MUSCLE AND LIVER PROTEIN-SYNTHESIS ADAPT EFFICIENTLY TO FOOD-DEPRIVATION AND REFEEDING IN 12-MONTH-OLD RATS

Our aim was to analyze mechanisms involved in the adaptation of protei n metabolism to food deprivation and refeeding in adult rats. Twelve-m onth-old rats, which had been food-deprived for 113 h and refed for 6 h, were injected subcutaneously with a flooding dose of valine (with 5 0% [1(13)C]-L-valine) to measure in vivo protein synthesis in tibialis anterior, soleus and liver. Protein and RNA contents were also measur ed. In both muscles, protein mass was maintained during food deprivati on. Due to a drop in protein synthetic capacity (Cs), total and myofib rillar protein synthesis rates were reduced in food-deprived rats and were not stimulated by a 6-h refeeding. In contrast, protein levels we re maintained lower than RNA levels in liver during food deprivation, and Cs was higher than in fed rats. Protein synthesis rates and riboso mal efficiency were reduced in food-deprived rats. Due to maintenance of protein synthetic capacity, there was a rapid stimulation of liver protein synthesis with refeeding, which induced a significant rise in protein mass (also related to an inhibition of protein degradation). I n conclusion, coordinated responses of liver and muscles allowed a spa ring of muscle proteins during food deprivation and a rapid recovery o f liver proteins during refeeding. Control of ribosome quantity could play a critical role in these adaptations in tissue protein synthesis in adult rats.