In most blood vessels, the endothelium generates both vasodilator and growth-stabilizing
mediators under normal physiological circumstances. The vasodilator influence of the
endothelium modulates the vasoconstriction induced by adrenergic nerves, blood-borne
substances, and local autacoids. Nitric oxide (NO) is a major endothelium-derived
vasodilator, along with protacyclin. A third substance called endothelium-derived
hyperpolarizing factors (EDHF) mediates vasodilatation in certain conduit arteries and in …