Observation And Intervention Of Liver Injury Induced By Portal Hypertension Following Extensive Hepatectomy In Rats

BACKGROUND/AIMS: Primary and secondary liver cancer is the most frequently developed tumor that seriously threatens human health. At present, liver resection is still to remain the preferred and potent approach for treatment of liver tumors. The surgical mortality rate has been minimized as a result of improved patient selection and safer technique. Extended hepatectomy has an increasing tendency resulting from broadened indication and the extent of hepatectomy. Liver failure is the main cause of higher mortality, directly related to the rate of remaining functional liver.In the past, it is suggested that insufficient number of remained liver cells is the cause of postoperative liver failure. At present, it is emphasized that various harmful factors developed in the early stage decreased the number of viableliver cell furtherly, not enough to maintain normal liver function, and liver failure developed finally. Many factors are responsible for liver failure after hepatectomy, except for excessive inflammatory reaction, activation of Kupffer cells, and bacterial translocation. Portal hypertension may be the predominant mechanism of liver failure.The phenomenon of portal hypertention after liver resection is firstly observed in rat hepatectomy. It is also observed in human liver resection. After extensive hepatectomy the entire stream of portal blood is directly through the relatively small remnant, owing to decreasing area of sinusoidal vascular bed, one may predict the postoperative acute portal hypertension. Increase of portal pressure following resection of more than 30% of the liver, regardless of the presence or absence of cirrhosis, has been reported, and like the liver remnant after extensive hepatic resection, small-for-size grafts are exposed to excessive portal flow. Since the maximum additional hepatic blood flow volume that the liver can tolerate is 20%, very significant increase of the blood flow in the small-for-size graft and the remnant liver is obviously harmful to the liver cells. Liver injury resulting from excessive portal pressure can be potently proofed by firstly impaired liver cells around periportal zone. According to previous studies using a 90% hepatectomy model, almostly all rats would die in 24-48 hours postoperatively. Individual study using portalcaval shunt showed that portal pressure could be reduced to the normal level and prolonged survival time was acquired. But impaired liver regeneration was observed due to excess decompressure. It remains no succeeful reports about approaches that using SAL or medication to reduce partly the portal pressure following extensive liver resection. These methods may be promote liver regeneration. Therefore, it is essential to study injured effects induced from portal hypertension in postoperative early stage so that treating as early as possible to protect the amount of valid liver cells and to promise patients live through safely the stage of liver blood flow disturbance.In conclusion, this study is to measure the alterations of portal pressure and liver injuries after extensive liver resection, to investigate histological changes resulting from portal hypertension, to evaluate the protective effects of hepatic function and liver regeneration by depressing moderatedly the excessive portal pressure by means of splenic artery ligation and medication.METHODS: Male Sprague-Dawley rats weighing 300 to 325 gm were used. According to Higgins and Anderson's means, modified hepatectomy was performed under intraperitoneal injection 3% pentobarbital sodium. In Part One, rats were used to study the relationship between portal vein hemodynamic changes and liver failure and survival following varied percentage partial hepatectomy (70%, 85%, or 90%partial hepatectomy); rats were used to observe liver injuries induced by portal hypertension after 85%partial hepatectomy in Part Two; rats were used to intestigate whether varied decompression of portal pressure can protect liver function and have any influence on liver regeneration in Part Three. The rats in the last two parts were divided into four groups: simple partial hepatectomy group, splenic artery ligation, octreotide group, and prazosin group. Five rats in each group were killed for measurement of portal pressure, blood and liver collections from 5 minutes to day 7 after hepatectomy. Portal pressure was measured by a water manometer after a 22-G trocar had been inserted directly into the portal vein. Zero pressure was based on axillary line, and changes were measured in centimeters of saline. Splenic artery was doubly ligated by 1# silk suture at hilum of spleen. Prazosin, which concentration was 60μg/ml, was injected into left portal vein. The dose of santostatin was 2μg/0.1ml NS, and hypodermic injection was performed. Two milliliter syringe connected with scalp acupuncture was inserted into inferior caval vein to draw 1.5 ml blood. Liver biochemical indicator included ALT, AST and TBIL were measured by automatic biochemistry meter. According to the measured portal pressure, livers were fixed by portal vein perfusion under haemodynamic conditions identical to those existing in vivo. Forty rats were used to observe survival after hepatectomy. Liver microcirculation, hepatocye vacuolation, hepatonecrosis, and mitotic index were measured by HE stained sections. Injury of hepatocyte vacuolation and sinusoid endothelial cell was observed. All data were expressed in means±SD. The statistical comparison of multi-sample was carried out according to Kruskal-wallis H test; bis-sample according to Wilcoxon Signed Ranks test. The survival was estimated with Kaplan-Meier curves and the difference in survival between the groups was assessed using the log-rank test. SPSS 10.0 software serviced all statistical analysis and plotting.RESULTS: Hepatic injury induced by a sharply increased portal pressure, as demonstrated by increased serum levels of TBIL, ALT, and AST, was observed. A significantly higher, more prolonged blood release of biochemical indicator was observed after 85% hepatectomy than treatment groups. Portal pressure expressed ascensus tendency accompanied with augmentation of hepatectomized proportion after 70%, 85%, and 90% hepatectomy, survival was 100%, 20%, zero, respectively. All 85% extensive hepatectomized rats developed acute liver failure in early stage of postoperation. We found that the death time occurred within three days in almost all died rats (19/20). The rats surviving exceed three days almost not die (1/20). There was a relationship between the time characteristic and changes of serum biochemical indicators. The peak value of serum biochemical indicators appeared at 24 to 48 hours after hepatectomy, soon after fell off. The mortality also decreased meanwhile. It suggested that lethal liver failure mostly developed at early stage. It reminded us of decompression of portal pressure as early as possible could reduce the mortality. There was significant difference in 7-days survival between prazosin group and partial hepatectomized group. Sinusoid dilation, small vacuolus in hepatocyte were observed in HE stain section soon after postoperation 6 hours. Along with the time prolonging, the vacuolus greatened and fused, the punctiform necrosis developed at postoperation 24 hours. The histological changes became predominant at 48 hours. Significant sinusoid dilation, big vacuolus, cytoplasm rarefaction, hepatocyte swelling, schistic necrosis, and rare mitotic figure were observed. In TEM sections, because of injured sinusoid endothelial cell, liver cell exposed directly to excessive portal pressure, membrane invagination was the source of vacuolation. These pathological changes damaged the liver cell function accompanied with abnormal hepatic biochemical indicators. Significant decreased portal pressure, improved liver function, increased survival, and positive effect on liver regeneration were observed in group PRA. Santostatin reduced the portal pressure, mitigated the liver injury, but had a positive effect on liver regeneration. Lower remnant liver weight was measured in santostatin group compared with other treatment group. In pure partial hepatectomy group, there were not only serious liver injuries, but also significant depressed liver regeneration. Mitotic figures were not measured on 24 and rare on 48 hours sections, and only few mitotic figures could be found on 72 hours sections. In treatment group, the measurement moderately decreased the portal pressure not only mitigated degree of injuries but also promoted the trigger of liver regeneration. Gradually increased mitotic figures were observed following 24 hours. There was significant difference between treatment group and pure partial hepatectomy group. CONCLUSIONS: Our experimental data confirm that inhibition of liver regeneration and liver injury against liver cell and sinusoid endothelial cell can be induced by portal hypertension after extensive hepatectomy. We demonstrate firstly that moderate decompression not only mitigate liver injury, but also antelocate the priming of liver regeneration to regain valid liver cell population as early as possible to refrain from lethal liver failure.