RESUMO
Objective To observe the impact of mild hypothermia (MH)on the reactive oxygen species (ROS)and expression of cacpase-3mRNA and light chain 3 (LC3,a subunit of immunoglobulin)in hippocampus nerve cells of rats after cardiopulmonary resuscitation (CPR).Methods A total of 65 healthy male Sprague Dawley (SD)adult rats were randomly (random number)divided into 2 groups:blank control group (n =5)and CPR group (n =60).Cardiac arrest (CA)was induced in rats of CPR group by asphyxia.The survival rats after CPR were randomly (random number)divided into 2 groups:normothermia CPR group (NT)and hypothermia CPR group (HT).Homeothermia of 37 ℃ was maintained in NT group after restoration of spontaneous circulation (ROSC),and hypothermal intervention to 32 ℃ was carried out in HT group for 4 hours immediately after ROSC.Both NT group and HT group were then randomly divided to 2 subgroups 12 hours and 24 hours after ROSC (NT-12,NT-24,HT-12,HT-24 subgroups).During observation,the neurological deficit (NDS)of rats was scored,then the bilateral hippocampi were obtained from rats'head,and monoplast suspension of fresh hippocampus tissue was made immediately to determine the level of intracellular ROS by flow cytometry.Transmission electron microscope was used to observe the ultrastructure changes of cellular nucleus and mitochondria.Reverse transcription-polymerase chain reaction (RT-PCR)was used to determine the expression of caspase-3mRNA and Western-blotting (WB)was used to determine the level of LC3 in frozen hippocampus tissue.Measured data were analyzed with paired sample T test and One-Way ANOVA.Results Of 60 rats with CA,44 were successfully resuscitated (73%)and 33 survived until the end of the experiment (55%).The NDSs of rats in NT and HT groups were significantly reduced in comparison with BC group (F=8.107,P<0.05),while the NDSs of rats in HT-12 subgroup and HT-24 subgroup were significantly increased in comparison with NDSs of rats in NT-12 subgroup and NT-24 subgroup,respectively (t=9.692,P<0.01;t=14.374,P<0.01 ).The ROS in hippocampus nerve cells of rats in NT group and HT group were significantly increased compared to BC group (F=16.824,P<0.05 ),whereas the ROS in HT-12 and HT-24 subgroups were significantly reduced compared to ROS in NT-12 and NT-24 subgroups,respectively (t =9.836,P<0.01;t =7.499,P<0.01).The expressions of caspase-3 mRNA in hippocampus nerve cells of rats in NT and HT groups were significantly increased compared to BC group (F=24.527,P<0.05),while the expressions of caspase-3 mRNA in rats of HT-12 and HT-24 subgroups were significantly reduced compared to NT-12 and NT-24 subgroups,respectively (t =6.935,P <0.01;t =4.317,P <0.01 ).The level of LC3B-II/I in hippocampus nerve cells of rats in NT and HT groups were significantly increased compared to BC group (F=6.584,P<0.05),while the levels of LC3B-II/I in rats of HT-12 and HT-24 subgroups were significantly reduced compared to NT-12 and NT-24 subgroups,respectively (t=10.836,P<0.001;t=2.653,P=0.02).Ultrastructure damage of nucleus and mitochondria in NT group was more evident compared to BC group,and eumorphism of nucleus and mitochondria were maintained in rats of HT group compared to NT group.Conclusions The mild hypothermia reduced the injury of nerve cells and improved the neurological function of rats survived from cardiac arrest likely by reducing ROS production of nerve cells and inhibition the expression of caspase-3mRNA and lowering the level of LC3 leading to reducing cellular apoptosis and massive autophagy in rats survived from cardiac arrest after CPR.