Summary
Changes in the brain lactate concentration in cerebral extracellular fluid (ECF) during
intravenous infusion of glucose and local administration of glucose were investigated
in adult, conscious, unrestrained rats, with a microdialysis probe in the posterior
hippocampus. The rats were infused intravenously with either 25% sucrose solution
or 25% glucose solution at a rate of 16.6 μl · min-1 · 100 g-1 for three hours. The blood glucose concentration reached 17.0±2.6 mM at the end of
the glucose infusion, and brain ECF glucose showed a parallel change with the blood
glucose concentration and increased to 2.37±0.30 mM. However, blood and brain ECF
glucose concentrations did not change in animals infused with the sucrose solution.
On the other hand, the blood lactate concentration in the glucose-infused group also
increased from 0.93±0.18 mM to 2.85±0.39 mM at the end of the glucose infusion, which
was significantly higher than that measured in the sucrose-infused group. The blood
lactate level in the glucose-infused group returned to the basal level by the end
of the experiment. Brain ECF lactate concentrations increased from 1.21±0.06 mM to
1.69±0.11 mM in glucose-infused animals, but did not change in the sucrose-infused
animals. The brain ECF lactate concentration showed a positive correlation with the
brain ECF glucose concentration in glucose-infused animals. Another group of rats
was administered glucose locally for 90 min after substitution of artificial cerebrospinal
fluid. As a result, the brain ECF lactate concentration increased significantly from
the control level during the glucose loading period, then gradually decreased by the
end of the experiment. The present study demonstrated that the brain lactate concentration
increased with the brain glucose concentration.
Key words
Hyperglycemia - Brain Glucose Metabolism - Lactate
