title: Atlantic salmon (Salmo salar) fed L-carnitine exhibit altered intermediary metabolism and reduced tissue lipid, but no change in growth rate.
abstract: Metabolic evidence was sought to explain the reduced body fat and increased body protein observed in Atlantic salmon fed diets supplemented with L-carnitine. By stimulating fatty acid oxidation, dietary carnitine might increase flux through pyruvate carboxylase and decrease flux through the branched-chain alpha-keto acid dehydrogenase complex, by increasing regulatory ratios of acetyl CoA:free enzyme A (CoA-SH) and ATP:ADP. Such changes could conserve nitrogen by providing more carbon for amino acid biosynthesis and by blocking oxidative loss of the branched-chain amino acids. Consistent with this hypothesis, salmon fed carnitine (23 mmol/kg diet) for 9 wk exhibited greater metabolic rates than cohorts fed a carnitine-free diet (P < 0.05) for the following: 1) 1-[14C] palmitate oxidation by liver cubes (48%) and by isolated hepatocytes (151%), 2) pyruvate-dependent [14 CO2]-fixation by isolated mitochondria (81%), 3) incorporation of 1-[14C] lactate into glucose by liver cubes (120%) and by isolated hepatocytes (210%), and 4) incorporation of [35S]-methionine into the acid-insoluble fraction of liver cubes (59%) and isolated hepatocytes (89%). Hepatic concentrations of seven amino acids, including the branched-chain amino acids, were greater (7-112%), as were the plasma concentrations of three of these (45-130%). However, 230% more enzyme in the mitochondria of carnitine-fed fish, and not a difference in the ratios of acetyl CoA:CoA-SH or ATP:ADP, appeared to account for accelerated flux through pyruvate carboxylase; flux through the dehydrogenase complex was unchanged. These results implicate induction of pyruvate carboxylase (or a reduction in turnover) and enhanced protein synthesis in the mechanism for carnitine-induced changes in gluconeogenesis and nitrogen metabolism.
authors: Department of Biochemistry, Microbiology and Molecular Genetics, University of Rhode Island, Kingston 02881, USA.
authors: H
authors: H
authors: Ji
authors: T M
authors: TM
authors: Bradley
authors: G C
authors: GC
authors: Tremblay
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001823:Body Composition / Q000187:drug effects* / Q000502:physiology; D002331:Carnitine / Q000032:analysis / Q000097:blood / Q000494:pharmacology*; D002469:Cell Separation; D004032:Diet / Q000662:veterinary*; D006003:Glycogen / Q000032:analysis / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids / Q000032:analysis; D008099:Liver / Q000737:chemistry / Q000166:cytology / Q000648:ultrastructure; D008930:Mitochondria, Liver / Q000201:enzymology; D018482:Muscle, Skeletal / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism; D010084:Oxidation-Reduction; D012474:Salmon / Q000254:growth & development* / Q000378:metabolism* / Q000502:physiology; D015430:Weight Gain / Q000502:physiology
chemical_list: D000596:Amino Acids; D008055:Lipids; D006003:Glycogen; D009584:Nitrogen; D002331:Carnitine