Protective Effect Of Pharmacological Preconditioning On Cerebral Ischemic Reperfusion Injury

The term "brain tolerance" describes as a phenomenon of transient resistance to a lethal insult evoked by preconditioning with a mild insult of short duration. Preconditioning stimulus,while inadequate to damage neurons,somehow increases their ability,and sometimes the ability of the whole organism as well,to survive subsequent lethal challenge.IP has been described to be a biphasic event:the acute phase is limited to 1-3 h after a brief ischemic stimulus,and the delayed phase emerges 24 h later and may last up to 72h.A series of recent studies have described another relevant phenomenon termed "chemical preconditioning".Abelmoschl Manihot is one of the plants that rich in flavones,such as quercetin,hyperin and rutin,Recent studies have shown that total flavones of Abelmoschl Manihot(TFA) have protective effects against cerebral ischemic injury in rabbit and rat.Also,pharmacological preconditioning of TFA(PPA) has been shown to possess a protective effect against myocardial ischemia-reperfusion injury in rabbit.However,there is no information reported about the effect of PPA on cerebral ischemic injury.By using rat,mice model of cerebral ischemia and the hypoxia-reoxygen model of foetal hippocamal neurons,we set out to investigate the effect of PPA on cerebral and its mechanism.1.Effects of PPA in the acute phase on the model of cerebral ischemic injury in ratIschemia and reperfusion(I/R) injury was induced by a middle cerebral artery occlusion(MCAO) for 90 minutes occlusion and 60 minutes of reperfusion in rat.PPA rats received 2 cycles of 5 minutes intravenous injection of TFA 20,40,80,160 mg·kg^-1 30 min before I/R.20,40,80,160 mg·kg^-1 PPA significantly reduced the infarction volume,markedly inhibited the elevated levels of serum LDH,MDA,PGE2 and decrement of serum NO and NOS.2.Effect of PPA of the middle phase on the model of cerebral ischemic injury in ratThe rat I/R injury was induced by MCAO for 90 minutes occlusion and 60 minutes of reperfusion.TFA(20,40,80,160 mg·kg^-1 )pretreatment 7 h has no significant effect on the infarction volume.3.Effect of PPA in the delayed phase on the model of cerebral ischemic injury in ratThe rat I/R injury was induced by MCAO for 90 minutes occlusion and 60 minutes of reperfusion.TFA or Nim pretreatment 36 h significantly decreased the infarction volume.PPA(20,40,80,160 mg·kg^-1) or Nim significantly inhibited the elevated levels of serum LDH and MDA,indicating a delayed protective effect of TFA preconditioning on cerebral ischemic reperfusion injury.In addition,the serum NO level and the cerebral iNOS mRNA were up-regulated.4.Effect of PPA in the acute phase on the model of cerebral ischemic injury in miceThe mouse I/R injury was induced by MCAO for 90 minutes occlusion and 60 minutes of reperfusion.PPA animals received 2 cycles of 5 minutes intravenous injection of TFA 25,50,100,200 mg·kg^-1 30 min before I/R.TFA or Nim pretreatment significantly decreased the infarction volume.Increases of serum LDH,NSE activity and MDA level were observed after I/R,but these changes were inhibited in mice pretreated with either TFA(25,50,100,200 mg·kg^-1) or Nim,In addition,the serum NO level were up-regulated.5.Effect of EDHF on hippocampal neurons subjected to oxygen deprivation/reperfusion in primary cultureTreatment with 1μmol·L^-1 Ach and a segment of cerebral artery significant increase the neuron viability(P＜0.01,compared with model),and reduce the activity of LDH in culture medium.Plus with the Indo and the L-NAME didn't influence the effect of Ach plus cerebral artery.6.Effect of TFA on hippocampal neurons subjected to oxygen deprivation/reperfusion in primary culture.Pretreatment with TFA(100 mg·kg(-1)) and cerebral artery significantly increase the neuron viability(P＜0.01,compared with model),reduce the activity of LDH in culture medium.TFA(3,10,30,100 mg·kg^-1) plus with cerebral artery lowered the calcium concentration in neuron(compared with model).Conclusion:PPA has marked protective effect on cerebral ischemia and reperfusion injury,the mechanisms of PPA might be related to attenuating oxygen free radicals, increasing of NO production,inhibiting the calcium concentration in neuron.