Abstract
Skeletal muscle hypertrophy consists of both enlargement of muscle fibers and an increase in the number of muscle cells. Recently, it was shown that muscle cell proliferation is induced by some growth factors like FGF and IGF-1. New muscle fibers are formed by proliferation and fusion of myogenic cells. Since the number of satellite cells has been shown to decrease with aging, the existence of myogenic cells other than satellite cells is suggested. The origin of myogenic cells, detected by their positivity for myogenin, which is a transcription factor peculiar to muscular cells, was examined in this study. Histochemical examination revealed, myogenin-positive cells in blood vessels and periphery of muscular tissue and suggested possibility of myogenic cells being carried to muscular tissue through blood. In addition, albumin positive cells, which specifically appeared in an identical distribution in hypertrophied muscle, were also observed. It was suggested from the findings in this study that the hepatic stem cells(HSC) may function as myogenic cells. Furthermore, we examined the transplantation of HSCin an overloaded muscle by tenotomy. After one week, transplanted HSC nuclei were observed in the hypertrophied muscle. These results suggest that the liver may be the source of the myogenic cells in hypertrophied and regenerating muscle following exercise, and that supplementation hepatocyte might have an important role in the adaptation of muscle tissue architecture in response to exercise. [Jpn J Physiol 54 Suppl:S55 (2004)]
