| Metabolism of fatty acids has become a hot research topic in fish nutrition. Fatty acids arethe main source of energy for the body’s tissues, and L-carnitine is essential on the normalmetabolism of fatty acids. Long chain fatty acids on outer membrane of mitochondrial can notbe used for β-oxidation freely only by L-carnitine mediate, the process is an importantregulatory site of fatty acids oxidation in mitochondrial. Carnitine palmitoyltransferase I (CPT I)is the main regulatory enzyme in mitochondrial fatty acids oxidation. However, the research ofL-carnitine on gene regulation of enzymes for fatty acids metabolism in fish is less and therelationship between L-carnitine and CPT I activities is not clear enough. There are no studieswith effects of supplementing L-carnitine on CPT I gene expression in common carp (Cyprinuscarpio).Therefore, it was the purpose of present research to investigate the role of supplementingL-carnitine on fatty acids metabolism in the mitochondria of common carp (Cyprinus carpio):effects of supplementing L-carnitine on growth performance, body composition, plasmabiochemical indexes, enzyme activities and gene expression of fatty acids metabolism incommon carp juvenile on levels of the apparent traits, tissue signatures and cell regulation.By the following experimental design and a series of experiment, the results are asfollows:（1）Effects of L-carnitine on growth performance, body composition and plasmabiochemical indexes of common carp juvenile were studied to offer theoretical basis to addingL-carnitine. Six dietary treatments contained L-carnitine concentrations of0,50,100,150,200,400mg/kg were fed to apparent satiation third daily to triplicate groups of initially weighting(2.5±0.5) g per fish for sixty days. At the end of the feeding trial, growth rate, specific growthrate (SGR), feed conversion ratio (FCR), survival, muscle composition, triglyceride (TG),cholesterol (CHO), Albumin, Urea nitrogen (BUN) were determined.Result is showed that growth rate and SGR were significantly improved and FCR wassignificantly (P＜0.05) lower by feeding200mg/kg L-carnitine.No significant (P＞0.05)difference in survival rate.Lipid content decreased significantly (P＜0.05) in the dorsal musclewhereas protein content increased significantly (P＜0.05) with the addition of dietaryL-carnitine. Compared with the control group, lipid content decreased by12.65%and proteincontent increased by11.18%by feeding200mg/kg L-carnitine, but no significant (P＞0.05)difference than adding400mg/kg L-carnitine. TG, CHO, BUN that supplemented with L-carnitine was significantly (P＜0.05) decreased and Albumin was significantly (P＜0.05)increased. CHO was lowest by feeding150mg/kg L-carnitine and TG was lowest by feeding50mg/kg L-carnitine, compared with the control group, respectively decreased by36.08%and50.28%. BUN was lowest whereas Albumin was highest by feeding200mg/kg L-carnitine,respectively was13.49mmol/L and9.12g/L, decreased by17.49%and increased by32.56%that of the control group, but no significant (P＞0.05) difference between the groups. Weconclusion that under the condition of this experiment, adding L-carnitine will promote thegrowth parameters of common carp juvenile and reduce lipid content of tissue and plasma. Theoptimal dose of L-carnitine in common carp juvenile diet was suggested to be200mg/kg.（2）To investigate effects of L-carnitine on the fatty acids composition of white muscleand hepatopancreas in common carp, samples of white muscle and hepatopancreas wereextracted to detect fatty acids composition. Result is showed that fatty acids composition wereaffected significantly (P＜0.05) by feeding L-carnitine.∑SFA and∑MUFA contents weresignificantly (P＜0.05) higher by feeding L-carnitine than those of the control group, but∑PUFA, EPA, DHA,∑n-3and∑n-6were significantly (P＜0.05) lower; The fatty acidscomposition were affected significantly by feeding150mg/kg L-carnitine. L-carnitine make theexploit of PUFA of the white muscles in juvenile carp greater than synthesis of PUFA, EPA,DHA strengthen fatty acids metabolism.（3）To investigate effects of L-carnitine on fatty acids metabolism-related enzymeactivity in common carp, samples of hepatopancreas were extracted for detect enzyme activities.Result is showed that FAS activity was significantly (P＜0.05) by feeding L-carnitine than thoseof the control group, but LPL, HL, TL, CPT I activities were significantly (P＜0.05) lower. Theenzyme activities were affected significantly by feeding150mg/kg L-carnitine.（4）White muscle total RNA were extracted from common carp, CPT I gene wasamplified and cloned using RT-PCR. The partial cDNA of CPT I gene was cloned for the firsttime (GenBank accession number JQ361077), and the homologous alignment was analyzed. Theobtained cDNA sequence was857bp in length, and its homology with zebra fish (Danio rerio)is89%and rainbow trout (Oncorhynchus mykiss) is79%. CPT I gene showed a higherconservatism.（5）Six tissue total RNA were extracted from common carp, CPT I gene was amplifiedand cloned. The expression in different organs of CPT I was detected in common carp with themethods of RT-PCR. The influence of dietary L-carnitine on the gene expression of CPT I inwhite muscle of common carp was also studied. It is revealed that CPT I is widely expressed inhepatopancreas, heart, red muscle, white muscle, kidney, intestine, with the highest expression level observed in heart, lowest in white muscle, intestine and hepatopancreas. After sixty daysfeeding with L-carnitine contained diet, the expression level of CPT I was significantly higherthan other groups by feeding150mg mg/kg L-carnitine, four times that of the control group.CPT I is mainly express in high energy generating tissues and its expression level described ascould be regulated by L-carnitine.This study provides theoretical basis to clarify the mechanism of L-carnitine on fatty acidsmetabolism and technical support to the development feed, guide rational use of L-carnitine infish farming. |
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