Effects of Immobilization Atrophy on the Histochemical Characterization of Skeletal Muscle

¹ From the Division of Orthopedic Surgery, Departments of Surgery and Biochemistry, The University of Chicago, Chicago, Illinois

Experimental immobilization of one hind leg of puppies was produced in order to study biochemical changes in immobilization atrophy in the calf and thigh groups of muscles. The opposite leg or the sound one was used as the control leg. The puppies were arranged into three groups according to age and duration of immobilization. Group I: 12–14 weeks of age with 4–5 weeks of immobilization; group II: 13–17 weeks of age with 6–7 weeks of immobilization; group III: 17–20 weeks of age with 8–11 weeks of immobilization. An important finding in the original data was the progressive increase in total neutral fat content, depending upon the length of time of immobilization. The histochemical patterns for 1 kg of these muscles have been considered and control values compared with atrophic values. Irrespective of age or duration of immobilization there were increases in the extracellular compartment mass, which were the result mainly of an increased water content in this phase. The increased extracellular water was at the expense of the intracellular water. Simultaneous with the decrease in intracellular water content was a decrease in the solid mass of this phase to such an extent that the percentage of intracellular water in the atrophied muscle was the same as that in the sound muscle. Using the histochemical patterns for 1 kg of muscle, evidence has been presented to show that the internal structure of the muscle fibers did not change in immobilization atrophy. In all three groups of puppies, the percentage of muscle fiber water, as well as the potassium and magnesium concentrations, was the same whether expressed per kilogram of muscle fibers or per kilogram of muscle fiber water in all the calf and thigh groups of muscles from both the control and immobilized legs.