Endothelin-1, a potent vasoconstrictor and mitogen for smooth muscle cells produced by endothelial cells, has been found to have elevated plasma levels in patients with both Idiopathic Pulmonary Arterial Hypertension (IPAH) and Chronic Thromboembolic Pulmonary Hypertension (CTEPH) (64). Here, EDN1 is linked to idiopathic pulmonary arterial hypertension.