Regeneration pattern of cardiac and skeletal muscle after transplantation into a skeletal muscle bed in rats

Background: The ability of skeletal muscle to regenerate after injury is well established. In contrast, cardiac muscle is incapable of regeneration and recovery after injury. The aim of the present study was to evaluate and compare the regeneration pattern of cardiac and skeletal muscle after transplantation into a skeletal muscle bed in rats. Methods: The following group of transplants were performed at the site prepared by removing the host extensor digitorum longus (EDL) muscle. The first group consisted of cardiac muscle transplanted as one piece or after mincing into 1‐mm pieces. The second group included cotransplants of cardiac and skeletal muscle minces that were intermixed. Entire EDL muscle or minced EDL muscle were also transplanted for comparison. Rats were sacrificed 3–30 days after transplantation for morphological analysis. Results: The results demonstrated that skeletal muscle transplants underwent rapid regeneration, and by 30 days the entire muscle was filled with regenerated myofibers. In transplants of cardiac muscle significant inflammation, myocardial degeneration and necrosis were observed. In spite of the necrosis and fibrosis, the presence of a few regenerated myotubes in the outer region was observed. In cardiac and skeletal muscle cotransplants, the inflammation was restricted to cardiac tissue; however, by 30 days the entire contransplant was filled with regenerated myotubes and myofibers. Conclusions: These results show that skeletal muscle is capable of growth, regeneration, and integration with the cardiac muscle after cotransplantation. Combination of skeletal and cardiac muscle may prove useful in defining the cellular processes necessary for enhancing cardiac repair after injury. © 1995 Wiley‐Liss, Inc.