title: The urea cycle and related pathways in the liver of Walker-256 tumor-bearing rats.
abstract: The urea cycle was evaluated in perfused livers isolated from cachectic tumor-bearing rats (Walker-256 tumor). Urea production in livers of tumor-bearing rats was decreased in the presence of the following substrates: alanine, alanine + ornithine, alanine + aspartate, ammonia, ammonia + lactate, ammonia + pyruvate and glutamine. Urea production from arginine was higher in livers of tumor-bearing rats. No difference was found with aspartate, aspartate + ammonia, citrulline, citrulline + aspartate and glutamine + aspartate. Ammonia consumption was smaller in livers from cachectic rats when the substance was infused together with lactate and pyruvate. Glucose production was smaller in the cachectic condition only when alanine was the gluconeogenic substrate. Blood urea was higher in tumor-bearing rats, suggesting higher rates of urea production. The availability of aspartate seems to be critical for urea synthesis in the liver of tumor-bearing rats, which is possibly unable to produce this amino acid in sufficient amounts from endogenous sources. The liver of tumor-bearing rats may have a different exogenous substrate supply of nitrogenous compounds. Arginine could be one of these compounds in addition to aspartate which seems to be essential for an efficient ureogenesis in tumor-bearing rats.
authors.affiliation: Laboratory of Liver Metabolism, Department of Biochemistry, University of Maringá, 87020900 Maringá, Brazil.
authors.forename: Sandra Regina
authors.initials: SR
authors.lastname: Corbello Pereira
authors.forename: Elaine
authors.initials: E
authors.lastname: Darronqui
authors.forename: Jorgete
authors.initials: J
authors.lastname: Constantin
authors.forename: Mário Henrique da Rocha Alves
authors.initials: MH
authors.lastname: da Silva
authors.forename: Nair Seiko
authors.initials: NS
authors.lastname: Yamamoto
authors.forename: Adelar
authors.initials: A
authors.lastname: Bracht
mesh_terms: D000409:Alanine / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002100:Cachexia / Q000209:etiology / Q000378:metabolism; D002279:Carcinoma 256, Walker / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D010101:Oxygen Consumption; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D014508:Urea / Q000378:metabolism*
chemical_list: D000641:Ammonia; D014508:Urea; D000409:Alanine