PROTECTIVE EFFECT OF ISCHEMIC PRECONDITIONING ON LINER PRESERVATION-REPERFUSION INJURY IN RATS

Background, Ischemic-preconditioning is a process whereby a brief isch emic episode confers a state of protection against subsequent long-ter m ischemia-reperfusion injury. Ischemic preconditioning has been studi ed in heart and liver ischemia-reperfusion injury; however; few studie s have been performed in the model of preservation-reperfusion injury in liver transplantation. The current study was designed to evaluate t he ability of ischemic preconditioning to protect liver grafts from lo ng-term preservation-reperfusion injury. Methods. Male Sprague Dawley rats were used as donors and recipients of orthotopic liver transplant ation. Ischemic preconditioning was done by interruption of the portal vein and hepatic artery for 5, 10, and 20 min (5-10, 10-10, and 20-10 groups). Reflow was initiated by removal of the clamp for another 10 min in all groups. The liver was removed and placed in a bath with Eur o-Collins solution for different preservation times. Tolerance of the transplanted liver to cold ischemia was determined by survival time an d liver function tests. Rat tumor necrosis factor was analyzed by a bi oassay. No-Nitro-L-arginine methyl ester, L-arginine, or adenosine was administered to block or stimulate the synthesis of nitric oxide (NO) in the rats that received long-term-preserved liver grafts. Results. Twenty percent of syngeneic rats (n=10) that received a liver graft wi th a 16-hr cold ischemia time in Euro-Collins solution survived for mo re than 1 day and 10% survived for more than 5 days. In contrast, 87.5 % of rats (n=8) that received a liver graft with ischemic precondition ing (10-10 group) and 16 hr of cold ischemia survived for more than 1 day and 75% for more than 5 days. Recipients of liver grafts with isch emic preconditioning had significantly reduced levels of serum asparta te transaminase and tumor necrosis factor-alpha, as well as increased bile flow, compared with recipients of liver grafts without ischemic p reconditioning. Blockage of the NO pathway using N omega-nitro-L-argin ine methyl ester, a stereospecific competitive inhibitor of NO formati on, attenuated the protective effect of ischemic preconditioning, Admi nistration of one of two precursors of NO synthesis, L-arginine or ade nosine, prolonged the survival of rats that received 16-hr-preserved l iver grafts. In addition, L-arginine synergized with short-term ischem ic preconditioning (5-10 group) to increase the survival of rats that received a liver graft with a 16-hr cold ischemia time, and the surviv al rate was 83% after 5 days. Finally, prolonged ischemic precondition ing (greater than or equal to 20 min; 20-10 group) resulted in liver d amage and loss of function. Conclusion. The current results show that ischemic preconditioning protects the liver graft from subsequent long -term cold preservation-reperfusion injury in a rat liver transplantat ion model. The protective role of ischemic preconditioning may be medi ated by the endogenous production of NO.