Difference of 14C turnovers in brain and in transplanted glioma after intravenous injection of 14C-1-pyruvate into rats.

Carbon 14 from 14C-1-pyruvate injected intravenously into glioma-transplanted rats was incorporated into various compounds in the brain and in the tumor. In the brain the majority of activity was found in CO2 (60%), and minor activities were found in alanine, lactate (15%), glutamate, and aspartate, with decreasing order, 5 min after injection. In the tumor, at 5 min, the largest activity was in lactate (56%), and lower activities were found in CO2 (24%), alanine, glutamate, and aspartate. The total 14C concentration in the tumor was twice that in the brain at 5 min and 15 min. The result was in accordance with the prediction that in brain, where the mitochondrial function is active, 14C-1-pyruvate will be oxidized completely into 14CO2, and that in tumor, where the mitochondrial function is insufficient, 14C-1-pyruvate will be converted only into 14C-lactate and prevent further degradation. It may be assumed that this difference in the turnover of 14C of 14C-1-pyruvate between brain and tumor could constitute a basis for the 'hot' visualization of human brain tumor using cyclotron-produced 11C-1-pyruvate and positron-emission tomography.