EDN1 and pulmonary arterial hypertension: Presently approved PAH drugs target one of the three major pathways involved in PAH pathogenesis: the prostacyclin, endothelin-1, and NO pathways.[18] All PAH drugs have vasodilatory properties and also variable antiproliferative effects on the pulmonary vasculature.[19] However, data on the use of PAH therapy in PVOD are weak and conflicting.