Regional glucose utilization and blood flow in experimental brain tumors studied by double tracer autoradiography

Coupling of regional glucose utilization (GLU) and blood flow (CBF) was examined in rats with implanted brain tumors (AA ascites tumor) by quantitative double tracer autoradiography using 18F-2-fluorodeoxyglucose and 14C-iodoantipyrine. Four to 13 days after implantation, the animals were injected with the two tracers to obtain autoradiograms from the same brain section before and after the decay of 18F. The autoradiograms were then analyzed by an image processor to obtain a metabolic coupling index (MCI = GLU/CBF). In the tumor, high GLU and low CBF were uncoupled to give a high MCI which implied anerobic glycolysis. In large tumors, the CBF was even lower. In the peri-tumoral region, GLU was reduced (especially in gray matter) and reduction was lowest around the larger tumors. CBF in the peri-tumoral region was also reduced, but this reduction became less as the distance from the tumor margin increased. These changes in the peri-tumoral region may be secondary to edema. The GLU and CBF of white matter was little influenced by the presence of tumors except for some reduction in these values in relation to the larger tumors. On a narrow margin of tumor and brain, corresponding to a zone of increased vascularity, CBF was moderately high. The MCI in the tumor was higher than in the cortex of the same as well as the opposite hemisphere. These findings indicate that the metabolism and blood flow of the tumor and surrounding brain are variable and directly related to tumor size.