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The endothelium is a source of vasoactive factors among which the most relevant are nitric oxide and endothelin. Nitric oxide is synthesized from L-arginine by a family of nitric oxide synthases and is a widespread biological mediator. It is implicated in many physiological and pathophysiological processes, including a variety of cardiovascular diseases like hypertension.The release of nitric oxide seems to be modulated by changes in blood pressure. However, the role of nitric oxide in hypertension is still controversial and seems to vary depending on the stage of the disease and the model studied. In spontaneous hypertension, the production of nitric oxide is increased but inefficacious, probably because of increased inactivation or scavenging. In the heart the production of nitric oxide seems to be increased, probably as a compensatory mechanism against hypertension, in salt-induced hypertension, nitric oxide production may be impaired. In human hypertension, pharmacological experiments reveal an impaired nitric oxide dilator mechanism. In pulmonary hypertension, the use of nitric oxide gas inhalation has been proposed as a future therapy for this condition.Endothelin-1 is a potent vasoconstrictor peptide produced and released from endothelial cells. In isolated blood vessels, endothelin causes profound contraction. The hemodynamic effects of endothelin can be explained by the activation of two endothelin receptors, ETA and ETB. The relationship between endothelin and hypertension is not clear. Although plasma endothelin levels are normal in most patients with essential hypertension, the hypertensive blood vessel wall may contract more profoundly in response to the peptide; hence, endothelin antagonists may have antihypertensive effects in patients with hypertension.