Mitochondria Load Degree in Hepatocytes of the Classical Hepatic Lobules in Chinchilla (Chinchilla lanigera)

Hepatocytes represent the majority of the liver cell population and are arranged in the form of cords placed in intimate contact with the sinusoidal capillaries. The functional complexity corroborated with the intensity of the activity of hepatocytes requires large amounts of energy. The organelles involved in the production of chemical energy used in the activity of hepatocytes are the mitochondria. The purpose of this study was to verify the mitochondrial load of hepatocytes in all areas of the classical hepatic lobules, in order to indirectly assess the intensity of hepatocyte activity in each area. Materials and Methods Five fresh corpses of chinchilla (Chinchilla lanigera) from an independent breeder from Bistrița-Năsăud county were used. Liver fragments were harvested and fixated in Kolster’s solution for 24 hours, stained with Heidenhain ferric hematoxylin, and assessed using Olympus BX41 microscope. Fixation with Kolster's solution and the staining with Heidenhain's iron hematoxylin clearly shows the hepatocytic mitochondria in shades from gray to black. The liver lobules displayed an uneven distribution of mitochondria depending on the area. In zone 1 of the classical hepatic lobule, the degree of loading of hepatocytes with mitochondria is larger than in zone 2 and much larger than in zone 3. Morphological features of the hepatocytes, including the number and distribution of mitochondria in the hepatic lobules, should improve the understanding of the physiology and pathology of the liver.

The Potential of the FSP1cre-Pparb/d−/− Mouse Model for Studying Juvenile NAFLD

Non-alcoholic fatty liver disease (NAFLD) can progress from steatosis to non-alcoholic steatohepatitis (NASH) characterized by liver inflammation, possibly leading to cirrhosis and hepatocellular carcinoma (HCC). Mice with impaired macrophage activation, when fed a high-fat diet, develop severe NASH. Evidence is mounting that Kupffer cells are implicated. However, it is unknown whether the resident CD68+ or bone marrow-derived CD11b+ Kupffer cells are involved. Characterization of the FSP1cre-Pparb/d−/− mouse liver revealed that FSP1 is expressed in CD11b+ Kupffer cells. Although these cells only constitute a minute fraction of the liver cell population, Pparb/d deletion in these cells led to remarkable hepatic phenotypic changes. We report that a higher lipid content was present in postnatal day 2 (P2) FSP1cre-Pparb/d−/− livers, which diminished after weaning. Quantification of total lipids and triglycerides revealed that P2 and week 4 of age FSP1cre-Pparb/d−/− livers have higher levels of both. qPCR analysis also showed upregulation of genes involved in fatty acid β-oxidation, and fatty acid and triglyceride synthesis pathways. This result is further supported by western blot analysis of proteins in these pathways. Hence, we propose that FSP1cre-Pparb/d−/− mice, which accumulate lipids in their liver in early life, may represent a useful animal model to study juvenile NAFLD.

The activities of three enzymes of haem synthesis during hepatic erythropoiesis in the mouse embryo

Aminolaevulinate synthetase, aminolaevulinate dehydratase, and haem synthetase, three enzymes which may have a regulatory role in haem synthesis, have been determined in liver extracts from different foetal stages of the mouse. Haemoglobin synthesis increases rapidly from early on the 14th day, after fertilization, to reach a maximum late on the 15th day. Aminolaevulinate synthetase reaches a maximum on the 14th day, 24–36 h before the peak of haemoglobin synthesis, aminolaevulinate dehydratase on the 15th day, about 12 h before the peak of haemoglobin synthesis, and haem synthetase on the 17th day. Maximal activity of aminolaevulinate synthetase and aminolaevulinate dehydratase is of only a few hours' duration. Throughout embryonic development the activities of all three enzymes are higher than in the adult liver. The absence of a correlation of enzyme activity with foetal liver cell population changes implies that fluctuations in enzyme activity cannot be explained solely by changes in the proportions of different cell types. The high levels of activity relative to those of adult liver may be related to the high proportion of erythroid cells in the foetal liver. It is concluded that these enzymes are unlikely to form rate-limiting steps during the increase in haemoglobin synthesis between 14 and 15 days.

Stereologic Studies on Hypertrophied Liver Cells of Rats

Biphenylyl derivatives have been shown to be effective inhibitors of cholesterol biosynthesis. The administration of biphenylyl methylvaleric acid (BMVA), to rats reduces serum and liver cholesterol levels and at the same time induces liver enlargement. This hepatotrophic effect has been confirmed in recent studies, where it was demonstrated that this hepatomegaly was due to an absolute increase of the hepatic mass without changes in the liver cell population, as reflected by the diminished DNA concentration and unchanged total DNA content of the organ.Since this hepatocytic hypertrophy represents an ideal model for studying the process of drug-induced cell enlargement, the present study was aimed to determine the organelles responsible for the liver enlargement by combined light and electron microscopic stereology measurements. Groups of rats were fed 300 mg of BMVA per kg of body weight, mixed with the food.

COMBINED EFFECTS OF X-IRRADIATION AND 3′-METHYL-4-DIMETHYLAMINOAZOBENZENE ON LIVER CELL POPULATION

Livers of rats were exposed to 950 rads of X-irradiation. The liver cells were then induced to proliferate by the stimulus of partial hepatectomy. The regenerating livers consisted of two cell populations, one of colonies of ceils having normal amounts of DNA and the other having abnormal polyploid and aneuploid cells. Regeneration of the liver is attributed to the colonies with normal cells. When 3′-Me-DAB was fed to the X-irradiated animals, the behavior of these cell populations was reversed. The multiplication of abnormal cells was favored in the presence of the carcinogen. Changes in the percentage of mitotic irregularities, the mitotic rates, and the proportion of various stages of mitosis that resulted in the altered behavior of cell populations are discussed.

THE REPLICATION TIME AND PATTERN OF THE LIVER CELL IN THE GROWING RAT

Three-week-old male rats of the Wistar strain were given tritiated thymidine, 1 µc/gm body weight, intraperitoneally and were killed at intervals from 0.25 to 72 hours later. Autoradiographs were made from 5 µ sections, stained by the Feulgen method. The replication time and its component intervals were determined from the scoring of the labeling of interphase nuclei as well as of prophase, metaphase, anaphase, and telophase nuclei. Absorption of the intraperitoneally injected label is rapid and is attended by "flash" labeling during interphase. The results show that at any one time about 4 per cent of the liver cells are synthesizing DNA preliminary to cell division. These cells alternate with waves of other cells and it is estimated that about 10 per cent of the liver cell population is engaged in cell duplication. The replication time is about 21.5 hours, and its component intervals occupy the following times: DNA synthesis, 9 hours; post-DNA synthesis gap, 0.50 hour; prophase, 1.3 hours; metaphase, 1.0 hour; anaphase, 0.4 hour; telophase, 0.3 hour; postmitosis gap, 9.0 hours. A group of liver cells has been recorded in at least 3 successive replication cycles.