Flow thresholds for cerebral energy disturbance and Na+ pump failure as studied by in vivo 31P and 23Na nuclear magnetic resonance spectroscopy.
The relationships among CBF, cerebral energy metabolism, Na+ pump activity, and electrocorticograms (ECoG) following graded hypotension were studied in 48 gerbils. Energy metabolism and Na+ pump activity were estimated by in vivo 31P and 23Na nuclear magnetic resonance (NMR) spectroscopy, and CBF was determined by [14C]iodoantipyrine methods at the end of the experiments. The CBF measured in normotensive animals was 0.51 +/- 0.07 ml/g brain/min. Following graded hypotension, no 31P spectral change was observed until CBF fell to 0.21-0.27 ml/g brain/min, at which level the intracellular pH began to decrease in association with ECoG voltage reduction. At a CBF level of 0.18-0.23 ml/g brain/min, phosphocreatine (PCr) began to decrease in association with inorganic phosphate (Pi) elevation. At this level, ECoG became isoelectric, although no adenosine triphosphate (ATP) change yet resulted. At a flow level of 0.12-0.14 ml/g brain/min, ATP began to decrease gradually. At 0.04-0.05 ml/g brain/min, PCr and ATP virtually disappeared, and the 23Na signal intensity suddenly changed. The present study demonstrated flow thresholds for the development of tissue acidosis, PCr-Pi changes, and ATP reduction. It appears that functional suppression occurs prior to ATP changes, whereas Na+ pump failure results after ATP depletion.
D000818:Animals; D001769:Blood; D001794:Blood Pressure; D001921:Brain / Q000503:physiopathology*; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation; D004569:Electroencephalography; D004734:Energy Metabolism; D005849:Gerbillinae; D006863:Hydrogen-Ion Concentration; D007022:Hypotension / Q000503:physiopathology*; D007473:Ion Channels / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D010100:Oxygen / Q000097:blood; D012964:Sodium / Q000378:metabolism*
D007473:Ion Channels; D002245:Carbon Dioxide; D012964:Sodium; D010100:Oxygen