Figure 1.

O₂⁻ contributes to pressure-dependent pulmonary arterial tone after chronic hypoxia (CH). Arterial tone (percentage of passive inner diameter) as a function of increasing intraluminal pressure in arteries from CH and control rats in the presence of (A) polyethylene glycol–superoxide dismutase (PEG-SOD; 120 U/ml), (B) polyethylene glycol–catalase (PEG-catalase; 250 U/ml), or their vehicle. Arteries were endothelium disrupted but not permeabilized to Ca²⁺. Vessel inner diameter was measured in 10-mm Hg pressure steps beginning at 5 mm Hg and ending at 45 mm Hg. Passive inner diameter was determined by repeating pressure steps after removal of extracellular Ca²⁺ (4). Values are mean ± SE of n = 4–5 rats/group. *P < 0.05 versus control. ^#P < 0.05 CH drug versus CH vehicle.