title: Extracellular potassium activity and cerebral blood flow during moderate hypoglycemia in anesthetized dogs.
abstract: Moderate hypoglycemia (MH) may be associated with blunting of cerebral hypocapnic vasoconstriction. Coincident with this change, electroencephalogram (EEG) flattening occurs. Previous reports show that brain extracellular potassium activity ([K+]o) increases in association with the onset of isoelectricity during severe hypoglycemia and that K+ increases cause pial vessel vasodilation. Using a model of MH, we tested the hypothesis that increases in [K+]o (approximately 15 mM) correlate with blunting of cerebral hypocapnic vasoconstriction. Cerebral blood flow (CBF), [K+]o, and EEG were measured during normocapnia [arterial Pco2 (Paco2) = 35 Torr)] and hypocapnia (PaCO2 = 15 Torr) in MH (< 2 mM) and normoglycemic dogs. During MH, increases in [K+]o occurred in association with EEG flattening (from 4.2 +/- 0.5 to 13.8 +/- 3.8 mM). During normoglycemia and MH without [K+]o elevations, hypocapnic vasoconstriction occurred. [K+]o elevations with MH were associated with increased CBF and decreased vascular resistance (146 +/- 5 and 42 +/- 2% of control, respectively) during normocapnia, and blunting of cerebral hypocapnic vasoconstriction (93 +/- 16% normocapnic control) when [K+]o increased during hypocapnia. This study shows that increases in [K+]o during MH are necessary for both normocapnic increases in CBF and blunting of cerebral hypocapnic vasoconstriction. Increases in [K+]o may represent a mechanism for decreases in cerebral vascular resistance during MH.
authors.affiliation: Department of Anesthesiology, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
authors.forename: F E
authors.initials: FE
authors.lastname: Sieber
authors.forename: D A
authors.initials: DA
authors.lastname: Wilson
authors.forename: D F
authors.initials: DF
authors.lastname: Hanley
authors.forename: R J
authors.initials: RJ
authors.lastname: Traystman
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002560:Cerebrovascular Circulation; D004285:Dogs; D005110:Extracellular Space / Q000378:metabolism*; D007003:Hypoglycemia / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D010101:Oxygen Consumption; D011188:Potassium / Q000378:metabolism*; D014655:Vascular Resistance
chemical_list: D011188:Potassium