Because ET-1 is a very powerful vasoconstrictor and has been shown to be of special importance in the pathophysiology of PAH (Chester and Yacoub, 2014) we pre-constricted mouse pulmonary vessels with ET-1 (3 × 10−9 M) and then increasing concentrations of FR or the drugs mentioned above were applied at similar concentrations (10−9 M–10−5 M). The gene discussed is EDN1; the disease is pulmonary arterial hypertension.