Endurance exercise modifies cachexia of tumor growth in rats

Food intakes, body composition, skeletal muscle mass, muscle protein synthesis, and myofibrillar protein degradation were studied in normal, food-restricted (FR), and Walker 256 tumor-bearing (TB) male Sprague-Dawley rats which were exercised (E) or maintained in a sedentary state. Exercise was enforced 3 times per wk for 100 min X session-1 at 20 m X min-1 on a 13% incline for 7 wk. Tumors were transplanted 3 wk after beginning the exercise program and were allowed to grow for 29 d. Food restriction was initiated during the last 2 wk of tumor growth. Food intakes and body lipid stores were reduced in all E groups, whereas body nitrogen was reduced only in the TBS animals. All E animals had significantly higher gastrocnemius muscle/body weight ratios than their sedentary counterparts, with the greatest ratio noted for the TBE animals. Muscle protein synthesis, measured by incorporation of [3H]tyrosine into gastrocnemius muscle, was significantly depressed in both FR and TB animals. Muscle protein breakdown, estimated by urinary 3-methylhistidine excretion, was significantly elevated in TB animals and slightly increased in FR animals. The results suggest that tumor presence significantly alters protein turnover to a greater extent than elicited by food restriction alone. Additionally, although exercise may have initially protected the animal by retarding tumor growth and muscle mass depletion, in the end, the energy costs of exercise accelerated the catabolic state.