| Abstract: | Reevaluation of lumped and rate constants is necessary when Sokoloff's 2-deoxyglucose (DG) method is used to measure glucose utilization in pathological tissue. We describe here a modification of Sokoloff's lumped constant measurement that permits simultaneous estimation of both lumped and rate constants from a single animal experiment. A subcutaneous tumor model (AA ascites tumor) was used for measurement of these constants with a procedure similar to Sokoloff's that kept the plasma tracer concentration constant. Measured constants were as follows: lumped constant, 0.654 +/- 0.081; k1, 0.196 +/- 0.038 min-1; k2, 0.262 +/- 0.067 min-1; k3, 0.117 +/- 0.044 min-1. These constants were used to quantify glucose utilization in the implanted brain tumor. To test the validity of this method, we compared a fraction of the free DG pool calculated using the tumor constants with a fraction measured directly by chromatographic analysis of tissue samples from both subcutaneous tumor and implanted brain tumor. The values derived by chemical analysis agreed well with those predicted by the calculations. The value of k4 varied from 0.0031 +/- 0.0018 min-1 for the tumor tissue to 0.0214 +/- 0.0024 min-1 for tumors with a large necrotic center. This method would be especially useful when applied to xenograft human gliomas in nude mice for quantification of glucose utilization in human gliomas by means of positron emission tomography. |
