TPH1 and pulmonary arterial hypertension: In addition to sustained increases in PDGF‐β and the TGF‐β1 pathway components, Nox‐4 and PAI‐1, we observed transient increases in VEGF, TPH‐1, and IL‐6, mediators associated with de‐regulated proliferation of activated microvascular endothelial cells and formation of plexiform lesions in primary PAH.