Hypoxic constriction and reactive oxygen species in porcine distal pulmonary arteries

Divisions of Pulmonary and Critical Care Medicine and Cardiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224 Submitted 10 October 2002 ; accepted in final form 24 March 2003 To determine whether reactive oxygen species (ROS) play an essential role in hypoxic pulmonary vasoconstriction (HPV) and the cellular locus of ROS production and action during HPV, we measured internal diameter (ID) at constant transmural pressure, lucigenin-derived chemiluminescence (LDCL), and electron paramagnetic resonance (EPR) spin adduct spectra in small distal porcine pulmonary arteries, and dichlorofluorescein (DCF) fluorescence in myocytes isolated from these arteries. Hypoxia (4% O 2 ) decreased ID, increased DCF fluorescence, tended to increase LDCL, and in some preparations produced EPR spectra consistent with hydroxyl and alkyl radicals. Superoxide dismutase (SOD, 150 U/ml) or SOD + catalase (CAT, 200 U/ml) did not alter ID during normoxia but reduced or abolished the constriction induced by hypoxia. SOD also blocked HPV in endotheliumdenuded arteries after restoration of the response by exposure to 10 -10 M endothelin-1. Confocal fluorescence microscopy demonstrated that labeled SOD and CAT entered pulmonary arterial myocytes. SOD, SOD + CAT, and CAT blocked the increase in DCF fluorescence induced by hypoxia, but SOD + CAT and CAT also caused a stable increase in fluorescence during normoxia, suggesting that CAT diminished efflux of DCF from cells or oxidized the dye directly. We conclude that HPV required increased concentrations of ROS produced by and acting on pulmonary arterial smooth muscle rather than endothelium. vascular smooth muscle; endothelium; electron paramagnetic resonance; dichlorofluorescein; lucigenin; superoxide dismutase; catalase Address for reprint requests and other correspondence: J. T. Sylvester, Division of Pulmonary and Critical Care Medicine, The Johns Hopkins Asthma and Allergy Center, 5501 Hopkins Bayview Circle, Baltimore, MD 21224 (E-mail: jsylv{at}jhmi.edu ).