Elevated energy expenditure in hepatocytes from tumor-bearing rats

Mechanisms for the development of cancer cachexia are not well defined. Oxygen consumption and the capacity of the host liver to metabolize lactate were studied in isolated hepatocytes from sarcoma-bearing rats (TIH) and pair-fed controls (CH). Basal oxygen consumption (without exogenous substrate) is significantly increased by 65% in the TIH as compared to the CH. The addition of a physiologic concentration of lactate stimulated oxygen consumption over the already stimulated basal state by 13% in the TIH compared to 5% in the CH. When the hepatocytes are incubated with 1.5 mM of [U-14C]lactate, glucose production, lactate oxidation, and entry of lactate carbons into nonsecretory protein are significantly increased in the TIH. Associated with this stimulation is a significant decrease in lactate incorporation into glycogen and lipid in the TIH. This study suggests that the tumor-influenced liver utilizes lactate at an increased rate and its intermediary metabolism is directed toward energy utilization rather than energy storage. The enhanced metabolic processes in the tumor-influenced liver are associated with an increased oxygen consumption which may be a contributory factor to the negative energy balance, a characteristic of cancer cachexia.