Melatonin attenuates posttransplant lung ischemia-reperfusion injury

Background. Melatonin, a pineal hormone, is a free radical scavenger and an antioxidant. The purpose of this study was to assess the protective effect of melatonin on posttransplant lung ischemia-reperfusion injury. Methods. Rat single-lung transplantation was performed in two (n = 10) experimental groups after 18 hours of cold (4°C) ischemia. Group I animals consisted of the ischemic control group. In group II, donor and recipient animals were treated with intraperitoneal injection of 10 mg/kg melatonin 10 minutes before harvest and reperfusion, respectively. After 2 hours of reperfusion, oxygenation, plasma, and bronchoalveolar lavage nitrite levels were measured. Lung tissue was assessed for thiobarbituric acid reactive substances and myeloperoxidase activity. Peak airway pressure was recorded throughout the reperfusion period. Results. The melatonin-treated group showed significantly better oxygenation (321.8 ± 33.8 mm Hg versus 86.1 ± 17.4 mm Hg; p < 0.001), reduced lipid peroxidation (0.65 ± 0.3 nmol/g versus 1.63 ± 0.8 nmol/g; p = 0.032), and reduced myeloperoxidase activity (0.56 ± 0.1 ΔOD · mg−1 · min−1 versus 1.01 ± 0.2 ΔOD · mg−1 · min−1; p = 0.032). Bronchoalveolar lavage nitrite levels in the transplanted lungs were significantly lower in group II than in group I (0.34 ± 0.06 μmol/L versus 1.65 ± 0.6 μmol/L; p = 0.016). In group II significant reduction in peak airway pressure was noted compared with group I (p = 0.002). Conclusions. In this model, exogenously administered melatonin effectively protected lungs from reperfusion injury after prolonged ischemia.