Endothelin receptor expression in idiopathic pulmonary arterial hypertension: effect of bosentan and epoprostenol treatment

Endothelin receptor antagonists are used to treat idiopathic pulmonary arterial hypertension (IPAH), but human pulmonary arterial endothelin receptor expression is not well defined. We hypothesised that disease and treatment would modify normal receptor distribution in pulmonary resistance arteries of children. Using immunohistochemistry and semiquantitative analysis, we investigated endothelin receptor subtypes A and B(ETA and ETB, respectively), and endothelial nitricoxide synthase(eNOS) expression in peripheral pulmonary arteries of tissue from untreated children with IPAH(n=7), following extended combined bosentan and epoprostenol therapy (n=5) and from normal subjects (n=5). Clinical, haemodynamic and pathological abnormalities were severe and advanced in all IPAH cases. ETA was detected in pulmonary arterial endothelial cells of all normal and diseased tissue and cultured cells. Endothelial ETA, ETB and eNOS expression was reduced in patent, plexiform and dilatation lesions of untreated cases, but in treated cases, ETA and ETB were normal and eNOS increased. In smooth muscle, ETA expression was reduced in treated cases but ETB expression increased in all arteries of both treated and untreated cases. In summary, ETA is expressed on human pulmonary arterial endothelium. In IPAH, combination treatment with bosentan and epoprostenol had a more marked influence on endothelin receptor expression of endothelial than smooth muscle cells.