Thus, in this in vitro study, we have characterized the drugs currently approved for PAH (except for ET-1 antagonists as discussed below), other agents that could be useful as potential therapies or drugs targeting major vasodilator pathways in order to compare: (1) their efficacy to relax pulmonary vessels compared to systemic arteries (pulmonary selectivity), and (2) whether their vasodilator effects are modified by the oxygen levels (oxygen selectivity). This evidence concerns the gene EDN1 and pulmonary arterial hypertension.