title: Regional differences in osmotic behavior in brain during acute hyponatremia: an in vivo MRI-study of brain and skeletal muscle in pigs.
abstract: Brain edema is suggested to be the principal mechanism underlying the symptoms in acute hyponatremia. Identification of the mechanisms responsible for global and regional cerebral water homeostasis during hyponatremia is, therefore, of utmost importance. To examine the osmotic behavior of different brain regions and muscles, in vivo-determined water content (WC) was related to plasma sodium concentration ([Na(+)]) and brain/muscle electrolyte content. Acute hyponatremia was induced with desmopressin acetate and infusion of a 2.5% glucose solution in anesthetized pigs. WC in different brain regions and skeletal muscle was estimated in vivo from T(1) maps determined by magnetic resonance imaging (MRI). WC, expressed in gram water per 100 g dry weight, increased significantly in slices of the whole brain [342(SD = 14) to 363(SD = 21)] (6%), thalamus [277(SD = 13) to 311(SD = 24)] (12%) and white matter [219(SD = 7) to 225(SD = 5)] (3%). However, the WC increase in the whole brain and white mater WC was less than expected from perfect osmotic behavior, whereas in the thalamus, the water increase was as expected. Brain sodium content was significantly reduced. Muscle WC changed passively with plasma [Na(+)]. WC determined with deuterium dilution and tissue lyophilzation correlated well with MRI-determined WC. In conclusion, acute hyponatremia induces brain and muscle edema. In the brain as a whole and in the thalamus, regulatory volume decrease (RVD) is unlikely to occur. However, RVD may, in part, explain the observed lower WC in white matter. This may play a potential role in osmotic demyelination.
authors.affiliation: Department of Anesthesiology, Aarhus University Hospital, Aarhus Sygehus NBG, Aarhus, Denmark. christian.overgaard.steensen@ki.au.dk
authors.forename: Christian
authors.initials: C
authors.lastname: Overgaard-Steensen
authors.forename: Hans
authors.initials: H
authors.lastname: Stødkilde-Jørgensen
authors.forename: Anders
authors.initials: A
authors.lastname: Larsson
authors.forename: Martin
authors.initials: M
authors.lastname: Broch-Lips
authors.forename: Else
authors.initials: E
authors.lastname: Tønnesen
authors.forename: Jørgen
authors.initials: J
authors.lastname: Frøkiaer
authors.forename: Troels
authors.initials: T
authors.lastname: Ring
mesh_terms: D000208:Acute Disease; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D001929:Brain Edema / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D017666:Deuterium Oxide; D004195:Disease Models, Animal; D045604:Extracellular Fluid / Q000378:metabolism*; D005260:Female; D007010:Hyponatremia / Q000150:complications / Q000378:metabolism* / Q000473:pathology; D008279:Magnetic Resonance Imaging; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009994:Osmolar Concentration; D009995:Osmosis; D011188:Potassium / Q000097:blood; D011865:Radioisotope Dilution Technique; D015203:Reproducibility of Results; D012964:Sodium / Q000097:blood*; D013552:Swine; D013997:Time Factors
chemical_list: D012964:Sodium; D017666:Deuterium Oxide; D011188:Potassium