Endothelium and responsiveness of vascular smooth muscle

The endothelium of a wide variety of arteries can release a potent vasodilator substance (endothelium-derived relaxing factor). The relaxation of smooth muscle cells evoked by endothelium-derived relaxing factor is associated with activation of guanylate cyclase. Under certain conditions the endothelium can produce contracting factors as well. Dysfunction of the endothelium may lead to abnormal behaviour of the underlying smooth muscle, e.g. vasospasm.