SEVERE TRANSIENT HYPOGLYCEMIA CAUSES REVERSIBLE CHANGE IN THE APPARENT DIFFUSION-COEFFICIENT OF WATER

The aim of this study was to determine the effects of temporary severe hypoglycemia on the apparent diffusion coefficient (ADC) acquired by diffusion weighted MRI of brain water with the use of serial multislic e ADC mapping in rats. Severe hypoglycemia reduces the extracellular s pace volume, as does ischemia. Demonstrating a reduction of ADC with h ypoglycemia should increase our understanding of the mechanisms underl ying ADC changes in ischemia and other conditions. Methods Fasted rats were given regular insulin (15 IU/kg IP). Rats were subjected to 15 m inutes (n=5) and 50 minutes (n=5) of temporary severe hypoglycemia, ca using a transiently isoelectric electroencephalogram (EEG). ADC mappin g was per formed every 30 seconds beginning at the onset of isoelectri city for 8.5 minutes. ADC maps were also obtained later during the iso electric EEG period and 10, 20, 30, and 40 minutes after glucose infus ion. Control images were obtained from a separate group of animals suf fering cardiac arrest (n=5). Results Abnormal ADC values were not obse rved before the onset of cerebral isoelectricity, except for isolated areas in the cortex and periventricular regions. Cortical ADC values g lobally declined at the onset of EEG isoelectricity. The ADC decline s pread to subcortical regions within a few minutes. During the isoelect ric period, significant declines of ADC values (27% to 45%) occurred i n the entire brain. Glucose infusion normalized most of the ADC change s, even after a 50-minute period of isoelectricity. Conclusions ADC ma pping during hypoglycemia clearly demonstrates changes likely related to energy depletion. Most of these ADC declines were reversible. Hypog lycemia is a condition known to be associated with shrinkage of the ex tracellular space. These observations support the hypothesis that ADC reductions observed in ischemia are also related to shifts of water fr om the extracellular to the intracellular compartment.