STAT5B and pulmonary arterial hypertension: Groups of male and female Wt and STAT5−/− mice were exposed to hypoxia (10% hypobaric oxygen) for 4 weeks or kept under normoxic conditions, and the development of PAH was first evaluated as previously reported (RVSP, ratio of RV/LV + S weights, increased muscularization of vessels, and increased arterial wall thickness) [19].