Long-standing ischemic tolerance induced by hyperbaric oxygen preconditioning in spinal cord of rabbits

AIM:To determine whether the ischemic tolerance induced by hyperbaric oxygen preconditioning in spinal cord of rabbits is long-standing.METHODS:In the first experiment,sixteen male New Zealand rabbits were randomly assigned to 2 groups(8 in each group).The animals in control group received room air and normal ambient pressure(1 h/d,5 d) while the animals in hyperbaric oxygen(HBO) group received HBO pretreatment(1000 mL/L O2,2.5 atmosphere absolute[ATA],1 h/d,5 d).At 24 h after the last treatment,the spinal cord ischemia was induced for 20 min by infrarenal aortic cross clamping.At day 1 and 2,7,14 and 21 after reperfusion,the neurologic function was scored by the Tarlov criteria(in which 4 was normal and 0 was paraplegia).In the second experiment,32 animals were randomly assigned to HBO group and control(16 in each group).The animals underwent the same treatment as described for the first experiment.Eight animals in each group were sacrificed respectively at day 2 and 21 after reperfusion and the spinal cords(L5-7) were removed immediately for histopathologic examination.The neurologic functions were scored before the rats were sacrificed.RESULTS:The neurologic function scores in HBO group were significantly higher than those in control group at all time points(P0.05),with no statistical differences between the scores at day 2 and those at day 7,14 or 21 in HBO group.The numbers of normal neurons in the anterior spinal cord in HBO groups were also significantly greater than those in control groups at day 2 and 21,with no statistical differences between day 2 and 21 in HBO groups.A strong correlation was found between the neurologic function scores and the numbers of normal neurons in anterior horn of spinal cord(r2 d=0.903,P0.01;r21 d=0.922,P0.01).CONCLUSION:Hyperbaric oxygen preconditioning induces ischemic tolerance in spinal cord of rabbits and the effect is long-standing.