Endothelin-1 is a potent endogenous vasoconstrictor that is overexpressed in the pulmonary vasculature of PAH patients and can cause pulmonary vasoconstriction, promote cell mitosis, and contribute to the development and progression of PAH by binding to endothelin receptors A and B in pulmonary vascular smooth muscle cells. This evidence concerns the gene EDN1 and pulmonary arterial hypertension.