We have found that niacin prevents the progression of MCT-induced and hypoxia/SU5416-induced PAH in rats and suppresses the development of hypoxia/SU5416-induced PAH in mice by enhancing the expression of H-PGDS in lung tissue macrophages and increasing the release of PGD2, which inhibits the hypertrophy of pulmonary vein smooth muscle cells (PVSMCs) and improves the remodeling of pulmonary vessels. This evidence concerns the gene PTGDS and pulmonary arterial hypertension.