AJP - Endocrinology and Metabolism, Vol 254, Issue 4 E443-E448, Copyright © 1988 by American Physiological Society
Measuring brain glucose phosphorylation with labeled glucose
H. E. Brondsted and A. Gjedde
Department of General Physiology and Biophysics, Panum Institute, University of Copenhagen, Denmark.
This study tested whether glucose labeled at the C-6 position generates
metabolites that leave brain so rapidly that C-6-labeled glucose cannot be
used to measure brain glucose phosphorylation (CMRGlc). In
pentobarbital-anesthetized rats, the parietal cortex uptake of [14C]glucose
labeled in the C-6 position was followed for times ranging from 10 s to 60
min. We subtracted the observed radioactivity from the radioactivity
expected with no loss of labeled metabolites from brain by extrapolation of
glucose uptake in an initial period when loss was negligible. The observed
radioactivity was a monoexponentially declining function of the total
radioactivity expected in the absence of metabolite loss. The constant of
decline was 0.0077.min-1 for parietal cortex. Metabolites were lost from
the beginning of the experiment. However, with correction for the loss of
labeled metabolites, it was possible to determine an average CMRGlc between
4 and 60 min of circulation of 64 +/- 4 (SE; n = 49) mumol.hg-1.min-1.
