Protein synthesis rates (flooding dose with 13C-valine) and accretion were assessed in individual tissues of fasted or fed rats (n = 32) after a 2-wk adaptation to a normal- or high-protein (HP) diet.
In livers of HP rats, a strong inhibition of protein synthesis rates (−34 % ) occurred in the fasted and fed states, whereas a higher protein content (+10 % ) was observed. In the kidneys, a slight inhibition of synthesis rates after the HP diet was also observed but remained without effect on kidney protein pool size. Stomach and skin protein synthesis rates were significantly increased under HP conditions, whereas protein anabolism in skeletal muscle remained insensitive to the dietary protein level. This was also true for specific muscle protein fractions: myosin, mitochondrial, or sarcoplasmic protein synthesis rates were influenced by neither the dietary protein level nor the nutritional status.
Modulation of protein kinetics and accretion by the HP diet is tissue-specific and the liver plays a critical role in such adaptations in a unique situation associating an inhibition of protein synthesis and protein pool expansion. The mechanisms underlying these changes and their physiologic incidence remain to be elucidated.