Action of phenobarbital on the ultastructure and the enzymatic activity of the mouse intestine and the mouse liver

Quantitative analysis of smooth endoplasmic reticulum proliferation in periportal, midzonal and perivenular hepatocytes of mice after administration of phenobarbital

Smooth endoplasmic reticulum (SER) proliferation after phenobarbital (PB) administration has been described to occur predominantly in perivenular hepatocytes. We analyzed by quantitative electron microscopy changes in ER amounts in periportal, midzonal and perivenular hepatocytes from mice injected with 35, 50, 100 or 150 mg/kg of PB once a day for 3 days. The SER proliferated in midzonal hepatocytes in addition to perivenular hepatocytes even when low doses (35 or 50 mg/kg) were administered, and in hepatocytes of all three zones in case of high doses (100 or 150 mg/kg). Moreover, net proliferation of SER after administration of an amount of PB was not different in hepatocytes of any zones where the proliferation occurred, except animals injected with 100 mg/kg. The results suggest that there is no difference in SER producing capacity in hepatocytes of three zones when the cells have recognized the stimulation of PB.

Quantitative analysis of smooth and rough endoplasmic reticulum proliferation in differentiating hepatocytes of midpostnatal mice treated with phenobarbital

The increase, expressed as a percentage of the control value, in the area of smooth endoplasmic reticulum (ER) per unit cytoplasmic volume did not differ between periportal and perivenular hepatocytes in 10-day-old mice injected with 50 mg/kg phenobarbital (PB) at 7, 8, and 9 days of age, whereas it was greater in perivenular than in periportal hepatocytes in 20-day-old animals injected with 100 mg/kg at 17, 18, and 19 days of age. Unexpectedly, the amount of rough ER increased after PB administration in both perivenular and periportal hepatocytes in the two age groups. Experiments done to determine the significance of the rough ER proliferation brought the following results. The intensity of immunohistochemical fluorescence for albumin decreased in both periportal and perivenular hepatocytes from 20-day-old animals treated with PB. NADPH-cytochrome c reductase activity increased in both smooth and rough microsomes in 20-day-old animals treated with PB. These results show that the predominant proliferation of smooth ER in perivenular hepatocytes after PB administration, characteristic of adult liver, arises between 10 and 20 days of age, and that rough ER proliferation, which is related to the increase in drug metabolism, is characteristic of the liver of midpostnatal mice.

The heterogeneity of hepatocytes during the postnatal development of the mouse

Development of the hepatocyte heterogeneity was studied histochemically during the postnatal period. At birth ornithine carbamoyltransferase (OCT). succinate dehydrogenase (SDH) and NADH dehydrogenase (NADHDH) activities were evenly distributed throughout the liver acinus. Slightly uneven distribution within the acinus appeared at 3 days after birth in SDH and at 4 days after birth in OCT and NADHDH, changing to that of adult type at 10 or 12 days after birth which is characterized by a marked difference in the activities between zone 1 and 3. However, in animals of all age groups studied, glycogen was decreased mainly in zone 1 and 2 after 6 or 10 h of fasting and glucose 6-phosphatase activity was markedly reduced or disappeared in zone 3 and often in zone 2 after carbon tetrachloride administration. The results show that so-called "functional and structural heterogeneity among hepatocytes" consists of at least two different components, that formed gradually during the postnatal development and that existing already at birth.

Ultrastructural localization of intestinal glucose-6-phosphatase activity during the postnatal development of the mouse

The development of the endoplasmic reticulum (ER) and the ultrastructural localization of glucose-6-phosphatase activity have been studied in the proximal jejunum and distal ileum during the postnatal period. One day after birth, the amount and the repartition of ER in the jejunal enterocytes are similar to that observed in postweaning period. In the following days an extensive proliferation of SER is noted in the supranuclear zone of the absorbing cells. From day 7 till postweaning period a gradual decrease of the amount of SER is observed and after weaning, the ultrastructure of the enterocytes is similar to that in the adult mouse enterocytes. At all time, a positive reaction for G-6-Pase activity is observed in the cisternae of the endoplasmic reticulum and in the nuclear envelope. In the distal ileum, the SER is poorly developed one day after birth. During the first two weeks, the ER increases but no extensive proliferation of SER can be noted as in the jejunum. The G-6-Pase activity can be visualized in the rough and smooth endoplasmic reticulum as well as in the nuclear envelope. It appears that the proliferation of SER could be interpreted as the morphologic expression of an increased G-6-Pase activity.

Distribution of glucose-6-phosphatase and 5-nucleotidase in the digestive system of two teleost fishes

The distribution and histochemical localization of G6Pase and 5-nucleotidase in the different parts of the alimentary canal of two teleost fishes, Heteropneustes fossilis and Barbus sophore have been studied. The major sites of activity of the two enzymes are intestinal mucosa and liver. G6Pase is localized in the cytoplasm of the absorptive cells of the intestinal mucosa while 5-nucleotidase is present in the cytoplasm as well as nucleus and cell membrane. In the intestine, the anterior portion shows more stronger activity than in the middle and posterior portions. Mild activity is also noticed in the mucosa and gastric glands of the stomach. G6Pase activity is stronger than 5-nucleotidase activity in all the portions. Weak 5-nucleotidase activity is found in the submucosal connective tissue and the nuclei of the intestine. The goblet cells, muscularis abd serosa are negative in all the portions. G6Pase activity is stronger in the herbivorous fish Barbus sophore than in the omnivorous form Heteropneustes fossilis. In the liver, stronger activity of two enzymes is localized in the hepatocytes surrounding the sinusoids. Connective tissue and endothelial lining are negative.