Increasing levels of dietary crystalline methionine affect plasma methionine profiles, ammonia excretion, and the expression of genes related to the hepatic intermediary metabolism in rainbow trout (Oncorhynchus mykiss).
Strictly carnivorous fish with high requirements for dietary protein, such as rainbow trout (Oncorhynchus mykiss) are interesting models for studying the role of amino acids as key regulators of intermediary metabolism. Methionine is an essential amino acid for rainbow trout, and works as a signalling factor in different metabolic pathways. The study investigated the effect of increasing dietary methionine intake on the intermediary metabolism in the liver of juvenile rainbow trout. For this purpose, five diets were formulated with increasing methionine levels from 0.60 to 1.29% dry matter. The diets were fed in excess for six weeks before three sampling campaigns carried out successively to elucidate (i) the hepatic expression of selected genes involved in lipid, glucose and amino acid metabolism; (ii) the postprandial ammonia excretion; and (iii) the postprandial plasma methionine concentrations. The transcript levels of enzymes involved in lipid metabolism (fatty acid synthase, glucose 6 phosphate dehydrogenase and carnitine palmitoyl transferase 1 a), gluconeogenesis (fructose-1,6-biphosphatase) and amino acid catabolism (alanine amino transferase and glutamate dehydrogenase) were significantly affected by the increase in dietary methionine. Changes in gene expression reflected to some extent the decrease in ammonia excretion (P=0.022) and in the hepatosomatic index (HSI; P<0.001) when dietary methionine increased. Postprandial plasma methionine concentrations correlated positively with the dietary level (P<0.001) at the different sampling points. The study shows that the expression of several genes related to the hepatic intermediary metabolism in rainbow trout responded in a dose-dependent manner to increasing levels of dietary methionine.
BioMar A/S, Mylius Erichsensvej 35, DK -7330 Brande, Denmark; Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Center, P.O. Box 101, DK -9850 Hirtshals, Denmark. Electronic address: rollandmarine@laposte.net.
Marine
M
Rolland
Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Center, P.O. Box 101, DK -9850 Hirtshals, Denmark.
Peter V
PV
Skov
Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Center, P.O. Box 101, DK -9850 Hirtshals, Denmark.
Bodil K
BK
Larsen
BioMar A/S, Mylius Erichsensvej 35, DK -7330 Brande, Denmark.
Jørgen
J
Holm
BioMar A/S, Mylius Erichsensvej 35, DK -7330 Brande, Denmark.
Pedro
P
Gómez-Requeni
Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Center, P.O. Box 101, DK -9850 Hirtshals, Denmark.
Johanne
J
Dalsgaard
D000641:Ammonia / Q000378:metabolism*; D000818:Animals; D004032:Diet; D005786:Gene Expression Regulation / Q000187:drug effects*; D005943:Gluconeogenesis / Q000187:drug effects; D050356:Lipid Metabolism / Q000187:drug effects; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008715:Methionine / Q000097:blood* / Q000737:chemistry / Q000494:pharmacology*; D017686:Oncorhynchus mykiss / Q000097:blood / Q000235:genetics / Q000378:metabolism*
D000641:Ammonia; D008715:Methionine
Amino acid catabolism; Crystalline amino acid; Gluconeogenesis; Hepatic gene expression; Hepatosomatic index; Lipid metabolism