IntroductionNitric 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 uM for freshly explanted hearts to 0.7±0.2 and 0.2±0.08 gM 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. (Sigma Chemical Co.). Components were combined within 4 h of donor cardiectomy, and preservation solutions were kept at 4°C. All of these solutions were at the pH of LR (6.6). University of Wisconsin solution (UW) was purchased from Du Pont Co. Blood flow was restored to the graft exactly 1 h after removal from the cold preservation solution, and pulsation of the donor aortic stump was observed to assure patency of the anastomosis. 10 min after removal of the crossclamp, an electrocardiogram (ECG) was taken (polygraph from Grass Instrument Co., Quincy, MA), and the heart was judged by the same 1. Abbreviations used in this paper: 8-Br-cGMP, 8-bromoguanosine 3',5' monophosphate; EC, endothelial cell; HUVEC, human umbilical vein endothelial cell; L-arg, L-arginine; L-NMMA, NG-monomethyl-Larginine; LR, lactated Ringer's solution; NO, nitric oxide; NOS, nitric oxide synthase; NTG, nitroglycerin; UW, University of Wisconsin solution.Nitric Oxide Pathway and Cardiac Preservation for Transplantation 2291 Abstract blinded investigators throughout based on the presence...
