Because long-term pulmonary artery (PA) obstruction is associated with expansion of the systemic blood supply to the lung, chronic ischemia may not occur, and endothelium nitric oxide synthase (eNOS) function may be preserved in postobstructive pulmonary arteries. To test this hypothesis, we studied piglets 2 d or 5 wk after left PA ligation or a sham operation. We measured left lung ATP and lactate lung concentrations; calcium-dependent and calcium-independent NOS activities and eNOS protein; and left PA relaxations in response to acetylcholine, calcium ionophore, and sodium nitroprusside. Decreases in ATP and increases in lactate concentrations were significantly attenuated after 5 wk PA occlusion (p < 0.05 versus sham and 2-d ligation). Compared with sham and 2-d PA occlusion, calcium-dependent NOS activity and eNOS protein were lower in the long-term PA occlusion group. Calcium-independent NOS activity was unchanged. Acetylcholine and calcium ionophore relaxations were impaired after 5 wk, whereas only acetylcholine relaxation was impaired after 2-d PA occlusion. Relaxation to sodium nitroprusside remained unchanged. In conclusion, despite relative conservation of lung energy metabolism, prolonged PA occlusion decreased eNOS function and protein in postobstructive pulmonary arteries.