Insulin hyperresponsiveness in partially hepatectomized diabetic rats

The present work analyzes the expression of insulin receptors and theirs related intracellular signaling molecules in partially hepatectomized-diabetic rats. Insulin binding through Scatchard analysis was studied using isolated hepatocytes of Control (Sham-operated), Hepatectomized, Diabetic and Diabetic-Hepatectomized male Wistar rats. In a set of in vivo experiments, the levels of alpha subunit of the insulin receptor, the insulin receptor substrate 1 (IRS-1) and the phosphatidylinositol 3-kinase (PI3K) were determined. [3H]-thymidine incorporation into DNA 24 or 48 h after surgery was assessed in all the experimental groups. Scatchard analysis showed that insulin receptor number was increased in diabetic and in hepatectomized rats in the same extent (64%, with respect to Controls). Diabetic-hepatectomized rats showed a dramatic increase of the receptor concentration (400%) and on the affinity constant (532%). Besides, the insulin receptor expression was increased in the treated groups, being the higher values those of the diabetic-hepatectomized rats. IRS-1 and PI3K showed similar increases. DNA synthesis was not impaired by the diabetes state. In conclusion, increased expression of IR and IRS-1 leads to increased association of PI3K in vivo in diabetic regenerating rats. The enhancement of this pathway may reveal an insulin hyperresponsiveness in these animals.     

Carbon tetrachloride metabolism in partially hepatectomized and sham-operated rats pre-exposed to chlordecone (Kepone)

The potentiation of CCl4 toxicity by pre-exposure to chlordecone (CD) is well established. Chlordecone-induced metabolism of CCl4 and suppressed hepatocellular repair have been offered as possible mechanisms for this potentiation. Recent work using the partially hepatectomized (PH) rat as a model for an actively regenerating liver has provided supportive evidence for the latter hypothesis. The present study was initiated to determine if metabolism and disposition of 14CC14 is altered in the PH rat, and if this is a contributing factor to the reported protective effect afforded by the PH procedure. Male Sprague-Dawley rats (150-175 g) maintained on dietary CD (10 ppm) for 15 days were partially hepatectomized or sham-operated (SH) on day 15. Another group of CD-pretreated rats received 0.9% CoCl2 (60 mg/kg, sc, qd for 2 days) in lieu of the surgical procedure. On day 16 the rats were challenged with a single dose of CCl4 (100 microL/kg, ip) containing 20 muCi 14CCl4. A radiolabel inventory consisting of exhaled 14CCl4, 14CO2 production, total hepatic 14C, free 14CCl4 and covalently bound 14C was taken over a 6-hr time period. Lipid peroxidation and serum enzyme activities [aspartate aminotransferase (AST) and alanine aminotransferase (ALT)] were measured in indices of toxicity. Neither CD pretreatment alone nor CoCl2 treatment alone produced significant alterations in metabolism of low dose (100 microliters/kg) CCl4. No significant difference in 14CCl4 recovery or 14CO2 production was detected for PH versus SH rats. Hepatic 14CCl4-derived 14C (per gram tissue) was greater in PH rats. Values for free 14CCl4, covalently bound 14C, and lipid peroxidation were similar for SH and PH rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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.