Atlantic salmon (Salmo salar) fed L-carnitine exhibit altered intermediary metabolism and reduced tissue lipid, but no change in growth rate

• Main Authors: Ji, Hong, Bradley, Terence M., Tremblay, George C.
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 1996
• Subjects: Atlantic salmon; body composition; carnitine; growth; pyruvate carboxylase; Salmo salar
• Online Access: https://digitalcommons.uri.edu/favs_facpubs/134; https://doi.org/10.1093/jn/126.8.1937

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 α-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 [14CO2]-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.