Effects Of Dietary Cholesterol And Interaction Between Cholesterol And Phospholipid On Feed Intake, Growth Performance And Cholesterol Metabolism In Juvenile Turbot (scophthalmus Maximus L.)

The study was conducted on the juvenile turbot (Scophthalmus maximus L.), oneof main industrialized fish species cultured in northern China. To illuminate theeffects of dietary cholesterol and interaction between cholesterol and phospholipid onfeed intake, growth performance and cholesterol metabolism in juvenile turbot, maincontents and results of the study are as follows:1. Feed intake, growth performance and cholesterol metabolism in juvenile turbot(Scophthalmus maximus L.) fed defatted fish meal diets with graded levels ofcholesterolA10-week growth trial was conducted to examine the effects of dietarycholesterol on feed intake, growth performance and cholesterol metabolism injuvenile turbot (Scophthalmus maximus L.)(initial body weight5.18±0.01g). Fiveisonitrogenous and isolipidic experimental diets were formulated withsupplementation of0.0,0.5,1.0,1.5and2.0%cholesterol, and the final dietarycholesterol concentrations were0.38,0.76,1.30,1.80and2.22%, respectively. WGRof fish fed diets with1.30,1.80and2.22%cholesterol was significantly higher thanthat of fish fed the diet with0.38%cholesterol, but no significant differences of WGR were found among fish fed diets with1.30,1.80and2.22%cholesterol. Also nosignificant differences were found in feed intake (FI) in all treatments. With dietarycholesterol increasing, a general upward trend of total cholesterol (TC), freecholesterol (FC), cholesterol ester (CE), high-density lipoprotein cholesterol (HDL-C)and low-density lipoprotein cholesterol (LDL-C) in serum was exhibited. However,these kinds of cholesterol in serum were plateaued when fish fed diets withapproximately over1.30to1.80%cholesterol. The results of TC in liver and fecesshowed that, with increasing dietary cholesterol, only TC in feces exhibited anincreasing trend. Quantitative PCR (qPCR) was used to assess the effects of dietarycholesterol on rate limiting enzyme3-hydroxy-3-methylglutaryl-Coenzyme A(HMG-CoA) reductase in cholesterol synthesis and cholesterol7α-hydroxylase(CYP7A1) in bile acid synthesis. HMG-CoA reductase expression in liver wassignificantly suppressed with increasing dietary cholesterol, while CYP7A1expression in liver was significantly enhanced as dietary cholesterol increased. Therewere no significant differences of ghrelin expression in both gut and brain. It can beconcluded that moderate dietary cholesterol was beneficial to growth performance,while feed intake promotion effect was limited in juvenile turbot in the present study.Feedback control might exist in the cholesterol metabolism of turbot to keepcholesterol in homeostasis.2. Effects of the interaction between dietary cholesterol and phospholipid on feedintake, growth performance and cholesterol metabolism in juvenile turbot (Scophthalmus maximus L.)A10-week growth trial was conducted to examine the effects of interactionbetween dietary cholesterol and phospholipid on feed intake, growth performance andcholesterol metabolism in juvenile turbot (Scophthalmus maximus L.)(initial bodyweight5.18±0.01g). Nine isonitrogenous and isolipidic experimental diets wereformulated to supplement three levels of cholesterol (0.0,1.0and2.0%) and threelevels of phospholipid (0.0,2.0and4.0%). Significant interaction between cholesteroland phospholipid on weight gain rate was shown in the present study (P<0.05), andthe weight gain rate increased significantly with increasing dietary cholesterol.However, no significant interaction between cholesterol and phospholipid was shownin feed intake (P>0.05). Final body composition was not significantly affected by theinteraction between cholesterol and phospholipid as well, only body lipid contentexhibited an significant upward trend with increasing dietary cholesterol. With theexception of HDL-C and LDL-C, kinds of cholesterol (total cholesterol, freecholesterol and cholesterol ester) in serum were all not significantly affected by theinteraction between dietary cholesterol and phospholipid (P>0.05). Furthermore,HDL-C and LDL-C in serum were enhanced by dietary cholesterol while suppressedby dietary phospholipid generally. No interaction between dietary cholesterol andphospholipid was found in terms of HMG-CoA reductase and CYP7A1geneexpression (P>0.05), which were only significantly suppressed and enhanced bydietary cholesterol respectively. Regarding to the orexigenic factor Ghrelin geneexpression, only Ghrelin expressed in intestine was significantly affected by the interaction between dietary cholesterol and phopholipid (P<0.05). It could beconcluded that the interaction between dietary cholesterol and phospholipidsignificantly affected the HDL-C and LDL-C in terms of cholesterol transportation,while no significant interaction was found on cholesterol synthesis and degradation,such as HMG-CoA reductase and CYP7A1, which indicated that phospholipid playedan important role in cholesterol transportation.