| Hepatic ischemia/reperfusion injury is a common problem encountered in many clinical conditions . It affects directly on the outcome of the patients. Although many studies have been done in this field, it still remains an unsolved problem.More and more evidence indicate that preconditioning, such as ischemia and heat shock, could protect liver against I/R injuries. But these methods are less likely to be applied in clinical practice because of their extensive damages to the body. So it is necessary to find out a new way of preconditioning on the liver.It has been shown that heat shock protein 70s induced in several tissues and organs by low dose of ethanol exposure can protect several different kinds of cells from injuries. In addition, ethanol preconditioning(EPC) is more convenient and acceptable for clinical uses. It is thought to elicit several preconditioning-like protection of the liver.Based on these investigations, it has been confirmed that ethanol preconditioning is a safe and effective protocol for protection of the liver against I/R injuries in our prview studies. It has been found that the most optional ethanol preconditioning protocol is 40%/5g/Kg/24h prior to ischemia and the rats pretreated by this protocal can tolerance 90-minute ischemia. However, the tolerance time limite under these conditions and the mechanism of EPC remains unclear.Objective To investigate the tolerance limit and the protective effects and the related mechanism of rats to hepatic inflow occlusion by ethanol gavage prconditioning.Methods and ResultsPart â… To establish the maximum tolerance limit of rats to hepatic inflow occlusionHepatic inflow occlusion under portal vein blood bypass mode was adopted in this study.Rats were exposed to 40% ethanol at a dose of 5g/Kg body weight 24h prior to ischemia. Adult male and female Wistar rats were randomly divided into 2 groups: ischemia-reperfusion group (IR) and ethanol preconditioning group(EPC). The animalsurvival rate was calculated following 2 weeks of reperfusion after hepatic inflow occlusion of 120min. If no rat died of rats, the time of hepatic ischemia was extended until death occured. Results (l)The survival rate in rats was 100 percent in EPC group and 70 percent in IR group. There was significant difference between two groups(/?<0.05).(2)The survival rate decreased in rats undergoing hepatic inflow occlusion of 130min. The survival rate in rats was 80 percent in EPC group and 60 percent in IR group. Thus the initial safe tolerance limit of rats with ethanol gavage preconditioning to hepatic inflow occlusion was 120 minutes.Part II To investigate the protective effects of the ethanol preconditioning against 120min ischemia/reperfusion liver injuries.Adult male and female Wistar rats were randomly divided into six groups: the normal control group(N),ethanol group (E), ischemia/reperfusion group(IR),0.9%NS preconditioning combined with IR group(NPC),ethanol preconditioning combined with IR group(EPC)and ischemia preconditioning combined with IR group(IPC).The mortality of the rats was observed and serum ALT,AST activity, pathological changes of the liver, apoptic hepatocytes and liver ATP content were measured . Results showed that (l)The rats in EPC group recovered completely 24h after reperfusion, while those in NPCJPC and IR group did not recovery until 36h. The survival rates of rats in EPC group was significantly higher than that in IPC,IR and NPC group(ï¿¡><0.05). (2)Activity of ALT was increased much less in EPC group than in IR and NPC group(/?<0.05). (3)Activity of AST were not significantly different in EPC group to IR, NPC and IPC group(p>0.05). (4)Content of liver ATP in EPC group was lower than that in N group at 0, 3, 6, 12h after reperfusion, but was higher than that in NPC, IPC and IR group. (5) Pathological findings showed less injury in EPC group ,but severe and irreversible injuries of the liver in IR and NPC group were found at 24h after reperfusion. (6) The number of apoptotic hepatocytes in EPC group was lower than that in IPC, NPC and IR group after reperfusion.Part III Expression of HO-1 in rat liver pretreated by ethanol after ischemia-reperfusion injury.To explore the mechanism of protective effect of ethanol preconditioning against I/R liver injuries, expression of the HO-1 protein was detected by means of immunochemistry staining. Results showed that(l)In normal rat livers, HO-1 was weakly expressed only inKupffer cells. It should be noted that hepatocytes also showed distinct HO-1 expression, especially in cytoplasm with stronger positive staining around centrolobular veins.(2)Expression of HO-1 was induced in E group and reached peak value at 24h after ethanol gastric gavage.(3)In EPC group expression of HO-1 in the liver was only slightly increased at the end of the 120 min ischemia, while it was enhanced 3h after reperfusion and reached its peak level after 12h reperfusion . Expression of HO-1 was statistically higher in EPC group than in that 1R, IPC, NPC and E group 0x0.05). Conclusions1. Ethanol gavage preconditioning is a safe and effective protocol for liver pretreatment and the 120 minutes is the tolerance limit of rats to hepatic inflow occlusion by ethanol gavage preconditioning.2. Ethanol gavage preconditioning can effectively pretect the rat liver against I/R injuries caused by 120min ischemia.3. The expression of HO-1 be induced by ethanol gavage prconditioning, which maybe be one of the potent molecular mechanism of liver protection evoked by ethanol gavage preconditioning.
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