Increased cerebral uptake of [[sup.18]F]fluoro-deoxyglucose but not [1-[sup.14]C]glucose early following traumatic brain injury in rats

Following experimental and clinical traumatic brain injury (TBI), the local cerebral metabolic rate of glucose ([lCMR.sub.Glc]) is commonly estimated using the 2-[18F]fluoro-2-deoxy-D-glucose (FDG) method. The adequate estimation of [lCMR.sub.Glc] using FDG requires a correction factor, the lumped constant (LC), to convert FDG net uptake into [lCMR.sub.Glc]. The LC, and thus [lCMR.sub.Glc] calculations, require a steady-state that may be disrupted following TBI. In the present report, we hypothesized that [1-[sup.14]C]glucose uptake would accurately reflect glucose dynamics early post-injury, and was compared to the regional uptake of FDG in 44 rats subjected to moderate (2.4-2.6 atm) lateral fluid percussion brain injury (FPI) or sham injury. Cortical energy state and adenylate (ATP, ADP, and AMP) levels were also measured. Early (7-42 min) after FPI, FDG uptake was increased in the ipsilateral cortex and hippocampus (p < 0.05). In contrast, no change in [1-14C]glucose uptake (7 and 17 min post-injury) or cortical adenylate content (42 min post-injury) was observed. At 12 h following FPI, the ipsilateral FDG and [1-14C]glucose uptake were decreased in the cortex and hippocampus, and the ipsilateral cortical ATP concentration was decreased in comparison to sham-injured controls (p < 0.05). Under the present experimental conditions, the rate of cerebral uptake of FDG and of [1-14C]glucose differed, and indicated that following TBI, regional changes in the LC may occur in the immediate, but not in the late, post-injury phase. These results should be considered when interpreting results obtained using FDG for the estimation of [lCMR.sub.Glc] early following experimental TBI. Key words: ATP; ADP; AMP; D-[1-[sup.14]C]-glucose; 2-[[sup.18]F]fluoro-2-deoxy-D-glucose; glucose uptake; lateral fluid percussion injury; lumped constant