This study examined the effect of inhaled nitric oxide (NO) on lung neutrophil accumulation and endothelial-dependent and -independent guanosine 3',5'-cyclic monophosphate (cGMP)-mediated mechanisms of pulmonary vasorelaxation after mesenteric ischemia-reperfusion (I/R) in mechanically ventilated rats. Inhaled NO (20 ppm) was administered in two protocols: 1) throughout mesenteric I/R and 2) during mesenteric reperfusion alone. Concentration-response curves were generated (10(-9) to 10(-8) M) for acetylcho-line (ACh), A23187, and sodium nitroprusside (SNP) in isolated pulmonary arterial rings preconstricted with phenylephrine. Lung neutrophil accumulation [myeloperoxidase assay (MPO)] was significantly increased from 2.4 +/- 0.2 units/g lung wt in controls to 10.3 +/- 0.4 after 1 h of superior mesenteric artery occlusion and 2 h of reperfusion. Lung MPO activity was not different from controls in rats receiving inhaled NO either 1) during mesenteric I/R or during mesenteric reperfusion alone. The concentration-response curves demonstrated significant impairment of pulmonary vasorelaxation by endothelial-dependent mechanisms (response to ACh and A23187) but not endothelial-independent pulmonary vasorelaxation (response to SNP) after mesenteric I/R. This pulmonary vasomotor dysfunction was prevented by administration of inhaled NO during either mesenteric I/R or during mesenteric reperfusion alone. We conclude that inhaled NO prevents lung neutrophil accumulation and pulmonary vascular endothelial dysfunction after mesenteric I/R.