| 1. |
- Björn van Praagh, Helena, et al.
(författare)
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Metabolic fate of C-14-labelled chlorinated and non-chlorinated fatty acids in goldfish (Carassius auratus)
- 2004
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Ingår i: Fish Physiology & Biochemistry. - : Springer Science and Business Media LLC. - 0920-1742 .- 1573-5168. ; 30:1, s. 13-20
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the metabolic fate of chlorinated fatty acids in fish, goldfish were fed either 9,10-dichlorostearic acid or oleic acid, chosen as the unchlorinated analogue, both radiolabelled at either the carboxyl (1st) or the terminal (18th) carbon of the fatty acid chain. By keeping the fish in hermetically closed aquaria, all the respired, assimilated and excreted radioactivity could be accounted for. Fish fed 9,10-dichlorostearic acid labelled in the terminal end respired radioactive CO2 to a much lower degree than fish fed the other test compounds. As a consequence, the radioactivity bound in lipids was higher in the group of fish fed dichlorostearic acid labelled in the terminal end. It is suggested that the chlorine atoms in the middle of the carbon chain obstruct the metabolic turn-over of 9,10-dichlorostearic acid, which may have an impact on the residence time of these compounds in the ecosystem.
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| 2. |
- Björnsson, Björn Thrandur, 1952, et al.
(författare)
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Growth hormone endocrinology of salmonids: regulatory mechanisms and mode of action
- 2002
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Ingår i: FISH PHYSIOLOGY AND BIOCHEMISTRY. - 0920-1742. ; 27:3-4, s. 227-242
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Tidskriftsartikel (refereegranskat)abstract
- The focus of this review is on the regulatory mechanisms and the mode of action of GH in salmonids. To stimulate further research, it aims at highlighting areas where numerous important breakthroughs have recently been made, as well as where data are currently lacking. The regulation of GH secretion is under complex hypothalamic control, as well as under negative feedback control by GH and IGF-I. Further, the recently characterized ghrelin is a potent GH secretagogue, and may prove to be a link between feed intake and growth regulation. GH plasma profiles show indications of diurnal changes, but whether salmonids have true pulsatile GH secretion remains to be elucidated. The recent cloning and characterization of the salmon GH receptor (GHR) is a major research break-through which will give new insights into the mechanisms of GH action. It should also stimulate research into circulating GH-binding proteins (GHBPs), as they appear to be a soluble form of the GHR. The salmonid GHR sequences show evolutionary divergence from other fish species, but with a high degree of identity within the salmonid group. Radioreceptorassay studies have found GHR present in all tissues examined, which is in line with the highly pleiotropic action of GH. Data are currently scarce on the plasma dynamics of GH in salmonids, and further studies on GHR and GHBPs dynamics coupled to assessments of GH clearance rates and pathways are needed. The direct versus indirect nature of GH action remains to be clarified, but GH appears to act both locally at the target tissue level to stimulate the autocrine/paracrine action of IGF-I, as well as on the liver to increase plasma IGF-I levels. In addition, GH interacts with other hormones such as cortisol, thyroid hormones, insulin, and reproductive hormones, generating a wide range of physiological effects. GH may act both peripherally and directly at the level of the central nervous system to modify behavior, probably by altering the dopaminergic activity in the brain.
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| 3. |
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| 4. |
- Ebbesson, Lars O.E., et al.
(författare)
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Free plasma thyroxine levels in coho salmon, Oncorhynchus kisutch, during parr-smolt transformation : Comparison with total thyroxine, total triiodothyronine, and growth hormone levels
- 2000
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Ingår i: Fish Physiology and Biochemistry. - 0920-1742. ; 22:1, s. 45-50
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Tidskriftsartikel (refereegranskat)abstract
- Free plasma thyroxine (FT4) levels were measured in coho salmon, Oncorhynchus kisutch, during parr-smolt transformation (smoltification) using an equilibrium dialysis system followed by a radioimmunoassay. The FT4 data were correlated to total plasma thyroxine (TT4), triiodothyronine (TT3), and growth hormone (GH). Plasma samples were taken weekly from early April to late May, when the salmon where released from the hatchery. Free thyroxine and GH levels increased gradually through smoltification. TT4 levels increased significantly in mid-April and in mid-May. TT3 levels increased in April and remained elevated until late-May after which they declined to the lowest levels. During the first increase in TT4 levels, FT4 levels remained low and TT3 levels did not increase until FT4 levels increased in late-April. In addition, after TT4 levels decreased in late May, FT4 levels remained elevated. These data show that there are differences between the plasma FT4 and TT4 profiles during smoltification. Nevertheless, regression analysis indicates that FT4 levels are highly correlated to the increases in the levels of GH (r=0.73) and TT4 (r=0.70). In addition, GH is less correlated to TT4 and TT3 (r = 0.24 and r = -0.46, respectively) compared with FT4 (r = 0.73), suggesting a close relationship between the increases of FT4 and GH. In addition, these data suggest that this method of measuring free plasma thyroxine may provide a new tool for studying the timing of thyroid hormone action and regulation during parr-smolt transformation in salmonids.
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