage vascular structures, so the study sought to evaluate its impact on the glycocalyx.
• The authors employed advanced imaging techniques—electron microscopy and immunohistochemistry—to observe the glycocalyx at a microscopic level.

Methods

• Six healthy horses (without gastrointestinal disease) were anesthetized using a combination of dexmedetomidine, ketamine, and diazepam, and ventilated with isoflurane to maintain anesthesia.
• Samples of jejunal venous tissue were collected twice per horse: once before and once 120 minutes after inducing endotoxemia through intravenous administration of Escherichia coli lipopolysaccharide (30 ng/kg).
• For electron microscopy visualization:
  • Tissues were perfused and fixed with lanthanum nitrate, then embedded in epoxide resin.
  • Transmission electron microscopy was used to image the ultrastructure of the endothelial glycocalyx.
• For immunohistochemistry:
  • Tissue samples were fixed in formaldehyde, embedded in paraffin, and sliced into thin sections.
  • These sections were stained indirectly with antibodies targeting heparan sulfate, syndecan-1, catalase, and superoxide dismutase-2, which are molecules associated with the glycocalyx or oxidative stress response.

Findings

• The endothelial glycocalyx was successfully visualized by electron microscopy in 3 out of the 6 horses.
• There was noticeable variability in glycocalyx morphology across samples, especially in thickness, which measured up to 2.5 micrometers.
• After inducing endotoxemia, structural disruptions and signs of glycocalyx damage were apparent in the horses where it was visible.
• Immunohistochemistry results showed:
  • No assessable immunoreactivity for syndecan-1 and superoxide dismutase-2 on the endothelium.
  • Positive endothelial immunolabelling for heparan sulfate and catalase, indicating their presence in the equine glycocalyx structure.

Conclusions and Significance

• This research provides the first direct visualization of the endothelial glycocalyx in equine intestinal blood vessels.
• The presence of heparan sulfate and catalase in the glycocalyx was confirmed through immunolabeling.
• Exposure to lipopolysaccharides (endotoxin) can compromise glycocalyx integrity, likely contributing to vascular dysfunction seen in endotoxemia.
• Understanding the glycocalyx in horses helps clarify vascular pathophysiology during endotoxemic conditions such as sepsis, colic, or systemic inflammation.
• However, visualizing the glycocalyx remains technically challenging in equine tissues, indicating the need for further refined methodologies in future research.