As vasodilators, apelin agonists acts as functional antagonists of endothelin mediated vasoconstriction (Maguire et al., 2009), where endothelin peptide (ET-1) levels are known to be elevated in hypoxic states (Grimshaw, 2007) and in PAH patients (Giaid et al., 1993). The gene discussed is APLN; the disease is pulmonary arterial hypertension.