TPH1 and pulmonary arterial hypertension: In both patients with PH and in animal models of PH, pulmonary endothelial TPH1 expression is increased.9,11 There is growing evidence that genetic ablation of TPH1 or pharmacological inhibition can protect against or reverse experimental PH including in the hypoxic, monocrotaline, dexfenfluramine, and sugen/hypoxic animal models.11,29,74,83, , –86 This has led to recent interest in the use of TPH1 inhibitors for the treatment of PAH patients.