Extracellular-intracellular distribution of glucose and lactate in the ratbrain assessed noninvasively by diffusion-weighted H-1 nuclear magnetic resonance spectroscopy in vivo

To determine the distribution of cerebral glucose and lactate between the i ntracellular and the extracellular space of the rat brain in vivo, the diff usion characteristic of glucose and lactate was compared with that of metab olites known to be mainly intracellular (N-acetylaspartate, choline, creati ne, glutamate, myo-inositol, and taurine) using a pulsed-field-gradient H-1 nuclear magnetic resonance technique. The detection of a glucose signal at large diffusion weighting provided direct experimental evidence of intrace llular glucose in the rat brain. At large diffusion weighting, the apparent diffusion coefficient (ADC) of glucose and lactate was similar to that of the intracellular metabolites such as N-acetylaspartate, creatine, and glut amate. At small diffusion weighting, the ADC of glucose and lactate was inc reased, which was explained by a decreased relative contribution of intrace llular glucose to the total signal. The calculated extracellular volume fra ction of glucose (0.19 +/- 0.05) and lactate (0.17 +/- 0.06) was consistent with a substantial fraction of glucose and lactate signals being intracell ular. The findings were direct in vivo evidence that the largest concentrat ion gradient of glucose is at the blood-brain barrier and that glucose is e venly distributed in the brain in vivo between the intracellular and extrac ellular space.