Endothelial dysfunction in hypertension: fact or fancy?

Endothelium can deeply influence vascular tone and structure. The main endothelium-derived factor is nitric oxide (NO), which not only is a potent vasodilator but also inhibits platelet aggregation, smooth muscle cell proliferation, monocyte adhesion, and adhesion molecule expression, thus protecting the vessel wall against the development of atherosclerosis and thrombosis. In human hypertension, endothelial dysfunction has been documented in peripheral and coronary macro- and microcirculation and in renal circulation. Impaired endothelium-dependent vasodilatation associated with essential hypertension appears to be a primary phenomenon because it can be detected in the offspring of essential hypertensive patients, shows no clear correlation with blood pressure value, and is not normalized by the mere reduction of blood pressure. The phenomenon responsible for endothelial alteration in essential hypertensive patients appears to be the activation of an alternative pathway involving cyclo-oxygenase (COX), which reduces NO availability through production of oxidative stress. This alteration in the NO pathway could be the main mechanism through which a dysfunctional endothelium may promote atherosclerosis and thrombosis in essential hypertension. Therefore, an important aim of antihypertensive therapy would be not only to normalize blood pressure values but also to reverse endothelial dysfunction by restoring NO availability. Evidence indicates that different classes of antihypertensive compounds have different effects on this alteration. Dihydropiridine calcium antagonists appear to act specifically on the NO pathway by a mechanism that is probably related to antioxidant activity.