Metabolism of connective tissue in limb atrophy in the rabbit.

In previous experiments in adult rats (Slack, 1954, 1955), massive tissue atrophy was induced by denervation and femoral head dislocation of one hind limb. A study of the metabolism of total collagen, total sulphated polysaccharide, and mixed muscle protein indicated that disuse atrophy does not imply cessation of all protein or polysaccharide synthesis. After the onset of atrophy some synthesis of collagen appears to continue for at least 15 weeks. Synthesis of muscle protein continues for about 6 weeks and of sulphated polysaccharide for at least 2 weeks. The interesting finding was that at least some of the normal synthetic processes continue despite massive removal of muscle protein and connective tissue. These earlier experiments did not differentiate between connective tissue closely associated with the muscle mass, and connective tissue in the bones, joints, and associated tendon insertions. Furthermore, the rat experiments were open to objection because of the unusual operative technique required to achieve aseptic atrophy, and the fact that the bones of the rat appear to be capable of growth throughout much of the life of the animal. In view of the unexpected finding of continued connective tissue synthesis in the atrophying rat limb it was considered desirable to repeat the experiments in a larger animal. In the present experimental work, to be described, atrophy has been induced in one hind limb of rabbits by denervation. The metabolism of connective tissue collagen fractions and sulphated polysaccharide has been studied in two limb components: connective tissue associated with the muscle mass (soft tissue compartment), and that in bones, joints, and tendon insertions (skeletal compartment). Both the present work, and the previous experi-