Deoxyglucose Lumped Constant Estimated in a Transplanted Rat Astrocytic Glioma by the Hexose Utilization Index

The lumped constant (LC) for calculating the regional glucose (glc) metabolic rate by the deoxyglucose (DG) method was estimated in a transplanted rat glioma and normal rat brain. First, the hexose utilization index (HUI) was measured at 1.5, 3.0, and 4.5 min in right hemisphere glioma implants and uninvolved contralateral hemisphere following bolus intravenous injections of [³H]DG and [¹⁴C]glucose. At these times, the glioma HUI values were 0.639, 0.732, and 0.712, respectively, and the coordinate left hemisphere values were 0.432, 0.449, and 0.418. Second, the volumes of distribution of DG and glucose were determined to be 0.436 and 0.235 in glioma implants and 0.402 and 0.237 in left hemisphere, respectively. Third, following simultaneous intracarotid injections of [³H]DG and [¹⁴C]glucose, the ratio K*₁/K₁ was 1.1 in glioma grafts and 1.3 in left hemisphere. With these values for HUI, volume of distribution, and K₁ ratio, the LC in this rat glioma was estimated to be 2.1 times higher than the left hemisphere LC (p < 0.02). These results suggest that measurement of brain tumor CMR_glc using a normal brain LC may significantly overestimate the true tumor CMR_glc.