Evidence for endothelium-derived relaxing factor/nitric oxide in equine digital arteries.

OBJECTIVE

To test the hypothesis that endothelium-derived nitric oxide modulates vasomotor reactivity in equine digital arteries.

DESIGN

Digital arteries were isolated from adult horses, and their vasodilator properties were examined in an in vitro controlled environment.

ANIMALS

Five adult horses (1 gelding, 4 mares) without evidence of hoof or vascular disease were studied.

PROCEDURE

Arterial rings with or without endothelium were exposed to endothelium-dependent vasodilator drugs in the presence or absence of a pharmacologic inhibitor of the enzyme nitric oxide synthase.

RESULTS

Vasodilator effects of 3 endothelium-dependent vasorelaxant agents were significantly greater in endothelium-intact vessels than in endothelium-denuded vessels. Moreover, a nitric oxide synthase inhibitor reduced vasodilator responses to endothelium-dependent vasodilators in endothelium-intact arteries, but had no discernable effects in endothelium-denuded arteries.

CONCLUSIONS

These findings indicate the presence of endothelium-derived relaxing factor/nitric oxide in blood vessels of horses, and identify vascular endothelium as an endogenous modulator of vasomotor tone in the digital arteries of this species.