title: Critical oxygen tension in rat brain: a combined (31)P-NMR and EPR oximetry study.
abstract: The relationship between cerebral interstitial oxygen tension (Pt(O(2))) and cellular energetics was investigated in mechanically ventilated, anesthetized rats during progressive acute hypoxia to determine whether there is a "critical" brain Pt(O(2)) for maintaining steady-state aerobic metabolism. Cerebral Pt(O(2)), measured by electron paramagnetic resonance oximetry, decreased proportionately to inspired oxygen fraction. (31)P-nuclear magnetic resonance measurements revealed no changes in P(i), phosphocreatine (PCr)/P(i) ratio, or intracellular pH when arterial blood oxygen tension (Pa(O(2))) was reduced from 145.1 +/- 11.7 to 56.5 +/- 4.4 mmHg (means +/- SE). Intracellular acidosis, a sharp rise in P(i), and a decline in the PCr/P(i) ratio developed when Pa(O(2)) was reduced further to 40.7 +/- 2.3 mmHg. The corresponding Pt(O(2)) values were 15.1 +/- 1.8, 8.8 +/- 0.4, and 6.8 +/- 0.3 mmHg. We conclude that over a range of decreasing oxygen tensions, cerebral oxidative metabolism is not sensitive to oxygen concentration. Oxygen becomes a regulatory substrate, however, when Pt(O(2)) is decreased to a critical level.
authors.affiliation: Department of Medicine, Nuclear Magnetic Resonance and Electron Paramagnetic Resonance Research Centers, Dartmouth-Hitchcock Medical Center, Hanover, New Hampshire 03755, USA. ellis.rolett@dartmouth.edu
authors.forename: E L
authors.initials: EL
authors.lastname: Rolett
authors.forename: A
authors.initials: A
authors.lastname: Azzawi
authors.forename: K J
authors.initials: KJ
authors.lastname: Liu
authors.forename: M N
authors.initials: MN
authors.lastname: Yongbi
authors.forename: H M
authors.initials: HM
authors.lastname: Swartz
authors.forename: J F
authors.initials: JF
authors.lastname: Dunn
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure; D001921:Brain / Q000378:metabolism*; D004343:Drug Implants; D004578:Electron Spin Resonance Spectroscopy; D004734:Energy Metabolism / Q000502:physiology; D006339:Heart Rate; D006863:Hydrogen-Ion Concentration; D002534:Hypoxia, Brain / Q000175:diagnosis / Q000378:metabolism; D007211:Indoles / Q000008:administration & dosage; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009942:Organometallic Compounds / Q000008:administration & dosage; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013113:Spin Labels
chemical_list: D004343:Drug Implants; D007211:Indoles; D009942:Organometallic Compounds; D013113:Spin Labels; C081756:lithium phthalocyanine; D010100:Oxygen