Liver structural transformation after partial hepatectomy and repeated partial hepatectomy in rats: A renewed view on liver regeneration

BACKGROUND The phenomenon of liver regeneration after partial hepatectomy(PH)is still a subject of considerable interest due to the increasing frequency of half liver transplantation on the one hand,and on the other hand,new surgical approaches which allow removal of massive space-occupying hepatic tumors,which earlier was considered as inoperable.Interestingly,the mechanisms of liver regeneration are extensively studied after PH but less attention is paid to the architectonics of the regenerated organ.Because of this,the question“How does the structure of regenerated liver differ from normal,regular liver?”has not been fully answered yet.Furthermore,almost without any attention is left the liver's structural transformation after repeated hepatectomy(of the re-regenereted liver).ATM To compare the architectonics of the lobules and circulatory bed of normal,regenerated and re-regenerated livers.METHODS The livers of 40 adult,male,albino Wistar rats were studied.14 rats were subjected to PH-the 1st study group(SG1);10 rats underwent repeated PH–the 2nd study group(SG2);16 rats were subjected to sham operation-control group(CG);The livers were studied after 9 months from PH,and after 6 months from repeated PH.Cytological(Schiff reaction for the determination of DNA concentration),histological(H&E,Masson trichrome,CK8 Immunohistochemical marker,transparent slides after Indian Ink injection,),morphometrical(hepatocytes areas,perimeters and ploidy)and Electron Microscopical(Scanning Electron Microscopy of corrosion casts)methods were used.RESULTS In the SG1 and SG2,the area of hepatocytes and their perimeter are increased compared to the CG(P<0.05).However,the areas and perimeters of the hepatocytes of the SG1 and SG2 groups reveal a lesser difference.In regenerated(SG1)and re-regenerated(SG2)livers,the hepatocytes form the remodeled lobules,which size(300-1200μm)exceeds the sizes of the lobules from CG(300-600μm).The remodeled lobules(especially the“mega-lobules”with the sizes 1000-1200μm)contain the transformed meshworks of the sinusoids,the part of which is dilated asymmetrically.This meshwork might have originated from the several portal venules(interlobular and/or inlet).The boundaries between the adjacent lobules(including mega-lobules)are widened and filled by connective tissue fibers,which gives the liver parenchyma a nodular look.In SG2 the unevenness of sinusoid diameters,as well as the boundaries between the lobules(including the mega-lobules)are more vividly expressed in comparison with SG1.The liver tissue of both SG1 and SG2 is featured by the slightly expressed ductular reaction.CONCLUSION Regenerated and re-regenerated livers in comparison with normal liver contain hypertrophied hepatocytes with increased ploidy which together with transformed sinusoidal and biliary meshworks form the remodeled lobulli.