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 rumor-bearing animals as compared with those iso lated from nontumor-bearing controls. Although no changes were observed in relation with KM (2.19 and 2.10 mM for control and tumor groups, respective ly), the presence of the tumor caused a clear increase in V-max (3.07 and 5 .04 nmol alanine/mg protein, respectively). The time course of lactate upta ke showed no differences between the tumor-bearing animals and their corres ponding controls. Both rime course and kinetic experiments showed that live r glycerol uptake was due to passive diffusion and therefore cannot contrib ute to explain the enhanced utilization of this hepatic gluconeogenic subst rate during tumor growth. The results suggest that hepatic alanine uptake m ay be an important factor accounting for its increased utilization for gluc ose synthesis in rumor-bearing rats.