Amino acid profiles in tumor-bearing and pair-fed nontumor-bearing malnourished rats

To investigate the metabolic and organ changes accompanying growth of a malignant tumor, ten male Fisher 344 rats weighing 150 to 200 g were inoculated subcutaneously with 10(6) viable MCA sarcoma cells (tumor-bearing). Ten other rats (controls) were similarly inoculated with saline. Both groups were allowed food and water ad libitum. An additional ten rats (pair-fed) were inoculated with saline and fed the same mean daily food intake as the tumor-bearing rats. Thirty-five days after inoculation the rats were killed by exsanguination. Livers, spleens, and tumors were weighed, and amino acid profiles and biochemical parameters were measured. Liver and spleen weights in tumor-bearing rats were significantly greater than control rats (P less than 0.05 and P less than 0.01, respectively). Liver weight in pair-fed rats was significantly less than control rats (P less than 0.01), but spleen weight was greater (P less than 0.01). Amino acid profiles of tumor-bearing rats and pair-fed rats were different from each other and from those of control rats. Branched-chain amino acids were lowest in tumor-bearing rats and significantly different from control and pair-fed rats. Lysine was significantly higher (P less than 0.01) and arginine significantly lower (P less than 0.05) in tumor-bearing rats compared with control rats. These different plasma amino acid profiles and changes in serum biochemistry of cachectic tumor-bearing rats compared with malnourished pair-fed rats suggest specific tumor effects on host metabolism not mediated solely by anorexia.