Changes in hepatic nitrogen metabolism in isolated perfused liver during the development of thioacetamide-induced cirrhosis in rats

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 K-m 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. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.