HPGDS and pulmonary arterial hypertension: 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.