Hepatic transport of gluconeogenic substrates during tumor growth in the rat

Hepatic gluconeogenic substrates (alanine, lactate, and glycerol) transport have been studied in liver plasma membrane vesicles from rats bearing the ascitic tumor Yoshida AH-130 hepatoma. Hepatic alanine uptake was increased in membrane vesicles from tumor-bearing animals as compared with those isolated from non-tumor-bearing controls. Although no changes were observed in relation with KM (2.19 and 2.10 mM for control and tumor groups, respectively), the presence of the tumor caused a clear increase in Vmax (3.07 and 5.04 nmol alanine/mg protein, respectively). The time course of lactate uptake showed no differences between the tumor-bearing animals and their corresponding controls. Both time course and kinetic experiments showed that liver glycerol uptake was due to passive diffusion and therefore cannot contribute to explain the enhanced utilization of this hepatic gluconeogenic substrate during tumor growth. The results suggest that hepatic alanine uptake may be an important factor accounting for its increased utilization for glucose synthesis in tumor-bearing rats.