Effects Of Dietary Carbohydrate On Lipid Metabolism And Ghrelin Mrna Relative Expression Level In Turbot

Turbot (Scophthalmus maximus L.), an important commercial carnivorous fish inChina, is widely farmed. The aim of these experiments was to study the lipidmetabolism and Ghrelin mRNA relative expression level effects of dietarycarbohydrate complexity, lipid and protein replacement by carbohydrate. The resultsare summarized as follows:1Molecular cloning and characterization of Ghrelin from turbotIn the present study, the cDNA of Ghrelin from turbot was cloned by homologycloning with degenerate primer and RACE techniques. The full-length cDNA ofGhrelin was of948bp, including an open reading frame (ORF) of321bp encoding amature peptide22amino acids with predicted molecular weight of2342.64u andtheoretical isoelectric point of12.02. The N-terminus of the mature peptide has a veryconservative site "GSSFLSP" may be the active center of the Ghrelin. BLASTanalysis revealed that Ghrelin shared high similarity with other known Ghrelin in fish.Phylogenetic tree analysis shows that the aquatic animals and terrestrial animalsGhrelin amino acid sequence is divided into two branches. Evolutionarily closerrelationship between turbot and large yellow croaker.2Effects of dietary carbohydrate complexity on lipid metabolism and GhrelinmRNA relative expression level in turbotThe study was conducted to study the effects of three kinds of dietary carbohydrates(glucose, sucrose and dextrin) on activities of lipid metabolism enzymes, compositionsof fatty acid and Ghrelin mRNA relative expression level in juvenile turbot. Theresults showed that activities of glucose-6-phosphate dehydrogenase and malicenzyme in liver was significantly influenced by dietary carbohydrates (P<0.05).Activities of glucose-6-phosphate dehydrogenase and malic enzyme in the treatmentwith dietary glucose were significantly higher than those in treatments with dietarysucrose or dextrin (P<0.05). Significant difference in lipase activity was found inintestine of fish fed with different carbohydrates (P<0.05). Lipoprotein lipase activityof fish fed with glucose-added diet was significantly lower than those in the othertreatments (P<0.05). Different dietary carbohydrates did not significantly affect hepatic lipase activity (P>0.05), but significantly affected total lipase activity inturbot (P<0.05). Contents of C16:0and C18:0in muscle of turbot fed with dietaryglucose were significantly higher than those fed with dietary dextrin (P<0.05), butcontents of C16:1and C18:1were significantly lower (P<0.05). In general, effects ofdietary carbohydrates on fatty acid compositions in muscle were mainly on saturatedand mono-unsaturated, not on poly-unsaturated fatty acids. The expression level ofGhrelin in stomach tissue was measured by real-time PCR. With the increase of thecomplexity of the dietary carbohydrates, Ghrelin mRNA relative expression level offish fed with glucose-added diet was significantly higher than those in the othertreatments (P<0.05).3Effects of dietary lipid replacement by carbohydrate on lipid metabolis m andGhrelin mRNA relative expression level in turbotIn order to study the effect of dietary lipid replacement by carbohydrate on lipidmetabolism and Ghrelin mRNA relative expression level in turbot. With white fishmeal, casein and gelatin as the main source of protein, fish oil and soy lecithin as themain source of lipid. Lipid was replaced by carbohydrate at four levels of0%,5%,15%,28%.The results showed that activities of glucose-6-phosphate dehydrogenasein the treatment with15%level of dextrin were significantly higher than those intreatments with dietary dextrin level of0%and5%(P<0.05). Different dextrin levelsdid not significantly affect hepatic malic enzyme activity (P>0.05). Significantdifference in lipase activity was found in intestine of fish fed with different replacelevel (P<0.05). Different dietary fish oil replacement by dextrin levels did notsignificantly affect lipoprotein lipase activity of fish (P>0.05), but significantly affecthepatic lipase activity and total lipase activity in turbot (P<0.05). The dietarycarbohydrates level significantly affect Ghrelin mRNA relative expression level inturbot (P<0.05). Carbohydrate at level of15%, Ghrelin mRNA relative expressionlevel in turbot was significantly higher than those in level of5%and28%(P<0.05),but significantly lower than the level of0%(P<0.05).4Effects of dietary protein replace ment by carbohydrate on lipid metabolis m inturbotIn order to study the effect of dietary protein replacement by carbohydrate level onactivities of lipid metabolism enzymes and compositions of fatty acid in juvenileturbot. Protein was replaced by dextrin at three levels of0%,5%and15%. The resultsshowed that activities of glucose-6-phosphate dehydrogenase and malic enzyme in liver was significantly influenced by dietary carbohydrate levels (P<0.05). With theincrease of the level of the dietary carbohydrates, lipase activity was found in intestineof fish tend to decrease. Carbohydrate at level of0%, lipase activity were significantlyhigher than those in level of15%(P<0.05), but have no significant difference than thelevel of5%(P>0.05). Different dietary protein replacement by dextrin level did notsignificantly affect lipoprotein lipase activity, hepatic lipase activity and total lipaseactivity in turbot (P>0.05). Contents of C16:1in muscle of turbot was significantlyinfluenced by dietary protein replacement by carbohydrate levels (P<0.05). Differenttreatments have no significantly effects on poly-unsaturated fatty acids and highlyunsaturated fatty acid (P>0.05).