GROWTH HORMONES/FACTORS & MUSCLE CELLS Abstract

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 di

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t, and Halevy used male broiler chicks; skeletal muscle satellite cells were cultured from the pectoral muscle. DNA synthesis was assessed by thymidine incorporation. Cells were treated with various factors. Total RNA was isolated with guanidinium-thiocyanate-phenol technique. Analysis of variance determined differences between treatments. Templeton and Hauschka used murine 3T3-D1 cells for their study. All cell lines were grown on gelatin-coated culture dishes. Differentiated MM14 myocytes and quiescent DD-1 cells were from switching cell cultures to low serum medium lacking bFGF. RNA blot analysis and RNase protection assays were included. Total RNA from tissue culture cells was isolated. Also performed were transcription reactions to generate antisense radiolabeled RNA probe. Genomic PCR clones were isolated. Results Halevy, Hodik, and Mett report findings that GH-R gene expression was regulated by cGH and it correlated with GH effect on cell proliferation. Results showed that 2-10 ng/ml hormone increased GH-R mRNA and DNA synthesis and higher concentrations decreased these effects. GH induced insulin-like growth factor I (IGF-I) mRNA which is a potential factor for satellite cell proliferation and differentia
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Approximate Word count = 1450
Approximate Pages = 6 (250 words per page)