THE INFLUENCE OF PREISCHEMIC HYPERGLYCEMIA ON ACUTE CHANGES IN THE APPARENT DIFFUSION-COEFFICIENT OF BRAIN WATER FOLLOWING GLOBAL-ISCHEMIA IN RATS

We report the effect of increased plasma glucose levels on changes in the apparent diffusion coefficient of brain water (ADCw) during the fi rst few minutes of global ischemia in rats. Brain ADCw values were acq uired every 15 s using a diffusion-weighted line-scan MR pulse sequenc e. Preischemic hyperglycemia was achieved by infusion of 50% dextrose (i.v.) prior to KCl-induced cardiac arrest global ischemia. Analysis b ased on single voxels (3.4 mu l) in brain demonstrated significant dif ferences in the time course of ADCw decline between normoglycemic (n = 8) and hyperglycemic (n = 6) groups. Mean data from the hyperglycemic group indicated a biphasic decline of ADCw that was characterized by an initial rapid drop followed by a plateau of approximately 1 min bef ore gradually declining and leveling off to its minimum value. In the normoglycemic group, ADCw declined to the same value as in the hypergl ycemic group, but without a notable plateau. In the cerebral cortex, t he times to maximal and half maximal ADCw drop following global ischem ia in the hyperglycemic group were 3.96 and 2.26 min respectively. Cor responding time intervals for the normoglycemic group were 1.86 and 1. 14 min, respectively. The time course for changes in ADCw demonstrated here is significantly different than that for anoxic depolarization r eported under similar experimental conditions and suggests that events other than the complete loss of membrane ionic homeostasis and subseq uent cell swelling may be involved in the initial decline of ADCw in g lobal cerebral ischemia.