Morphological changes in skeletal muscle after transplantation

The morphological changes in subcutaneously implanted muscle homografts in mice were studied by light and electron microscopy 1–23 days after transplantation. The initial degenerative changes were identical in isografts and allografts and were essentially the same as those found in muscle explants in tissue culture and after various forms of muscle injury. Regenerative changes were prominent at the periphery of grafts by 48–72 hr before evidence of graft revascularization could be demonstrated by India ink perfusion. Active regeneration occurred in isografts and in allografts during the first week resulting in the formation of a new population of muscle fibres. Rejection subsequently occurred in allografts between days 7–14. Regeneration was retarded or completely inhibited by exposure of the donor animal to 1,500 rad of X-irradiation 1–2 hr prior to transplantation suggesting that regeneration is brought about by cells derived from the graft. Electron-microscopic observations in 48–72 hr grafts suggested that primitive mononucleated myogenic cells may form within degenerating muscle fibres by a process of myonuclear sequestration. Inactive satellite cells were present in the muscle from which grafts were taken in some donor animals but no definite conclusions could be reached as to the role of these cells in graft regeneration