“…Since then, the characterization of numerous chemical and physical stimuli that induce endotheliumdependent relaxation, 4 followed by the identification of one of the "endothelium-dependent relaxing factors," such as nitric oxide (NO) or a closely related nitroso compound, 5 has made the investigation of the endothelial function one of the most exciting fields in current cardiovascular research. 6 Substantial data are now available which demonstrate that, in addition to mediating vasodilatation, 405 endothelium can also facilitate contractile responses of the vascular smooth muscle. 7 Various chemical and mechanical factors, including noradrenaline, thrombin, neuropeptide Y, calcium ionophoreA23187, arachidonic acid, hypoxia, stretch, and increased transmural pressure, have been found to cause vasoconstriction, dependent on an intact endothelium.…”