Protein synthesis in compensatory hypertrophy of rat plantaris

Protein synthesis in rat plantaris muscle undergoing surgically induced hypertrophy was studied using a perfused hindquarter preparation. The tissue mass of the hypertrophied muscle increased 11, 33, 33, and 104% at 2, 5, 15, and 50 days postsurgery. Total tissue protein synthesis was unchanged during the early phase but was significantly elevated after 15 and 50 days of work overload. Myosin synthesis was also significantly elevated after 15 and 50 days of hypertrophic growth. Increases in muscle protein content (milligrams per muscle) for each protein fraction examined were temporally in step with the altered synthetic rates. The shift in muscle fibre-type profile from approximately 10% alkaline-labile fibres in the control muscle to about 25% alkaline-labile fibres in the hypertrophied muscle also followed a similar time course. These data suggest that during compensatory hypertrophy, enhanced protein synthesis may be the dominant mechanism for the massive accumulation of muscle protein. However, its contribution to muscle growth does not become evident until about 15 days after the initial growth stimulus.