Journal of Applied Physiology, Vol 64, Issue 5 1829-1836, Copyright © 1988 by American Physiological Society
Determination of rat brain buffering in vivo by 31P-NMR
S. Adler, V. Simplaceanu and C. Ho
Department of Medicine, University of Pittsburgh School of Medicine, Montefiore Hospital, Pennsylvania.
Buffering capacity of most tissues is composed of both rapid and slow
phases, the latter presumably due to active acid extrusion. To examine the
time course of brain buffering the brain pH of Sprague-Dawley rats was
measured using 31P-nuclear magnetic resonance. The effect on brain pH of
30- or 58-min exposures to 20% CO2 followed by 30- or 38-min recovery
periods, respectively, was studied. Brain pH reached its lowest value after
a 15-min exposure to elevated CO2, thereafter slowly and steadily
increasing. During recovery brain pH rose rapidly in the first 5 min
exceeding control brain pH by 0.08 pH units. Brain pH fell during the next
30 min despite increases in blood pH and decreases in blood CO2 tension.
Calculated intrinsic brain buffering rose steadily threefold during the
last 40 min of CO2 exposure and during the final 30 min of recovery. These
data show that in rat brain there is a temporally late buffering process,
most likely active acid extrusion, requiring greater than 30 min for full
activation and at least 30 min for discontinuation.
