Characterization and comparison of the responses of equine digital arteries and veins to endothelin-1.

This research compares the responses of equine digital arteries (EDAs) and equine digital veins (EDVs) in horses to the hormone endothelin-1 (ET-1). The study observes that ET-1 causes vasoconstriction (narrowing of blood vessels) in both types of vessels, but veins are more sensitive. The effect is mediated primarily by ETA receptors and is not significantly influenced by the presence of the endothelium, the inner lining of the blood vessels.

Materials and Methods

• The study used 5 to 9 palmar digital vessels per experiment obtained from 28 healthy horses. These vessels were either arteries (EDAs) or veins (EDVs).
• Vessel segments were prepared and tension was maintained using force transducer wires in organ baths filled with a biological solution called Krebs-Henseleit solution at 30 degrees Celsius.
• The study examined the response of the vessels to various concentrations of ET-1. Both endothelium-intact (+e) and endothelium-denuded (-e) versions of the vessels were used to understand the role of the endothelium in the response.
• Receptor-specific experiments were also conducted where vessels were precontracted with a compound (U44069) and then exposed to an ETB receptor agonist (S6c). Additionally, the effect of ETA and ETB receptor antagonists (BQ-123 and BQ-788 respectively) on the responses to ET-1 was also assessed.

Results

• Endothelin-1 caused a concentration-dependent contraction in both the EDAs and EDVs. This vasoconstriction effect was more pronounced in the veins (EDVs).
• Neither type of vessel relaxed in response to S6c, indicating that ETB receptors may not play a significant role in these responses.
• When the vessels were treated with BQ-123, an ETA receptor antagonist, the responses to ET-1 were inhibited. However, BQ-788, an ETB receptor antagonist had no such effect, reinforcing that the results are primarily mediated by ETA receptors.

Conclusions

• This study suggests that ET-1 can induce notable vasoconstriction within equine digital veins. This effect was found to be predominantly mediated through ETA receptors and was not largely influenced by the presence or absence of the endothelium.
• The findings are important as they could help understand certain vascular diseases in horses, particularly those that involve the narrowing of blood vessels.