Early change in skeletal muscle protein synthesis after limb immobilization of rats.

The atrophy of skeletal muscle accruing from disuse, or limb immobilization, is caused by a decreased rate of protein synthesis and an increased rate of protein degradation. Currently, little information is available regarding the initial time of the decline in the rate of protein synthesis in skeletal muscle. The purpose of the present study was to determine, as precisely as possible, the time at which the protein synthesis rate first begins to decline in skeletal muscle, utilizing immobilized limbs of rats for a model. A constant-infusion technique employing [14C]tyrosine was used to estimate protein synthesis rates. During the first 6 h of immobilization, a significant decline of 37% in the fractional rate of protein synthesis from the control level of 5.7%/day was observed. These results suggest that very early changes are occurring in molecular events that regulate protein synthesis in disused or immobilized skeletal muscle.