EDNRA and pulmonary arterial hypertension: Patients diagnosed with PAH have increased activation of ET-1 in both plasma and lung tissues (Galié et al., 2004) and elevated plasma levels of ET-1 can be correlated with severity of disease and prognosis (McLaughlin et al., 2009), leading to the exploration of various compounds capable of blocking either ETA or ETA and ETB receptors.