Metabolic alterations in a noncachectic animal tumor system
The increased energy expended by the host to synthesize substrate, which is utilized by the tumor, is a potential cause of cancer cachexia. In vivo glucose and alanine kinetics were examined by tracer methodology in a sarcoma-bearing rat model. The effects of 3-mercaptopicolinic acid, a potent inhibitor of gluconeogenesis, was also examined on this model. Both tumor-bearing (TB) and nontumor bearing (NTB) animals were gaining weight prior to study and the tumors were relatively small. The TB animals had significantly lower plasma glucose and higher blood lactic acid levels compared with NTB animals. After inhibition of gluconeogenesis, the plasma glucose decreased and the blood lactate increased significantly more in TB than NTB animals. The glucose turnover rate was significantly greater in TB compared with NTB animals, as was the rate of glucose recycling and the rate of gluconeogenesis (alanine leads to glucose), both energy demanding processes. These results suggest that the tumor-bearing animal, even prior to significant cachexia, has an excess demand for energy, the provision of which may be a significant factor in malignant cachexia.