The presence of the connective tissue components fibronectin and the different types of collagen was demonstrated by histological and immunohistological methods in the granulation and scar tissue of a healing injury in rat muscle. The effects of physical activity on granulation tissue production, scar formation and muscle regeneration at various stages of healing were studied. It was shown that immobilisation after injury accelerates granulation tissue production, but if continued too long, leads to contraction of the scar and to poor structural organisation of the components of regenerating muscle and scar tissue. However, a certain period of immobilisation, about five days for rat muscle, is required to allow newly-formed granulation tissue to cover the injured area and to have sufficient tensile strength to withstand subsequent mobilisation. This mobilisation, at the correct interval, seems essential for the quicker resorption of scar tissue and the better structural organisation of the muscle.
The three isomorphic forms of collagen present in muscle have been located by indirect immunofluorescence using collagen type specific antibodies. Type I collagen was located in the epimysium and perimysium, type I11 primarily in the perimysium as fine lace-like fibres, and type V virtually confined to the endomysium. Increased proportions of type I11 collagen appeared to be present in the perimysium of the tougher muscles M. carpi radialis, and M . sternomandibularis compared to M . semitendinosus and M. longissimus dorsi. This increased proportion of type 111 was confirmed by analysis of the cyanogen bromide peptides. The relationship of the increased proportion of type I11 collagen to increased toughness, if any, remains to be elucidated.
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