GROWTH HORMONES/FACTORS & MUSCLE CELLS
Skeletal muscle contains cells that are critical for growth and regeneration of the muscle; this is of particular importance after injury. Growth hormones and growth factors are studied for their effects on skeletal muscle satellite cells. Different studies demonstrate mediated aspects and combined effects. Findings show that GH and IGF-I affect satellite cell proliferation and FGF signals are mediated through several alternatively spliced variants of FGFR1.
Skeletal muscle contains myogenic precursor cells that are critical for muscle growth and regeneration. Growth hormone (GH) has been shown to play a role in the promotion of growth of skeletal muscle in mammals. GH administrated to pigs, ruminants, and humans has been found to increase skeletal muscle growth. Satellite cells are found beneath the basal lamina; when activated by signals which are not completely understood, they undergo proliferation and terminal differentiation to form new myofibers or fuse into others (Halevy, Hodik, & Mett, 1996; & Hodik, Mett, & Halevy, 1997).
Fibroblast growth factor (FGF) is a factor in satellite cell myogenesis for mammals and chickens; it is found to be the most potent inhibitor of myoblast differentiation. Heparin-binding FGFs show a constellation of physiological actions which include skeletal muscle regeneration and repression of skeletal myoblast differentiation. During the process of muscle cell differentiation, FGF receptors disappear from the cell surface and gene transcription is decreased. This may suggest the mediation of FGF's effects via its receptors. Binding to its receptor, FGF triggers a cascade of events (Hodik, Mett, & Halevy, 1997; & Templeton & Hauschka, 1992).
Although it has been shown that GH affect skeletal muscle satellite cell proliferation and differentiation, and it is known that FGFs and FGF receptors play major roles in control of skeletal muscle ...