Influence of the tumor mass on the valine rate constants and on valine incorporation into proteins in an experimental brain tumor model

Quantitative autoradiography was used to estimate regional transfer coefficients for valine incorporation and the rate of valine (exogenous and total) incorporation into proteins in an implanted brain-tumor model (AA ascites tumor). Special attention was paid to the evaluation of the tumor mass influence on the transfer coefficients and the rate of incorporation. The size of the tumors used in this study ranged from 2 to 5 mm in diameter. Nine groups of two to three animals each were used to determine the transfer coefficient. The transfer coefficients for movement of the label between different compartments were significantly greater in the tumor than in the normal brain. There is no tumor mass effect on the transfer coefficients or the rate of valine incorporation into proteins in surrounding or remote brain structures. The ratio between specific radioactivities of the free valine in tissue and plasma was also measured. Results indicate that approximately the same fraction of the total valine is recycled in cortex as in the tumor tissue. The mean rates of exogenous valine incorporation into proteins (nmol g⁻¹ min⁻¹) is about one order of magnitude greater in the tumor than in the contralateral parietal cortex.