Adaptations of Arginine's Intestinal-Renal Axis in Cachectic Tumor-Bearing Rats

Malignancies induce disposal of arginine, an important substrate for the immune system. To sustain immune function, the tumor-bearing host accelerates arginine's intestinal-renal axis by glutamine mobilization from skeletal muscle and this may promote cachexia. Glutamine supplementation stimulates argi-nine production in healthy subjects. Arginine's intestinal-renal axis and the effect of glutamine supplementation in cancer cach-exia have not been investigated. This study evaluated the long-term adaptations of the interorgan pathway for arginine production following the onset of cachexia and the metabolic effect of glutamine supplementation in the cachectic state. Fischer-344 rats were randomly divided into a tumor-bearing group (n = 12), control group (n = 7) and tumor-bearing group receiving a glutamine-enriched diet (n = 9). Amino acid fluxes and net fractional extractions across intestine, kidneys, and liver were studied. Compared to controls, the portal-drained viscera of tumor-bearing rats took up significantly more glutamine and released significantly less citrulline. Renal metabolism was unchanged in the cachectic tumor-bearing rats compared with controls. Glutamine supplementation had no effects on intestinal and renal adaptations. In conclusion, in the cachectic state, an increase in intestinal glutamine uptake is not accompanied by an increase in renal arginine production. The adaptations found in the cachectic, tumor-bearing rat do not depend on glutamine availability.