Through immunohistochemical staining of PHD2 and HIF1α in the pulmonary tissues of PAH model rats, we found that PHD2 expression was decreased in pulmonary tissues of PAH model rats, while HIF1α expression was markedly elevated, which was reversed by AS-IV administration (Fig. 4A, B, C and D). This evidence concerns the gene EGLN1 and pulmonary arterial hypertension.