Skeletal muscle repair in a rat muscle injury model: the role of growth hormone (GH) injection

OBJECTIVE: Muscle injury tends to heal with incomplete functional recovery. Among the growth factors released in the physio-pathological response of muscle lesion. the Insulin-like Growth-Factor-1 (IGF-1) results in an engine factor of the reparation program. The therapeutic use of growth factors has been exploited to improve healing. As IGF-1 is a primary mediator of the effects of growth hormone (GH). we exploited its systemic administration to muscle recovery in a rat model of muscle injury. MATERIALS AND METHODS: Monolateral lesion of the longissimus dorsi muscle of rats was performed. Animals were divided into 5 groups: four groups for histological studies and serum hormone dosage, whilst the fifth group represented the uninjured control. Rat GH was intraperitoneally administered after 24h from the surgical lesion at three different concentrations (0.1, 0.2. 0.4 mg/kg). At 3 days from surgery. immunohistochemical and histological analyses evaluated the expression of MyoD and Myogenin, and the presence of neovascularization and inflammation, respectively. After 2 months, we analyzed the presence of muscle regeneration and fibrosis. RESULTS: The treatment with GH resulted in a significant increase in neovascularization and Myogenin expression at 24h from injury in comparison with the control. This suggested speed up biological recovery times. After two-months, a dose-dependent increase of the connective component was observed. CONCLUSIONS: The potential effect of GH on muscle repair and regeneration, through the activation of satellite cells already demonstrated in vitro, was confirmed in this in vivo experimental approach. This study sheds light on the role of growth factors in damage repair mechanisms to find an appropriate biological treatment for muscle injury.