Nitric oxide (NO) is a novel
biologic messenger with diverse effects but its role in
organ transplantation remains poorly understood. Using a porphyrinic microsensor, the first direct measurements of coronary vascular and endocardial NO production were made. NO was measured directly in the effluent of preserved, heterotopically transplanted rat hearts stimulated with
L-arginine and
bradykinin; NO concentrations fell from 2.1 +/- 0.4 microM for freshly explanted hearts to 0.7 +/- 0.2 and 0.2 +/- 0.08 microM for hearts preserved for 19 and 38 h, respectively. NO levels were increased by SOD, suggesting a role for
superoxide-mediated destruction of NO. Consistent with these data, addition of the NO donor
nitroglycerin (NTG) to a balanced
salt preservation
solution enhanced graft survival in a time- and dose-dependent manner, with 92% of hearts supplemented with NTG surviving 12 h of preservation versus only 17% in its absence. NTG similarly enhanced preservation of hearts stored in University of Wisconsin
solution, the clinical standard for preservation. Other stimulators of the NO pathway, including
nitroprusside,
L-arginine, or
8-bromoguanosine 3',5' monophosphate, also enhanced graft survival, whereas the competitive
NO synthase antagonist
NG-monomethyl-L-arginine was associated with poor preservation. Likely mechanisms whereby supplementation of the NO pathway enhanced preservation included increased blood flow to the reperfused graft and decreased graft
leukostasis. NO was also measured in endothelial cells subjected to
hypoxia/reoxygenation and detected based on its ability to inhibit
thrombin-mediated platelet aggregation and
serotonin release. NO became undetectable in endothelial cells exposed to
hypoxia followed by reoxygenation and was restored to normoxic levels on addition of SOD. These studies suggest that the NO pathway fails during preservation/
transplantation because of formation of
oxygen free radicals during reperfusion, which quench available NO. Augmentation of NO/cGMP-dependent mechanisms enhances vascular function after
ischemia and reperfusion and provides a new strategy for
transplantation of vascular organs.