ENDOTHELIN (ET)-1 AND ITS RECEPTORS (ETA AND ETB) MEDIATE A VARIETY OF DELETERIOUS EFFECTS, SUCH AS VASOCONSTRICTION, FIBROSIS, PROLIFERATION, HYPERTROPHY, AND INFLAMMATION. IN DISEASE CONDITIONS SUCH AS PAH, THE LOCAL ET SYSTEM IS UPREGULATED AND IS INVOLVED IN VASCULAR HYPERTROPHY AND IN ORGAN DAMAGE.