Changes in hepatic nitrogen metabolism in isolated perfused liver during the development of thioacetamide-induced cirrhosis in rats.
ABSTRACT Changes in hepatic nitrogen metabolism in isolated perfused liver were studied during the induction of experimental cirrhosis by thioacetamide in female Sprague-Dawley rats. Cirrhosis of the micronodular type developed during 12-week administration of thioacetamide. Despite an increase in food consumption for 4 weeks after the end of administration, the physiological changes characteristic of cirrhosis were maintained. The rate of urea excretion per unit liver weight was significantly decreased compared with pair-fed control rats both during and after thioacetamide treatment. During 4 weeks of thioacetamide treatment, the rate of urea production in perfused liver from a combination of 0.25 mM NH4Cl and 1 mM glutamine decreased slightly, without a decrease in the maximum rate of urea production from 10 mM NH4Cl. In cirrhotic rats, the rate of urea production in perfused liver from NH4Cl and/or glutamine decreased, with a decrease in the maximum rate of urea production. The Km of ureagenesis for NH3 was unchanged in cirrhotic livers. During 4 weeks of thioacetamide treatment, glutamate dehydrogenase activity decreased, but the thioacetamide-induced cirrhotic state had no effect on glutamate dehydrogenase or glutaminase activity. Glutamine synthetase activity was decreased in rats treated with thioacetamide for 4 or 12 weeks. These results are consistent with the hypothesis that the capacity for urea production from NH3 and amino acids is decreased in the development of cirrhosis.
- SourceAvailable from: Afaf SalehWorld Journal of Pharmacy and Pharmaceutical Sciences. Impact Factor 2.786. 11/2014; 3(12):138 -167.
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ABSTRACT: A better understanding of the hepatic metabolic pathways affected by fulminant hepatic failure (FHF) would help develop nutritional support and other nonsurgical medical therapies for FHF. We used an isolated perfused liver system in combination with a mass-balance model of hepatic intermediary metabolism to generate a comprehensive map of metabolic alterations in the liver in FHF. To induce FHF, rats were fasted for 36 hours, during which they received 2 D-galactosamine injections. The livers were then perfused for 60 minutes via the portal vein with amino acid-supplemented Eagle minimal essential medium containing 3% wt/vol bovine serum albumin and oxygenated with 95% O(2)/5% CO(2). Control rats were fasted for 36 hours with no other treatment before perfusion. FHF rat livers exhibited reduced amino acid uptake, a switch from gluconeogenesis to glycolysis, and a decrease in urea synthesis, but no change in ammonia consumption compared with normal fasted rat livers. Mass-balance analysis showed that hepatic glucose synthesis was inhibited as a result of a reduction in amino acid entry into the tricarboxylic acid cycle by anaplerosis. Furthermore, FHF inhibited intrahepatic aspartate synthesis, which resulted in a 50% reduction in urea cycle flux. Urea synthesis by conversion of exogenous arginine to ornithine was unchanged. Ammonia removal was quantitatively maintained by glutamine synthesis from glutamate and a decrease in the conversion of glutamate to alpha-ketoglutarate. Mass-balance analysis of hepatic metabolism will be useful in characterizing changes during FHF, and in elucidating the effects of nutritional supplements and other treatments on hepatic function.Hepatology 09/2001; 34(2):360-71. · 12.00 Impact Factor
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ABSTRACT: Drug discovery and development consists of a series of processes starting with the demonstration of pharmacological effects in experimental cell and animal models and ending with drug safety and efficacy studies in patients. A main limitation is often the unacceptable level of toxicity with the liver as the primary target organ. Therefore, approaches to study hepatic toxicity in the early phase of drug discovery represent an important step towards rational drug development. A variety of in vitro liver models have been developed in the past years. Next to their use in drug development, they can also be applied to study environmental toxins and their hepatotoxicity. The 3 main approaches are ex vivo isolated and perfused organ models, precision-cut liver slices and cell culture models. Although the advantage of whole organ perfusions is based on the assessment of physiologic parameters such as bile production and morphologic parameters such as tissue histology, cell culture models can be efficiently used to assess cellular metabolism, cytotoxicity and genotoxicity. The advantage of precision-cut liver slices is based on the juxtaposition of cellular assays and tissue morphology. None of these models can be compared as they all focus on different fields of hepatoxicology. For the future, the ideal setup for testing the hepatic toxicity of a new compound could of primary studies in cell or slice cultures to assess cellular effects and secondary studies using ex vivo perfused organs to examine gross organ function parameters and histology.Toxicologic Pathology 01/2002; 30(3):394-9. · 2.06 Impact Factor