Experiments were designed to study endothelium-dependent relaxations in human renal arteries (N = 13) and peripheral arteries (N = 8) suspended in organ chambers for isometric tension recording. In contracted arterial rings, acetylcholine caused endothelium-dependent relaxations that were not inhibited by indomethacin in either artery but were significantly augmented in the renal artery. Adenosine diphosphate and thrombin caused endothelium-dependent relaxations in renal but not in peripheral arteries. This finding suggests a heterogeneity of endothelium-dependent relaxations in human arteries and indicates that the relaxations are mediated by the release of an endothelium-derived relaxing factor (or factors) rather than the release of prostacyclin.
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