Endothelium-derived relaxing factor is an endogenous vasodilator in man.

Removal of venous endothelium in man leads to vasoconstriction and loss of dilator response to acetylcholine but not to glyceryl trinitrate. This pattern of responses can be accounted for by loss of endothelium-derived relaxing factor (EDRF), but not by loss of prostacyclin. This provides the first direct evidence for endothelium-dependent dilatation in man in vivo, and suggests that basal release of EDRF is a determinant of resting venous tone.