EDN1 and pulmonary arterial hypertension: ET-1 activity is significantly increased in different rat pulmonary hypertension models, including hypoxic pulmonary hypertension rats, monocrotaline-induced pulmonary hypertension rats, and genetically modified pulmonary hypertension rats.61, 62, 63, 64 Moreover, the ability to clear ET-1 from circulation was impaired in experimental pulmonary hypertension models and the lungs of patients with pulmonary hypertension.65