Equine laminitis: ultrastructural lesions detected in ponies following hyperinsulinaemia.
Authors: Nourian A R, Asplin K E, McGowan C M, Sillence M N, Pollitt C C
Journal: Equine veterinary journal
Summary
# Equine Laminitis and Hyperinsulinaemia: Ultrastructural Changes in the Lamellae Prolonged elevation of circulating insulin causes distinct microscopic damage to hoof lamellar tissue that differs markedly from carbohydrate-induced laminitis, according to this 2009 investigation using transmission electron microscopy in clinically lame ponies. Five insulin-treated ponies and four saline controls were examined following an euglycaemic hyperinsulinaemic clamp protocol; treatment animals developed Obel grade II clinical laminitis whilst control tissue was collected at 72 hours. The key ultrastructural findings included elongated and attenuated lamellae with increased epidermal basal cell mitosis, sporadic basement membrane separation localised near infiltrating leucocytes (rather than global separation seen in carbohydrate-induced disease), thickened lamellar basement membranes in two animals, and significantly reduced hemidesmosomal density across all treated ponies. These changes suggest that insulin acts as a mitogenic stimulus, driving aberrant cellular proliferation that mechanically weakens the dermal-epidermal attachment and contributes to clinical lameness. For practitioners managing insulin-resistant or hyperinsulinaemic horses and ponies, this work emphasises the importance of pharmaceutical and dietary insulin control; managing circulating insulin concentrations may directly ameliorate the progressive lamellar pathology rather than simply treating secondary inflammation.
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Practical Takeaways
- •Hyperinsulinaemia alone can induce laminitis through a distinct pathological mechanism; medical management of insulin resistance should be a priority in at-risk ponies and horses before clinical lameness develops
- •The lesions produced by hyperinsulinaemia differ significantly from carbohydrate-induced laminitis, suggesting different treatment and prevention strategies may be required
- •Early intervention targeting insulin control may prevent or ameliorate the lamellar changes before they progress to clinical grades of laminitis
Key Findings
- •Prolonged hyperinsulinaemia induced attenuated and elongated lamellae with increased epidermal basal cell mitosis in 5 treated ponies, without the global dermal-epidermal separation characteristic of carbohydrate-induced laminitis
- •Sporadic basement membrane separation occurred in association with infiltrating leucocytes, and hemidesmosome density was significantly decreased in all insulin-treated ponies
- •Lamellar basement membrane was thickened in 2 of 5 insulin-treated ponies, suggesting variable pathological responses to hyperinsulinaemia
- •Insulin-induced lamellar proliferation and aberrant mitosis may weaken the lamellar-distal phalanx attachment apparatus, contributing to clinical laminitis signs