Endothelium-dependent vasoactive modulation in the ophthalmic circulation

The vascular endothelium is strategically located between the circulating b lood and the vascular smooth muscle cells. Different agonists or stimuli tr ansported by the circulating blood can trigger the endothelium to release p otent relaxing (nitric oxide, prostacyclin. endothelium-derived hyperpolari zing factor) or contracting factors (endothelin, cycloxygenase products). T hese endothelium-derived vasoactive factors can modulate blood flow locally . Heterogeneity exists from one vascular bed to the other. or even between vessels, in the agonists able to stimulate the release of endothelium-deriv ed vasoactive factors. In the ophthalmic circulation, nitric oxide and endo thelin are strong vasoactive modulators. In many vascular diseases that are of importance in ophthalmology (hypercholesterolemia. arteriosclerosis, hy pertension, diabetes, vasospastic syndrome. ischemia and reperfusion. etc) the function of the endothelium can be impaired. There exist different drug s that can modulate the vasoactive function of the vascular endothelium. In other words, it appears that the vascular endothelium plays an important r ole in both the physiology and pathophysiology of the regulation of blood f low. The modulation of this regulatory system by different drugs might open new therapeutical approaches to treat vascular disorders in ophthalmology. (C) 1001 Elsevier Science Ltd. All rights reserved.