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- Bergqvist, Peter B F
(författare)
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Tryptophan-related Neurotransmission in the Brain: Disturbances Associated with Experimental Hepatic Encephalopathy
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present study, L-tryptophan (TRP)-related disturbances in the brain in experimental hepatic encephalopathy (HE) were investigated. The endogenous NMDA-receptor agonist and L-TRP metabolite quinolinic acid (QUIN) has been suggested to be involved in the pathogenesis of HE. We were, however, unable to detect any increases in QUIN levels in rats subjected to a chronic portacaval shunt (PCS) either in plasma, brain tissue, or brain extracellular fluid. Furthermore, administration of ammonium acetate (NH4Ac) or L-TRP did not result in any difference in QUIN levels between PCS and sham-operated rats. The other main part of the actual study concerned investigations on the release of serotonin (5-HT) in the brain in HE. Despite a previously evidenced profound increase in brain metabolism of 5-HT in experimental HE, the neocortical release of 5-HT was found not to be changed in this situation. Challenges with L-TRP did not mainly affect the brain 5-HT release in either sham or PCS. NH4Ac administration caused a transient increase in brain 5-HT release of PCS rats during a time-period at which these rats were in a state of reversible coma. KCl provocation also resulted in clear elevations of the 5-HT output of PCS rats compared with matched controls. No difference in the 5-HT response to a d-fenfluramine (dFEN) administration was seen between sham and PCS rats. A clear difference in brain 5-HT release was, however, observed following p-chloroamphetamine (pCA) perfusion possibly indicating a larger extravesicular pool of 5-HT in PCS rats than in the brains of the sham-operated controls. In a final study, differences in pharmacodynamics as well as pharmacokinetics for the serotonin reuptake inhibitor citalopram were observed between PCS and sham. It is concluded that QUIN is not involved to any major extent in the pathogeneis of HE. The basal brain 5-HT release in not altered in experimental chronic PSE but an augmented neocortical 5-HT release compared with the normal in vivo situation is available under certain conditions. Based on these data a more restrictive use for e.g. potent novel 5-HT-acting drugs should be advocated in patients suffering from liver dysfunction and pending HE.
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- Engdahl, Göran, et al.
(författare)
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Statistical modeling of magnetic and magnetostrictive properties due to domain wall motion
- 1999
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 85:8, s. 5190-5192
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Tidskriftsartikel (refereegranskat)abstract
- Statistical mechanics is employed to derive magnetic and magnetostrictive bulk properties of soft magnetic materials dominated by domain wall motion. The material is divided into an ensemble of volumes with uniform magnetization, each one much smaller than a typical domain but much larger than one atom. The energy for such a volume element is assumed to consist of an internal energy: the interaction with the external magnetic field and a mean field interaction with the surrounding medium. The volume fractions of discrete mesoscopic magnetizations in the medium are derived from Boltzmann statistics. The bulk magnetization is the weighted average of the mesoscopic values. Magnetostriction is treated in a similar way. Calculations are compared with two-dimensional measurements on grain-oriented silicon #x2013;iron. #xa9; 1999 American Institute of Physics.
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- Hansen, F, et al.
(författare)
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Accuracy of duplex sonography before carotid endarterectomy--a comparison with angiography
- 1996
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Ingår i: European Journal of Vascular and Endovascular Surgery. - 1532-2165. ; 12:3, s. 331-336
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: The aim of this prospective study was to contribute to the evaluation of the reliability of Duplex sonography (DS) before carotid endarterectomy (CEA). DESIGN: The study was performed prospectively in a university hospital setting. METHODS: Eighty-one consecutive patients aged 49-83 years were examined with DS and carotid angiography (CAG) before CEA. The results of the DS were judged as either confident, or CAG was assessed to be necessary preoperatively. The results from the DS and the CAG were then compared. RESULTS: DS was judged as confident in 148 of the 162 arteries examined. In none of these 148 arteries did CAG change patient management in any way, and the agreement between DS and CAG was good. In the remaining 14 arteries CAG was judged necessary, in 11 arteries because DS assessed the internal carotid artery (ICA) as occluded, which was confirmed by CAG in 10 arteries. In three arteries the reason was poor quality of the DS, however these three arteries were correctly assessed as severely diseased. CONCLUSIONS: This study confirms that DS alone is sufficient in the preoperative evaluation before CEA, provided that CAG is performed whenever DS shows occlusion of the ICA, or when the quality of the DS is poor.
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