Hyperoxia/complications; Hypertension, Pulmonary/etiology; Lung/blood supply; Pulmonary Artery/physiopathology; Vasoconstriction; Animals; Animals, Newborn; Disease Models, Animal; Dose-Response Relationship, Drug; Enzyme Activation; Familial Primary Pulmonary Hypertension; Female; Free Radical Scavengers/pharmacology; Hydrogen Peroxide/metabolism; Hyperoxia/enzymology; Hyperoxia/physiopathology; Hypertension, Pulmonary/enzymology; Hypertension, Pulmonary/physiopathology; Lung/drug effects; Lung/metabolism; Male; Oxidative Stress; Peroxynitrous Acid/metabolism; Pulmonary Artery/drug effects; Rats; Rats, Sprague-Dawley; Sex Factors; Superoxide Dismutase/metabolism; Superoxides/metabolism; Time Factors; Up-Regulation; Vasoconstriction/drug effects; Vasoconstrictor Agents/pharmacology; rho-Associated Kinases/metabolism