Bile acid metabolism in partially hepatectomized rats

The bile flow and the bile acid secretion, calculated on liver weight basis, increased 12 H and 24 H after 60-70% hepatectomy and returned to the initial levels thereafter. The biliary phospholipid secretion much more increased than bile acids, but the cholesterol secretion decreased. Bile acid composition changed with an increase of the cholic acid group and a decrease of the chenodeoxycholic acid group in both bile and feces. These changes almost disappeared on Day 14. The pool size of bile acid decreased maximally on Day 4 to about 40% of the initial, but the distribution of bile acids in the enterohepatic circulation was not changed. The fecal cholesterol and coprostanol markedly decreased on Day 2 but gradually returned to the initial levels according to the recovery of diet intake. The fecal bile acids decreased on Day 2, increased on Day 4, and returned to the normal range after Day 7. In conclusion, the regenerating liver secretes more bile, bile acids and phospholipids, and less cholesterol than the normal liver. Cholic acid predominates in the bile acids. These changes restored to the initial levels by about one week after the operation.     

Cellular ultrastructure of the hepatic sinusoid in partially hepatectomized rats

In male Wistar rats weighing 160-200 g 2/3 of the liver tissue was removed. As a result the phase modifications of lysosome structures in Kupffer's cells have been observed. 2.5 hours after operation the number of primary lysosomal granules increased, 9 hours later an augmentation in size and polymorphism of lysosomes was revealed. At the moment of hepatocyte mitotic peak, i. e. 30 hours after partial liver removal mainly secondary lysosomes were detected in Kupffer's cells. On the contrary, 48 hours following operation the number of new wave of accumulation of primary lysosomal granules was seen. In endothelial cells the lipid infiltration was prevalent especially at the hepatocyte mitotic peak period. The data obtained indicate specific relationship of ultrastructural modifications in sinusoidal cells and phases of the liver reparative regeneration.     

Oxidative stress in primary culture hepatocytes isolated from partially hepatectomized rats

The aim of this study was to evaluate the influence of partial hepatectomy prior to cell isolation on hepatocytes in vitro. We characterized the possible changes of various stress oxidative parameters within the first 24 h after seeding. Male Wistar rats served as donors. Hepatocytes were isolated by collagenase digestion from either liver of simulated surgery (SH) or from liver 1 h after 70% hepatectomy (PH), and the changes in stress parameters were analyzed after 1, 3, 18, and 24 h in culture. At 24 h, only hepatocytes from PH maintained significantly increased reactive oxygen species production, oxidized glutathione percentage, and Cu/Zn superoxide dismutase and catalase activities. Our results show that hepatocytes suffer significant cell injury as a result of the isolation procedure, but primary cultured cells from SH metabolically recover from this stress after 18 h. After this time, primary culture hepatocytes primed by PH maintain their in vivo-like metabolic activities (increase in both oxidative stress and antioxidant status).     

Serum ethanolamine and hepatocyte proliferation in perinatal and partially hepatectomized rats

It has been shown that the administration of ethanolamine (Etn) to partially hepatectomized rats enhances stimulation of DNA synthesis in regenerating hepatocytes. The present study aimed to test the hypothesis that the level of serum Etn in vivo may be regulated to control the growth of hepatocytes. Concentrations of serum Etn were determined in rats 1) of varying ages (from embryonic-19 (E-19) to 7-week-old), and 2) during regeneration following two-thirds hepatectomy (PH), to investigate whether serum Etn concentration correlates with the rate of proliferation of hepatocytes in growing animals or during regeneration. Serum Etn levels were 3 fold higher in E-19 fetuses and newborns than in adults, and were increased 2 fold 4 h after PH and remained high for at least 24 h. Results in both systems indicated a significant positive correlation between the rate of hepatocyte proliferation and serum Etn levels. Furthermore, Etn supplementation of 0.1 to 1 mmol immediately after PH promoted a significant weight gain and stimulated phosphatidylethanolamine (PE) and phosphatidylcholine (PC) synthesis in the regenerating liver. We also observed that whenever serum Etn levels were elevated, the metabolism of PE and PC in the liver changed dynamically, first by elevating the net synthesis of PE. Taken together, these results suggested that the levels of serum Etn might be regulated based on the physiological state of an animal, which consequently regulates the proliferation of hepatocytes.     

