title: Striking differences in glucose and lactate levels between brain extracellular fluid and plasma in conscious human subjects: effects of hyperglycemia and hypoglycemia.
abstract: Brain levels of glucose and lactate in the extracellular fluid (ECF), which reflects the environment to which neurons are exposed, have never been studied in humans under conditions of varying glycemia. The authors used intracerebral microdialysis in conscious human subjects undergoing electrophysiologic evaluation for medically intractable epilepsy and measured ECF levels of glucose and lactate under basal conditions and during a hyperglycemia-hypoglycemia clamp study. Only measurements from nonepileptogenic areas were included. Under basal conditions, the authors found the metabolic milieu in the brain to be strikingly different from that in the circulation. In contrast to plasma, lactate levels in brain ECF were threefold higher than glucose. Results from complementary studies in rats were consistent with the human data. During the hyperglycemia-hypoglycemia clamp study the relationship between plasma and brain ECF levels of glucose remained similar, but changes in brain ECF glucose lagged approximately 30 minutes behind changes in plasma. The data demonstrate that the brain is exposed to substantially lower levels of glucose and higher levels of lactate than those in plasma; moreover, the brain appears to be a site of significant anaerobic glycolysis, raising the possibility that glucose-derived lactate is an important fuel for the brain.
authors.affiliation: Department of Psychiatry, Yale University School of Medicine, New Haven, Connecticut 06519, USA.
authors.forename: Walid M
authors.initials: WM
authors.lastname: Abi-Saab
authors.forename: David G
authors.initials: DG
authors.lastname: Maggs
authors.forename: Tim
authors.initials: T
authors.lastname: Jones
authors.forename: Ralph
authors.initials: R
authors.lastname: Jacob
authors.forename: Vinod
authors.initials: V
authors.lastname: Srihari
authors.forename: James
authors.initials: J
authors.lastname: Thompson
authors.forename: David
authors.initials: D
authors.lastname: Kerr
authors.forename: Paola
authors.initials: P
authors.lastname: Leone
authors.forename: John H
authors.initials: JH
authors.lastname: Krystal
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Spencer
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: During
authors.forename: Robert S
authors.initials: RS
authors.lastname: Sherwin
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D003243:Consciousness; D004827:Epilepsy / Q000196:embryology*; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism*; D007003:Hypoglycemia / Q000378:metabolism*; D007700:Kinetics; D007773:Lactates / Q000097:blood / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D007773:Lactates; D005947:Glucose