title: Effects of nutritional status on plasma leptin levels and in vitro regulation of adipocyte leptin expression and secretion in rainbow trout.
abstract: As leptin has a key role on appetite, knowledge about leptin regulation is important in order to understand the control of energy balance. We aimed to explore the modulatory effects of adiposity on plasma leptin levels in vivo and the role of potential regulators on leptin expression and secretion in rainbow trout adipocytes in vitro. Fish were fed a regular diet twice daily ad libitum or a high-energy diet once daily at two ration levels; satiation (SA group) or restricted (RE group) to 25% of satiation, for 8weeks. RE fish had significantly reduced growth (p<0.001) and adipose tissue weight (p<0.001), and higher plasma leptin levels (p=0.022) compared with SA fish. Moreover, plasma leptin levels negatively correlated with mesenteric fat index (p=0.009). Adipocytes isolated from the different fish were treated with insulin, ghrelin, leucine, eicosapentaenoic acid or left untreated (control). In adipocytes from fish fed regular diet, insulin and ghrelin increased leptin secretion dose-dependently (p=0.002; p=0.033, respectively). Leptin secretion in control adipocytes was significantly higher in RE than in SA fish (p=0.022) in agreement with the in vivo findings, indicating that adipose tissue may contribute to the circulating leptin levels. No treatment effects were observed in adipocytes from the high-energy diet groups, neither in leptin expression nor secretion, except that leptin secretion was significantly reduced by leucine in RE fish adipocytes (p=0.025). Overall, these data show that the regulation of leptin in rainbow trout adipocytes by hormones and nutrients seems to be on secretion, rather than at the transcriptional level.
authors.affiliation: Department of Physiology and Immunology, Faculty of Biology, University of Barcelona, Barcelona 08028, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Salmerón
authors.affiliation: Fish Endocrinology Laboratory, Department of Biological and Environmental Sciences, University of Gothenburg, 40590 Gothenburg, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Johansson
authors.affiliation: Department of Biology, University of Bergen, Bergen 5020, Norway.
authors.forename: Anna R
authors.initials: AR
authors.lastname: Angotzi
authors.affiliation: Department of Biology, University of Bergen, Bergen 5020, Norway.
authors.forename: Ivar
authors.initials: I
authors.lastname: Rønnestad
authors.affiliation: Fish Endocrinology Laboratory, Department of Biological and Environmental Sciences, University of Gothenburg, 40590 Gothenburg, Sweden.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Jönsson
authors.affiliation: Fish Endocrinology Laboratory, Department of Biological and Environmental Sciences, University of Gothenburg, 40590 Gothenburg, Sweden.
authors.forename: Björn Thrandur
authors.initials: BT
authors.lastname: Björnsson
authors.affiliation: Department of Physiology and Immunology, Faculty of Biology, University of Barcelona, Barcelona 08028, Spain.
authors.forename: Joaquim
authors.initials: J
authors.lastname: Gutiérrez
authors.affiliation: Department of Physiology and Immunology, Faculty of Biology, University of Barcelona, Barcelona 08028, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Navarro
authors.affiliation: Department of Physiology and Immunology, Faculty of Biology, University of Barcelona, Barcelona 08028, Spain. Electronic address: ecapilla@ub.edu.
authors.forename: Encarnación
authors.initials: E
authors.lastname: Capilla
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002478:Cells, Cultured; D004734:Energy Metabolism; D005786:Gene Expression Regulation; D020738:Leptin / Q000097:blood / Q000235:genetics / Q000378:metabolism; D009752:Nutritional Status / Q000502:physiology*; D017686:Oncorhynchus mykiss / Q000097:blood* / Q000235:genetics / Q000378:metabolism
chemical_list: D020738:Leptin
keywords: Adipose tissue; Ghrelin; Insulin; Leucine; Oncorhynchus mykiss; Teleost