AJP - Endocrinology and Metabolism, Vol 253, Issue 4 E418-E427, Copyright © 1987 by American Physiological Society
Effect of superfused insulin on cerebral cortical glucose utilization in awake goats
D. A. Pelligrino, D. J. Miletich and R. F. Albrecht
Department of Anesthesiology, Michael Reese Hospital and Medical Center, Chicago, Illinois 60616.
The effect on cortical cerebral glucose utilization (CMRglu) of
intracerebral insulin administration in awake goats was studied. The
insulin was superfused in a mock cerebrospinal fluid (CSF) solution
employing chronically implanted cranial windows. Two windows were implanted
bilaterally: one window over an equivalent portion of each parietal cortex.
With one window used to deliver insulin/CSF and the other used to
simultaneously deliver CSF alone (control), changes in CMRglu were assessed
using a modification of a sequential 2-[3H]- then 2-[14C]deoxy-D-glucose
(2DG) technique originally described by Altenau and Agranoff (Brain Res.
153: 375-381, 1978). Initial experiments employing 125I-insulin
demonstrated that the superfusion procedure increased insulin levels only
in the outer 1 mm of cortical tissue exposed to insulin containing
perfusate. Additional preliminary evaluations, using conditions known to
alter CMRglu, generally established that present methods were adequate to
induce and detect CMRglu changes. However, it was also shown experimentally
and using a mathematical model that 2-[3H]DG test/control tissue ratios
could be influenced by subsequent changes in CMRglu and the
dephosphorylation rate. Thus 3H ratios could not be used to establish
preexperimental test/control CMRglu relationships as the originally devised
model assumed but could be employed to indicate changes in
dephosphorylation. The mathematical model allowed for improved estimates of
CMRglu changes from 2-[14C]DG/2-[3H]DG test over control tissue ratios.
Even with these corrections, insulin was estimated to cause no more than an
8-15% increase in cortical CMRglu. A very limited role for insulin, at
least in cerebral cortical metabolic regulation, is thus indicated.
