IN VIVO UPTAKE OF [14C]LEUCINE BY SKELETAL MUSCLE RIBOSOMES AFTER INJURY IN RATS FED 2 LEVELS OF PROTEIN

1. After 14 days on a diet containing 5 or 25% casein male rats received a fracture of the left femur. Four hours before they were killed the injured and control rats were injected with [1-14C]leucine; the incorporation of radioactivity into an isolated fraction of skeletal muscle ribosomes was studied 6, 12, 24, 48, 72, 96 and 228 h after injury. 2. The incorporation of [14C]leucine into the ribosome fraction in right thigh muscles dropped to 40% of control values 72 h after fracture in well-nourished rats and after 96 h with diets containing 5 or 25%, casein. 3. The specific activity of the trichloroacetic acid-soluble fraction of muscle from injured rats was equal to or higher than that of the controls during the first 72 h but lower at 96 h. 4. These results suggest that a reduced incorporation of amino acids by ribosomes from the right thigh muscle occurred on day 3 after fracture in the group receiving 25% casein but not in the group receiving 5% casein. 5. Muscle RNA and DNA concentrations were not affected by the injury. 6. The relationship between these findings and the loss of muscle N after injury is discussed. © 1969, The Nutrition Society. All rights reserved.