ALANINE METABOLISM IN RATS BEARING THE YOSHIDA AH-130 ASCITES HEPATOMA

Rats bearing the Yoshida AH-130 ascites hepatoma, a cachectic rat tumo ur, showed signs of important muscle wasting with reduced muscle weigh ts. This phenomenon was associated with a decreased rate of in vivo al anine oxidation as measured by the production of (CO2)-C-14 from [U-C- 14]alanine intragastrically administered. it was later found that the decreased amino acid oxidation was associated with a reduced uptake in skeletal muscle as measured in incubated soleus muscles, thus suggest ing that the decreased in vivo oxidation is basically due to a reduced oxidation of the amino acid in skeletal muscle. The decrease in alani ne oxidation in the tumour-bearing animals was also associated with hi gher circulating alanine concentrations in their blood. In addition, t umour-bearing rats presented a lower (26%) protein synthetic rate in s keletal muscle, as measured by the incorporation of [C-14]phenylalanin e into muscle protein, The addition of insulin to the incubation mediu m abolished the tower rate of protein synthesis, thus suggesting a gre ater response to this hormone by the muscle of tumour-bearing rats. In conjunction with a reduced protein synthesis, tumour-bearing rats sho wed a clearly enhanced rate of protein degradation in isolated skeleta l muscles. The results presented confirm previous observations suggest ing that the skeletal muscle of tumour bearing animals is in a profoun d negative nitrogen balance which partially accounts for the wasting o bserved in the tissue. in addition, the present study allows us to con clude that, in spite of the increased alanine utilization for both glu coneogenesis and tumour growth, the oxidation of alanine by the whole animal is decreased in the tumour-bearing rats. This seems to be assoc iated with a decreased ability of skeletal muscle to handle this amino acid.