METABOLIC CHARACTER OF HYPERTROPHIED RAT MUSCLE

Hypertrophy of the plantaris muscle was induced in male and female rats by myectomy of the synergistic gastrocnemius muscle. Selected histochemical and biochemical characteristics were studied to establish the time required to achieve a steady-state hypertrophy and to determine the metabolic character of chronically enlarged muscle. The plantaris muscle hypertrophied 38% by 2 days postmyectomy. Compensatory growth was completed by 30 days and, thereafter, maintained a relative enlargement of approximately 80%. Protein concentration (-17%), succinate dehydrogenase (DH) (-34%), and phosphofructokinase (-38%) activities were less for the first 2-5 days but returned to normal by 30 days. The percentage of slow-twitch fibers increased two to threefold by 30 days. During the relative steady-state hypertrophy, hexokinase, glutamate-pyruvate transaminase, malate DH, and aspartate transaminase activities were unchanged. Glycerol phosphate DH and 3-hydroxyacyl-CoA DH activities were increased; whereas, lactate DH was lower than normal. It was concluded that a sustained, relative steady-state hypertrophy for this model is established within 30 days and that the metabolic character of hypertrophied muscle undergoes only minor changes.