ET-1 exerts its effect through the actions of twoG-protein coupled receptors, ET-A and ET-B, localized on the smooth muscle cells.Expression of ET-1—as well as its associated activating proteases and receptors—is increased in PAH [22], where it directs a program of vasoconstriction andPASMC proliferation (reviewed in [23]). Here, EDN1 is linked to pulmonary arterial hypertension.