Apoptosis following ischemia-reperfusion injury in a rabbit lung ex-vivo model

Background. Apoptosis is postulated as a mechanism involved in lung ischemia-reperfusion (IR) injury, however, the relative contributions of ischemia and reperfusion are unclear.Methods. Heart-lung blocks were harvested from New Zealand white rabbits (3.0--4.0 kg) and exposed to 0, 6, or 18 hours of cold ischemia (4°C), followed by 3 hours of reperfusion in an ex vivo model. Terminal dUTP nick-end labeling (TUNEL), the technique used most often for detection of apoptosis, was performed on the tissue sections.Results. TUNEL demonstrated minimal apoptosis in lungs exposed to 0, 6, or 18 hours of ischemia with insignificant differences (p = 0.6 for 0 h vs. 18 h). After one hour of reperfusion, the level of TUNEL in the 18 hour ischemic tissue was significantly increased (p < 0.05 for 0 h vs. 18 h). During the period of reperfusion, the extent of apoptosis increased in direct proportion to the duration of ischemia; the level of TUNEL staining after 2 hours of reperfusion was significantly greater in the 18 hour ischemic tissue compared to the 6 hour ischemic tissue (p < 0.05), as was the 6 hour compared to the 0 hour (p < 0.01). The hallmark of apoptosis, nucleosomal ladders of 180--200 base pair DNA fragments, corresponded in intensity on gel electrophoresis to the quantitation of TUNEL. The characteristics of apoptotic cells including cell membrane blebbing, chromatin condensation and fragmentation were confirmed by electron microscopy.Conclusions. These results provide evidence that apoptosis may be a specific feature of IR injury in pulmonary tissue