Abstract
Objective—To compare the responses of equine digital arteries (EDAs) and equine digital veins (EDVs) to endothelin-1 (ET-1) and determine the role of the endothelium and type of receptors involved in the modulation and mediation of those responses, respectively.
Sample Population—5 to 9 palmar digital vessels/experiment from 28 healthy horses.
Procedure—Rings of dissected vessels were mounted under tension between force transducer wires in organ baths containing Krebs-Henseleit solution at 30oC. Responses of EDAs and EDVs (with intact [+e] or denuded [–e] endothelium) to cumulative concentrations of ET-1 (10–10 to 3 × 10–7 M) were compared. For (+e)EDAs and (+e)EDVs precontracted with a thromboxane-mimetic (U44069; 10–8 M) and (–e)EDAs and (–e)EDVs, responses to an ETB receptor agonist (S6c; 10–10 to 3 × 10–7 M) were evaluated. Responses to ET-1 (10–7 M) in (–e)EDAs and (–e)EDVs were evaluated after incubation with an ETA receptor antagonist (BQ- 123; 3 × 10–7 M), an ETB receptor antagonist (BQ-788; 3 × 10–7 M), or vehicle solution.
Results—Endothelin-1 induced a concentrationdependent contraction of endothelium-intact and -denuded EDAs and EDVs; EDVs were more sensitive. Neither vessel type relaxed in response to S6c, although 2 of the (–e)EDAs contracted mildly. Whereas BQ-123 inhibited the (–e)EDA and (–e)EDV responses to ET-1, BQ-788 had no effect.
Conclusions and Clinical Relevance—Endothelin-1 induced digital vasoconstriction (marked constriction in veins). This action was unaffected by endothelium and mediated predominantly by ETA receptors. These findings suggest ET-1 can induce selective digital venoconstriction. (Am J Vet Res 2003;64:1438–1443
