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

To visualize the endothelial glycocalyx in equine intestinal vessels using electron microscopy and immunohistochemistry and to evaluate the impact of induced endotoxemia on its integrity.

6 healthy horses free of gastrointestinal disease were anesthetized with dexmedetomidine, ketamine, and diazepam and mechanically ventilated under isoflurane anesthesia. Jejunal venous tissue samples were collected after perfusion fixation with lanthanum nitrate before and 120 minutes after endotoxemia induced by IV administration of 30 ng·kg-1 Escherichia coli lipopolysaccharide. For transmission electron microscopy, samples were fixed in lanthanum nitrate solution and embedded in epoxide resin. Additional samples were fixed in formaldehyde, embedded in paraffin, and sectioned for indirect immunohistochemistry to assess heparan sulfate, syndecan-1, catalase, and superoxide dismutase-2 expression.

The endothelial glycocalyx ultrastructure was successfully visualized in 3 of 6 horses. Morphological variations, particularly in glycocalyx thickness (up to 2.5 µm), were observed. Endotoxemia-related alterations indicating structural disruptions were evident in these horses. Immunohistochemical staining for syndecan-1 and superoxide dismutase-2 showed no assessable immunoreactivity, whereas heparan sulfate and catalase immunolabelling were detected on the endothelium.

The endothelial glycocalyx of intestinal vessels was visualized for the first time in horses. Among the tested antibodies, only those against heparan sulfate and catalase demonstrated endothelial reactivity, confirming their presence as components of the equine glycocalyx. Lipopolysaccharides may cause structural disintegrity and loss of glycocalyx.

Visualization of the equine endothelial glycocalyx enhances understanding of vascular pathophysiology in endotoxemic horses. Investigation of the glycocalyx remains technically demanding.