EDN1 and pulmonary arterial hypertension: The main pathogenetic mechanisms in SSc-PAH are thought to be endothelial dysfunction and impaired balance between vasoconstrictor and vasodilator mediators such as endothelin-1 (ET-1), nitric oxide (NO), prostacyclin (PG-I2), and smooth muscle proliferation leading to vasculopathy [4, 5].