Inhaled nitric oxide pretreatment but not post-treatment attenuates ischemia-reperfusion-induced pulmonary microvascular leak

Background: Ischemia-reperfusion (VR) pulmonary edema probably reflects a leukocyte-dependent, oxidant-mediated mechanism Nitric oxide (NO) attenuates leukocyte-endothelial cell interactions and I/R-induced microvascular leak. Cyclic adenosine monophosphate (cAMP) agonists reverse and prevent I/R-induced microvascular leak, but reversal by inhaled NO (INO) has not been tested In addition, the role of soluble guanylyl cyclase (sGC) activation in the NO protection effect is unknown. Methods: Rat lungs perfused with salt solution were grouped as either I/R, I/R with INO (10 or 50 ppm) on reperfusion, or time control. Capillary filtration coefficients (Kfc) mere estimated 25 min before ischemia (baseline) and after 30 and 75 min of reperfusion. Perfusate cell counts and lung homoge nate myeloperoxidase activity mere determined in selected groups. Additional groups were treated with either INO (50 ppm) or isoproterenol (ISO - 10 mu M) after 30 min of reperfusion. Guanylyl cyclase mas inhibited with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ - 15 mu M), and Kfc was estimated at baseline and after 30 min of reperfusion. Results: (1) Inhaled NO attenuated VR-induced increases in Kfc. (2) Cell counts were similar at baseline. After 75 min of reperfusion, lung neutrophil retention (myeloperoxidase activity) and decreased perfusate neutrophil counts were similar in all groups. (3) In contrast to ISO, INO did not reverse microvascular leak. (4) 8-bromoguanosine 3',5'-cyclic monophosphate (8-br-cGMP) prevented I/R-induced microvascular leak in ODQ-treated lungs, but INO was no longer effective. Conclusions: Inhaled NO attenuates VR-induced pulmonary microvascular leak, which requires sGC activation and may involve a mechanism independent of inhibition of leukocyte-endothelial cell interactions. In addition, INO is ineffective in reversing VR-induced microvascular leak.