Glycine minimizes reperfusion injury in a low-flow, reflow liver perfusion model in the rat

This study investigated the effects of glycine on reperfusion injury in a low-flow reflow liver perfusion model. With this protocol, livers were perfused at low flow rates of similar to 1 ml . g(-1) . min(-1) for 75 min, which caused cells in pericentral regions of the liver lobule to become anoxic because of insufficient delivery of oxygen. When normal flow rates (similar to 4 ml . g(-1) . min(-1)) were restored for 40 min, an oxygen-dependent reperfusion injury occurred. Upon reflow, lactate dehydrogenase (LDH), a cytosolic enzyme, and malondialdehyde (MDA), an end product of lipid peroxidation, were released into the effluent perfusate. LDH increased from basal levels of similar to 1-35 IU . g(-1) . h(-1) in livers from control rats. Glycine (0.06-2.00 mill) minimized enzyme release in a dose-dependent manner (half-maximal decrease = 133 mu M), with maximal values only reaching 5 IU . g(-1) . h(-1) when glycine was increased to 2 mM. Reflow for 40 min after 75 min of low-flow hypoxia caused death in similar to 30% of previously anoxic parenchymal cells in pericentral regions; however, infusion of glycine (2 mM) decreased cell death to less than 10%. Strychnine (1 mM), which was found to mimic the cytoprotective effect of glycine in proximal renal tubules, also reduced LDH release to 11 IU . g(-1) . h(-1) in this study. Bile was released at rates of similar to 42 mu l . g(-1) . h(-1) in livers from control rats, but values were not altered significantly by glycine. Maximal MDA production during reperfusion decreased by 35% with 0.6 mM of glycine. Trypan blue distribution time, an indicator of hepatic microcirculation, was reduced significantly by glycine at 5 and 40 min after reflow, but changes were about twofold greater at later time points compared with earlier ones (half-maximal decrease = 225 mu M). Time for oxygen to reach steady state upon reflow was reduced by glycine in a dose-dependent manner, and the rates of entry and exit of a dye confined to vascular space (fluorescein dextran) were increased two- to threefold by glycine, respectively. Taken together, these data indicate that a reperfusion injury that occurs in previously hypoxic pericentral regions of the liver upon reintroduction of oxygen is minimized by glycine, possibly by action on a glycine-sensitive anion channel to improve microcirculation during the reperfusion period.