Critical oxygen tension in rat brain: a combined (31)P-NMR and EPR oximetry study.
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.
Rolett
E L
EL
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
Azzawi
A
A
Liu
K J
KJ
Yongbi
M N
MN
Swartz
H M
HM
Dunn
J F
JF
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
D004343:Drug Implants; D007211:Indoles; D009942:Organometallic Compounds; D013113:Spin Labels; C081756:lithium phthalocyanine; D010100:Oxygen