Compensatory adaptations of skeletal muscle composition to a long-term functional overload.

Compensatory hypertrophy of rat plantaris muscle was induced by ablating the synergistic gastrocnemius muscle. The sham-operated contralateral muscle served as a control. Within 5, 30 and 60 days postoperatively, the wet weight of the hypertrophied plantaris was 40, 64, and 109% greater, respectively, than the contralateral control. Two patterns of changing muscle composition emerged with compensatory hypertrophy: (1) an early (less than or equal to 5 days) increase in DNA content (+190%) which resulted in a sharp decline in the wet weight per nucleus ratio (-50%). This coincided with an increase in sarcoplasmic and stromal proteins and a fall in myofibrillar protein concentration. These changes were followed by (2) a secondary increase (30-60 days postoperatively) in the proportions of myofibrillar proteins with a corresponding decline in sarcoplasmic proteins.