Year: 2011
Type: dissertation
Abstract: Due to seasonal variations in temperature and food availability, fish in temperate regions\nshould be able to make metabolic adjustments to ensure that enough energy is available\nfor the maintenance of basal processes. The major aim of this thesis was to elucidate how\nthe physiology and lipid metabolism of salmonid fish is affected by temperature and food\navailability, and to clarify aspects of the endocrine control of lipid metabolism.\nIn this thesis, the effects of increased temperature or reduced food availability were\nstudied in salmonids by employing a non-prejudiced metabolomics approach to assess the physiological responses. Detailed information on the abundance of specific amino acids, lipid classes, fatty acids and other metabolites in tissue extracts and plasma was obtained by nuclear magnetic resonance (NMR) based metabolomics. NMR-based metabolomics\nwere successfully employed and proved to be applicable to studying metabolic fluxes in\nfish, providing data on novel and integrated responses. The results show similar changes\nin lipid metabolism during food deprivation and elevated temperature. The observed\nresponses included increased plasma very-low-density lipoprotein (VLDL) and\nunsaturated fatty acids (FAs) concurrent with decreased high-density lipoprotein (HDL)\nand choline. The changes during starvation also involved changes in amino acids and\nglycogen that indicate that amino acids are used for gluconeogenesis in the liver to\npreserve glycogen stores.\nGrowth hormone (GH) has both lipolytic and lipogenic effects. To further elucidate the\nmechanisms of GH action on salmonid lipid metabolism, the effects of GH in vivo on the\ntranscription of several key lipid metabolism enzymes in various tissues were investigated.\nGH inhibited the hepatic expression of lipoprotein lipase (LPL) thereby decreasing\nhepatic lipid uptake. Hormone-sensitive lipase (HSL) mRNA expression was not\nincreased by GH in any of the studied tissues, suggesting that the well-known GHinduced\nlipolysis is regulated on posttranslational levels in rainbow trout. The regulation\nlipid metabolism in salmonids was further investigated by studying direct effects of FAs\nand ghrelin on freshly isolated cells from mesenteric adipose tissue and liver. FAs elicited acute negative effects on lipid storage by decreasing lipid uptake via LPL activity in\nadipose cells as well as by stimulating lipolysis of stored triglycerides (TG) in liver cells.\nTogether the results presented in this thesis shows that elevated, suboptimal temperature\nand nutritional may have propound effects on important processes as growth, food intake\nand the metabolome of salmonid fish, and may lead to a negative energy balance.\nMetabolic changes may be mediated by hormonal and nutrient factors acting at gene\nexpression or enzyme activity level. The results may contribute to better understand lipid deposition patterns in farmed fish and potential effects of climate change on salmonids in the wild and in aquaculture.
Author: Andreas Kullgren
Language: English
Subfield: Aquatic Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1602098899