Predisposition for venoconstriction in the equine laminar dermis: implications in equine laminitis.
Authors: Peroni, Moore, Noschka, Grafton, Aceves-Avila, Lewis, Robertson
Journal: Journal of applied physiology (Bethesda, Md. : 1985)
Summary
# Editorial Summary The early stages of laminitis involve microvascular dysfunction, yet the specific vascular physiology of the equine laminar bed has remained poorly characterised until now. Peroni and colleagues examined how laminar arteries and veins responded to four key vasoconstrictor substances (phenylephrine, serotonin, prostaglandin F2α, and endothelin-1) using isolated vessel preparations, measuring the concentration required to trigger contraction and achieve 50% maximal response (EC50 values). Laminar veins demonstrated substantially greater sensitivity to all four agonists—requiring roughly 8–1,000 times lower concentrations than arteries to initiate contraction—and produced maximal contractile responses that exceeded those of arteries when compared relative to potassium depolarisation. These findings reveal a fundamental physiological predisposition towards venoconstriction in the digital vasculature, a trait potentially protective during exercise but potentially pathological when triggered inappropriately during systemic disease. For practitioners managing laminitis cases, this research provides mechanistic insight into why diverse triggering conditions (endotoxaemia, grain overload, sepsis) converge on a common vascular crisis, and highlights the venous system as a critical but often overlooked component of laminitis pathogenesis—a consideration that may inform future therapeutic strategies targeting microvascular dysfunction.
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Practical Takeaways
- •Understanding the enhanced venoconstrictor sensitivity in laminar vasculature helps explain why laminitis can develop secondary to diverse systemic conditions—this isn't just an arterial problem.
- •The heightened responsiveness of laminar veins to endothelin-1 and other vasoconstrictors suggests that conditions triggering these mediators (endotoxemia, pain, stress) may have particular relevance to laminitis development.
- •Exercise-induced blood flow changes may be more dependent on venous control in the digit than previously appreciated, with implications for understanding why laminitis sometimes develops after work or stress.
Key Findings
- •Laminar veins demonstrated greater sensitivity to all four vasoconstrictor agonists tested (phenylephrine, 5-HT, PGF2α, endothelin-1) compared to laminar arteries, requiring lower concentrations to achieve EC50 values.
- •Endothelin-1 showed the most dramatic difference with EC50 of 467±38 pM for veins versus 70.6±6.4 nM for arteries (150-fold difference).
- •Maximal contractile responses of laminar veins exceeded those of laminar arteries for each agonist when normalized to potassium-induced depolarization.
- •A physiological predisposition for venoconstriction in equine laminar vasculature may explain the varied pathological triggers of laminitis and have implications for blood flow regulation during exercise.