EDN1 and chronic obstructive pulmonary disease: The causes are the hypoxic vasoconstriction of the pulmonary vascular bed, the inflammatory situation of COPD which in the lungs would lead to such a fibrotic damage to increase vascular resistance, the toxic effects of cigarette smoking, and, finally, an imbalance between the concentrations of endothelin 1 (ET-1) and nitric oxide (NO) which promotes vasoconstriction [17].