| 1. |
- Jones, V. J., et al.
(författare)
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The influence of Holocene tree-line advance and retreat on an arctic lake ecosystem : a multi-proxy study from Kharinei Lake, North Eastern European Russia
- 2011
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Ingår i: Journal of Paleolimnology. - : Springer. - 0921-2728 .- 1573-0417. ; 46:1, s. 123-137
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Tidskriftsartikel (refereegranskat)abstract
- A consequence of predicted climate warming will be tree-line advance over large areas of the Russian tundra. Palaeolimnological techniques can be used to provide analogues of how such changes in tree-line advance and subsequent retreat affected lake ecosystems in the past. A Holocene sediment core taken from Kharinei Lake (Russia) was dated radiometrically and used for multi-proxy analyses with the aim of determining how climate and tree-line dynamics affected the productivity, community structure, carbon cycling and light regime in the lake. Pollen and macrofossil analyses were used to determine the dates of the arrival and retreat of birch and spruce forest. C:N ratios and percent loss-on-ignition were used to infer past changes in sediment organic matter. Visible-near-infrared spectroscopy and diatom analysis were used to infer past changes in lake-water carbon. Algal pigments and aquatic macrophytes were used to determine changes in lake productivity and light. Chironomids together with remains of the aquatic flora and fauna were used to provide information on past July temperature and continentality. Lake sedimentation was initiated shortly before 11,000 cal. years BP, when both chironomid- and pollen-inferred temperature reconstructions suggest higher summer temperatures than present, between 1 and 2 degrees C warmer, and lake productivity was relatively high. A few trees were already present at this time. The spruce forest expanded at 8,000 cal. year BP remaining in the vicinity of the lake until 3,500 cal. year BP. This period coincided with a high concentration of organic material in the water column, and relatively high benthic productivity, as indicated by a high benthic: planktonic diatom ratio. After tree-line retreat, the optical transparency of the lake increased, and it became more open and exposed, and was thus subject to greater water-column mixing resulting in a higher abundance of diatom phytoplankton, especially heavily silicified Aulocoseira species. The colder climate resulted in a shorter ice-free period, the lake was less productive and there was a loss of aquatic macrophytes. Increased wind-induced mixing following forest retreat had a greater influence on the lake ecosystem than the effects of decreasing organic matter concentration and increased light penetration.
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| 2. |
- Virkki, Liisa M, et al.
(författare)
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Dehydroepiandrosterone (DHEA) substitution treatment for severe fatigue in DHEA-deficient patients with primary Sjögren's Syndrome.
- 2010
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Ingår i: Arthritis care & research. - : Wiley. - 2151-4658 .- 2151-464X. ; 62:1, s. 118-24
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Primary Sjögren's syndrome (SS) is characterized by fatigue and low levels of serum dehydroepiandrosterone/dehydroepiandrosterone sulfate (DHEA/DHEAS). Our aim was to study whether SS patients with severe fatigue and low serum DHEAS values benefit from DHEA substitution (50 mg/day). METHODS: A multicenter, investigator-based, powered, randomized controlled clinical trial (crossover, washout design) using fatigue as the primary outcome measure was performed on patients with primary SS (n = 107) who had a general fatigue score > or =14 on the 20-item Multiple Fatigue Inventory (MFI-20), combined with age- and sex-adjusted serum DHEAS values below the mean. Fatigue was assessed using MFI-20 subscales, i.e., general fatigue, physical fatigue, mental fatigue, reduced motivation, and activity (scale 4-20), and with a visual analog scale (VAS; scale 0-100). RESULTS: In an intent-to-treat analysis, a 50-mg DHEA substitution dose and placebo similarly improved fatigue. All of the MFI-20 subscales and the fatigue VAS improved from the baseline levels as a result of treatment (P < 0.001), but with negligible differences between these 2 treatments. The mean between-treatment difference was -0.1 for general fatigue (the primary outcome measure), 0.0 for physical fatigue, 0.0 for mental fatigue, 0.0 for reduced motivation, 0.3 for reduced activity, and 2.2 for the fatigue VAS. None of these differences was statistically significant. CONCLUSION: Similar to earlier results using pharmacologic doses, substitution treatment with 50 mg of DHEA in DHEA-deficient and severely tired primary SS patients does not help against fatigue better than placebo. This may relate to the prohormone nature of DHEA and its recently described defective intracrine tissue-specific conversion to active sex steroids in SS.
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