Toxic effects of 2-methyl-4-dimethylaminoazobenzene in normal and partially hepatectomized rats

In order to obtain a more precise definition of the conditions under which 2-methyl-4-dimethylaminoazobenzene (2-Me-DAB) and liver cell proliferation play a role in the initiation of hepatocarcinogenesis, the toxicity of 2-Me-DAB for normal and partially hepatectomized rats was investigated. Continuous feeding of a basal low protein, low riboflavin diet supplemented with 2-Me-DAB was found to be highly toxic for male albino rats. All animals fed on such a diet died before 200 days. Sham operation and partial hepatectomy (PH) at 30 days of 2-Me-DAB feeding reduced the median survival time from 122 days to 107 and 94 days, respectively. Transfer to the basal diet after 30 days of 2-Me-DAB feeding and PH prolonged the median survival time to 216 days while 97% of the rats returned to the normal complete diet after the same treatments survived for more than 300 days. 2-Me-DAB was not necrogenic and there was no evidence of reparative proliferation or hepatic tumor formation in any group. Feeding rats with the 2-Me-DAB containing diet for 1 month delayed and strongly inhibited the mitotic response of the liver to the stimulus of partial hepatectomy. This is the result of a blockage of the cells in G1 as revealed by the fact that only 1% of the hepatocytes became labeled when 2-Me-DAB fed animals were injected with tritiated thymidine prior to sacrifice at 24 h post-hepatectomy, as compared to 40% in rats fed the normal or the control basal diet. This inhibitory effect of 2-Me-DAB is reversible however since rats returned to the normal diet for 1 or 2 months after 2-Me-DAB feeding showed percentages of mitoses and labeling indices comparable to those of control animals following PH. The number of abnormal mitoses was high (13%) in regenerating livers of rats fed 2-Me-DAB and the lesions responsible for this effect are apparently not repaired since 2-Me-DAB fed rats partially hepatectomized after being transferred to the normal diet for 1 or 2 months showed the same number of mitotic irregularities. The present results suggest that assays with 2-Me-DAB as 'pure initiator' or agent of selective toxicity should be pursued in attempts to improve existing experimental models of hepatocarcinogenesis.     

Acceleration of the onset of liver regeneration by carnitine in partially hepatectomized rats

Immediately and 6 h after removal of 70% of the liver tissue, rats were treated with L-carnitine (Carnitene, Sigma-Tau, Italy) and received an injection of 100, 200 or 1,000 mg/kg b.w. into their femoral vein. The control rats were given the same volume of saline solution. The rats were sacrificed 18, 21, 24 or 30 h after the operation. The development of liver regeneration was evaluated from the incorporation of 14C-thymidine into DNA and from the hepatocyte mitiotic activity. In rats given carnitine in a dose of 100 or 200 mg/kg b.w. significantly higher DNA specific activity values were found 18 and 21 h after partial hepatectomoy and higher hepatocyte mitotic activity values after 30 h. In rats given carnitine in a dose of 1,000 mg/kg b.w., DNA specific activity values 21 h after partial hepatectomy were lower than in the control group. We conclude that L-carnitine, in a dose of 100 or 200 mg/kg b.w. has an enhancing effect on the onset of liver regeneration after 70% hepatectomy.     

Effect of parenteral administration of carnitine on liver regeneration in partially hepatectomized rats

Male Wistar rats were subjected to 65-70% hepatectomy and either immediately or 18 h after surgery were given a 6-hour infusion containing 3 ml of either Ringer solution or aqua pro injectione alone or with L-carnitine in doses 8 mg (12.4 mumol), 40 mg (62 mumol) and 200 mg (310.2 mumol)/kg b.w. The rats were killed 6, 18, 24 and 30 h after surgery. The changes in the DNA specific activity and in the mitotic activity demonstrate that L-carnitine has a stimulating, dose-dependent effect on liver regeneration. This effect acts both during early post-hepatectomy, the prereplicative period and in the subsequent replicative period.     

Zinc-binding protein in the livers of neonatal, normal and partially hepatectomized rats.

In the livers of rats after partial hepatectomy the zinc concentration began to increase soon after the operation, reached a maximum value at 14h, and decreased to the original value by 25h after the operation. In contrast, the plasma zinc concentration continued to decrease during the first 10h after the operation and remained depressed for at least 28h. The plasma and hepatic zinc concentrations were relatively unaffected by sham-operation. Synchronous with the increase in the hepatic zinc concentration after the partial hepatectomy, there was an appearance of zinc-binding protein (Zn-binding protein) in the liver cytosol. Studies with small doses of actinomycin D and cycloheximide suggest that both RNA and protein syntheses are necessary for the induction of Zn-binding protein after partial hepatectomy. A high content of the Zn-binding protein was found in neonatal rat liver. The Zn-binding protein, however, was undetectable 40 days after birth. The Zn-binding protein was also found in the adult rat liver when stimulated to proliferate after the administration of isoprenaline followed by glucagon. These findings indicate a close linkage between the appearance of Zn-binding protein in the liver cytosol and the regulation of DNA synthesis.