Changes of the activity of ERK1/2 signaling pathway in lung after total hepatic ischemia-reperfusion in rats and effects of melatonin

Objective To explore the dynamic changes of the activity of extracellular signal-regulated kinases 1/2(ERK1/2) signaling pathway and its significance in lung injury and repair after total hepatic ischemia –reperfusion(I/R) of rats,and melatonin's effects on this pathway.Methods This study was divided into 2 parts.In the first part,36 healthy male SD rats weighing 250-300 g were randomly divided into 6 groups(n=6):①pre-ischemia group,②reperfusion 0.5 h group,③reperfusion 3 h group,④reperfusion 6 h group,⑤reperfusion 12 h group,⑥reperfusion 24 h group.Total hepatic I/R was produced by occlusion of hepatic helium for 30 minutes,and the occlusion was then released for reperfusion.The animals were killed at 5 minutes prior to ischemia and 0.5 h,3 h,6 h,12 h,24 h of reperfusion,and the lung tissue was taken for determation of ERK1/2,pERK1/2 protein expression,apoptotic cells,PCNA protein expression and histological examination,to observe the dynamic changes of the activity of ERK1/2 signaling pathway and its relationship with cell proliferation and apoptosis.In the second part,12 healthy male SD rats weighing 250-300 g were randomly divided into 2 groups(n=6):melatonin group and vehicle group.Melatonin(0.5%,10 mg·kg-1)or vehicle of the same volume was injected via femoral vein 15 min before ischemia and 10 min before reperfusion,the animals were killed at 3 h of reperfusion,and the lung tissue was taken to determine the same parameters to observed the effects of melatonin.Results(1)Compared with that in pre-ischemia group,the p-ERK/ERK ratio and PCNA-positive index were both decreased at 0.5 h of reperfusion,and then were increased gradually in the lung.While the apoptotic index was increased at 0.5 h of reperfusion and became higher gradually,which reached the peak at 6 h of reperfusion,then decreased slowly after that.Histological examination revealed that the lung was injured at 0.5 h of reperfusion,then worsened gradually,which reached the peak at 3 h of reperfusion and took a turn for the better after that.(2) Correlate analysis revealed that p-ERK/ERK ratio showed a positive correlation with PCNA-positive index(r=0.85,P0.01)and a negative correlation with apoptotic index(r=-0.38,P0.05).(3)Compared with that in vehicle group,p-ERK/ERK ratio was higher,the apoptotic index was lower,and the histological changes was less severe in melatonin group,but PCNA-positive index showed no difference between 2 groups.Conclusion The ERK1/2 signaling pathway was initially inhibited,then was gradually activated with the injury and repair of lung after total hepatic I/R,and the pathway may play an active role in the self-repair of the injured lung through anti-apoptosis and promoting proliferation.Melatonin can activate ERK1/2 pathway,through which melatonin may alleviate hepatic I/R induced lung injury.