Thermographic study of in vivo modulation of vascular responses to phenylephrine and endothelin-1 by dexamethasone in the horse.
Authors: Cornelisse C J, Robinson N E, Berney C A, Eberhart S, Hauptman J E, Derksen F J
Journal: Equine veterinary journal
Summary
# Editorial Summary Glucocorticoid-induced laminitis has long been suspected to involve enhanced vascular responsiveness in digital tissues, yet this mechanism had never been demonstrated in living horses until this 2006 study. Cornelisse and colleagues used thermographic imaging to measure skin temperature changes following intradermal injection of vasoconstrictor agents in nine horses treated with either dexamethasone (0.1 mg/kg intravenously for six days) or saline in a blinded, crossover design. The dexamethasone-treated horses exhibited significantly reduced baseline skin temperatures—indicating compromised blood flow—alongside a potentiated response to the alpha-1 agonist phenylephrine, evidenced by a leftward shift in the dose-response curve and lower EC50 values; whilst endothelin-1 responses were not directly potentiated, the lower baseline perfusion state resulted in substantially lower absolute skin temperatures after this vasoconstrictor. These findings provide the first in vivo confirmation that glucocorticoids enhance alpha-1 adrenoceptor sensitivity and reduce overall hoof perfusion, a combination particularly concerning when combined with existing hypoperfusion or elevated circulating catecholamines during systemic disease. For practitioners managing horses on glucocorticoid therapy—particularly those with colic, sepsis, or other inflammatory conditions—this research underscores the laminitis risk and argues for careful consideration of dose, duration, and concurrent management strategies aimed at maintaining digital perfusion.
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Practical Takeaways
- •Dexamethasone use in horses reduces hoof blood flow—use cautiously in patients with pre-existing circulatory compromise or laminitis risk
- •During systemic disease with elevated circulating catecholamines, glucocorticoid therapy may compound vasoconstriction and increase laminitis likelihood
- •Monitor hoof temperature and perfusion closely when glucocorticoids are indicated in high-risk patients; consider alternative anti-inflammatory strategies where possible
Key Findings
- •Dexamethasone (0.1 mg/kg) decreased baseline skin temperature, indicating reduced blood flow and increased vasomotor tone
- •Dexamethasone potentiated alpha1-adrenoceptor response to phenylephrine, demonstrated by leftward dose-response curve shift and decreased EC50
- •Dexamethasone did not directly potentiate endothelin-1 response, but combined with lower baseline temperature resulted in significantly lower skin temperatures
- •Glucocorticoid therapy decreases equine hoof perfusion and may increase laminitis risk in disease states already characterized by hypoperfusion or elevated catecholamine levels