The influence of preischemic hyperglycemia on acute changes in brain water ADC following focal ischemia in rats

Abstract

The effect of preischemic hyperglycemia on the acute decline of brain apparent diffusion coefficient of water (ADCw) following cerebral ischemia was studied in a rat model of middle cerebral artery occlusion (MCAO). ADCw was measured by NMR with a newly developed spin-echo line-scan protocol that provides for an ADCw calculation every 15 s at a spatial resolution of 3.4 μl/pixel. A remote controlled occluding device was used to initiate ischemia from outside the magnet, allowing for continuous monitoring of ADCw before, during and after MCAO. Preischemic hyperglycemia (25–30 mM) was achieved via i.v. infusion of 50% glucose. The decline in ADCw following ischemia was analyzed to obtain three-time constants: the time from onset of ischemia to initial significant ADCw decline below baseline level (i.e., 20% of maximal decline, T 0.20), the time to decline by 50% ( T 0.50), and the time to decline by 95% ( T 0.95). Mean (±S.D.) values for T 0.20, T 0.50, T 0.95 were: 39.6±7.2, 54.0±7.8, 105.0±15.0 s for the normoglycemic group ( n=7), and 49.2±33.0, 116.4±2.4, 351.0±189.0 s for the hyperglycemic group ( n=6), respectively. Hyperglycemia significantly prolongs T 0.50 and T 0.95 but does not affect T 0.20. The temporal profiles of ADCw decline following ischemia under normo- and hyperglycemia are distinctively different from the known time course of membrane depolarization under similar experimental conditions, suggesting that mechanisms other than membrane depolarization and cell swelling may contribute to changes in ADCw in cerebral ischemia.