Features of Ductular Reaction in Rats with Extrahepatic Cholestasis.

Ductular reaction develops during liver regeneration, fibrosis, and carcinogenesis. However, the types, stages of formation, and topography of ductular profiles in various pathologies remain insufficiently studied. Using the model of common bile duct occlusion, we showed that the number and topography of ductular profiles are closely related to the duration of biliary obstruction. The ductular profiles can be located inside the portal tract, along the existing bile ducts, and/or intramurally, around the portal vein, periportally, inside the lobules, in the portocaval fibrous connections, in the adventitia of the hepatic veins, in the septs connecting the portal tracts, and also in the "portal plate" of the liver. The ductular profiles can be formed as a result of expansion of existing bile ducts, cholangiocyte proliferation, as well as transdifferentiation of hepatocytes and activation of mesenchymal stem cells.

STRUCTURAL CHANGES IN RATS' LIVER DURING THE FIRST 2 WEEKS FOLLOWING 2/3 PARTIAL HEPATECTOMY.

Aim of study - Investigation of changes in hepatocyte size and shape and architecture of the sinusoidal network in 2-week dynamics after resection 2/3 of the liver. The experiments were performed on 16 adult male Wistar rats weighing 190-200 grams who underwent 2/3 resection of liver, while a resected portion of the liver of the same rat was considered as a control. We examined liver tissue by histological, immunohistochemical, morphometrical methods, and the architecture of the sinusoidal capillary network by electron microscopy of corrosion casts. The study was conducted in 24 hours, 48 hours, 96 hours, 1 week, and 2 weeks after surgery. The shape and size of the hepatocytes in the first and third zones of the liver acinus change with the term of the experiment. With changes in the shape and size of hepatocytes, new intercellular connections are formed, including with the involvement of atypical membrane protrusions of deformed neighboring hepatocytes. One week after regeneration, electron microscopic examination of corrosion casts reveals a network of sinusoids that spatially define lobules of different shapes and sizes, including those that appear to be a combination of two "normal" lobules. Superficial sinusoids are often markedly dilated (up to 25 µm). In addition, small-diameter (6-7µm) sinusoidal casts with a rough surface and small bud-shaped protrusions are observed in some areas, giving the line of this a zigzag shape. The existence of hepatic vein tributaries and associated with them large sinusoids, found In single areas, reveals the characteristic feature of vascular sprouting. Based on the data obtained, it can be assumed that despite the recovery of liver mass, the regeneration process is not complete. Regenerated liver undergoes a permanent process of transformation of hepatocytes' shape and size, as well as the transformation of the vascular network, which is the basis for changes in the spatial architecture of the liver lobules.

Spatial Organization of the Transport of Interstitial Fluid and Lymph in Rat Liver (Scanning Electron Microscopy of Injection Replicas).

Using the method of scanning electron microscopy of injection replicas, we studied the movement of a new injection mass between the blood microcirculation system, interstitial space, lymphatic system, and bile transport system in rat liver under normal conditions and 3 days after the occlusion of the common bile duct. The casts of the perisinusoidal spaces of Disse's after injection of the injection mass through the portal vein and common bile duct were obtained. Their direct transition not only in "leakages" structurally related to lymphatic capillaries in interlobular spaces, but also in perivascular spaces around the portal and hepatic veins. The flow of the injection mass through the perivascular spaces leads to the formation of peculiar "sheaths" around hepatic veins and components of the portal complex. The proposed approach allows effective visualization of the structural basis of interaction of various compartments of the fluid microcirculation in the liver under normal and pathological conditions.

DUCTULAR REACTION AT THE EARLY AND LATE STAGES OF BILIARY OBSTRUCTION: IS THE MECHANISM THE SAME?

Ductular reaction (DR) is one of the classical features of biliary obstruction in humans as well as in experimental models. It is the histological phenomenon expressed by the increased number of ductular profiles (DPs), which is especially intensively studied in rodents' model of common bile duct ligation (CBDL). However, some issues related with DR in long-term CBDL are not clear enough. The liver tissue of male Wistar rats (150-200 g) subjected to CBDL were studied histologically (H&E). The architectonics of the biliary tract was studied by investigation of the corrosion casts obtained by retrograde injection (trough CBD) the solidified mass prepared on the basis of "Protacryl M" widely implemented in orthopedic dentistry. The casts were investigated by electro-optic device ProScope-HR with magnification X10, X50 and X200. DR accompanying CBDO is featured by the development of new DPs, the number of which is permanently increased in association with the prolongation of the terms of Cholestasis. DPs continue to develop in all areas of liver lobules - from portal/periportal region up to the regions containing central veins (hepatic veins tributaries of small calibers). The part of DPs has wide lumens, while the lumens of another part of DPs are hardly notable. In spite of evident ductular metaplasia of hepatic tissue, the small groups of normal by form and structure hepatocytes forming the separate small islets could be revealed. Histological features of these hepatocytes support the proposition that these cells maintain the functional activity on the 4th-5th weeks after CBDO. The results of investigations of biliary corrosion casts on the 4th and 5th weeks of CBDO show that solidifying mass cannot reach the small ducts/ductules and especially bile canaliculi. This fact confirms the interruption of ductular-canalicular junctions (IDCJ). We propose that due to IDCJ the increased pressure in preserved bile canaliculi should stipulate the mitotic activity and biliary trans-differentiation of hepatocytes on the late terms of CBDO and support the generation of ductal-like structures and appearance of new DPs. These ductules generally are not drained into the entire biliary tree.