Role of reactive oxygen species in pulmonary hypertension. O2•−, superoxide anion; H2O2, hydrogen peroxide; PDE5, phosphodiesterase-5; GMP, guanosine monophosphate; cGMP, cyclic GMP; GTP, guanosine triphosphate; H2O, water; NO, nitric oxide; OONO•−, peroxynitrite; SOD, superoxide dismutase; BH4, tetrahydrobiopterin; BH2, dihydrobiopterin; NOS, nitric oxide synthase; eNOS, endothelial NOS; NADPH, nicotinamide adenine dinucleotide phosphate dehydrogenase. Reused, with permission, from Apitz C, et al., 2016 (25); Reused, with permission, from Dennis KE, et al., 2009 (148); Reused, with permission, from Fike CD, et al., 2008 (181); Reused, with permission, from Irodova NL, et al., 2002 (267); Reused, with permission, from Wedgwood S and Black SM, 2003 (620).