ABSTRACTSince their discovery in the early 1990s, peroxisome proliferator-activated receptors (PPARs)have become an extremely important set of targets for drug discovery. The ligand-inducedtranscription factors that regulate the transcription of target genes in response to specificligands, keeps on broadening its repertoire as new knowledge are uncovered. PPARs arenuclear lipid-activated receptors that control a vast variety of genes in several pathways oflipid metabolism. This includes fatty acid transport, uptake by the cells, intracellular bindingand activation, as well as catabolism (â-oxidation and ù-oxidation) or storage. They areimportant pharmacological targets of treatment of obesity, diabetes and lipid disorders.Although, PPARs are among the most studied nuclear receptors, there is little knowledge oftheir activity and functions in fish. Atlantic salmon- Salmo salar L. belongs to the familySalmonidae (Salmonids) and the order Salmoniformes. Norway have traditionally beenfarming Atlantic salmon since the early 1970s, and is today one of the major producers offarmed salmon for human consumption. The quality of fish depends much on the mechanismsthat keep the fish healthy. The adipose regulations in fish are still unknown, and it is of greatinterest that they are investigated.One of the goals of this thesis was to study PPAR gene expression in Atlantic salmon. Wecompared PPAR tissue distribution in various fish tissue and cell lines. The tissue distributionof PPARs in salmon was comparable to what has been described for mammals, a higherconcentration in tissues where adipose metabolism is more relevant. We also exposed SHK-1and ASK cells (Atlantic salmon head kidney cells) to PPAR agonist treatment and found thatwhen activating PPARã, an up-regulation of target genes like SR-BI and CD 36 where seen.These target genes play a key role in regulation of cholesterol homeostasis and havepreviously been shown to be up-regulated by PPARã in mammals. To further investigatePPARã, we performed transfection studies. Although, we obtained low transfectionefficiency, the findings showed same trend in PPAR transcription activity regulation.Highly specific antibodies against fish antigens are rare. We therefore performed assays totest a novel anti salmon-PPARã antibody for specificity, applying methods such asimmunostaining and western blotting. If the PPARã antibody proved specific, it would3provide us with an important tool in PPAR studies. Unfortunately this was not the case in ourstudy.Our results of PPAR activity in Atlantic salmon head kidney cells agreed in many aspectswith previous findings in mammalian cells. However, there were low effects of ligandtreatment, and it came apparent during this work that PPAR agonists could have toxic effectson SHK-1 and ASK cells in the concentrations employed here.