In PASMC of four PAH patients, PDGF-BB (1–10 ng/ml) induced TGF-β1 secretion significantly, which was prevented by pre-incubation (30 min) of the cells with treprostinil (10−8–10−6 M) in a concentration dependent manner (Fig 2A). This evidence concerns the gene TGFB1 and pulmonary arterial hypertension.