Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Anim Sci. 2012 Apr;90(4):1126-33. doi: 10.2527/jas.2011-4358. Epub 2011 Nov 18.
Growth hormone is a major stimulator of skeletal muscle growth in animals, including cattle. In this study, we determined whether GH stimulates skeletal muscle growth in cattle by direct stimulation of proliferation or fusion of myoblasts, by direct stimulation of protein synthesis, or by direct inhibition of protein degradation in myotubes. We also determined whether these direct effects of GH are mediated by IGF-I produced by myoblasts or myotubes. Satellite cells were isolated from cattle skeletal muscle and were allowed to proliferate as myoblasts or induced to fuse into myotubes in culture. Growth hormone at 10 and 100 ng/mL increased protein synthesis in myotubes (P < 0.05), but had no effect on protein degradation in myotubes or proliferation of myoblasts (P > 0.05). Insulin-like growth factor-I at 50 and 500 ng/mL stimulated protein synthesis (P < 0.01), and this effect of IGF-I was much greater than that of GH (P < 0.05). Besides stimulating protein synthesis, IGF-I at 50 and 500 ng/mL also inhibited protein degradation in myotubes (P < 0.01), and IGF-I at 500 ng/mL stimulated proliferation of myoblasts (P < 0.05). Neither GH nor IGF-I had effects on fusion of myoblasts into myotubes (P > 0.1). These data indicate that GH and IGF-I have largely different direct effects on bovine muscle cells. Growth hormone at 10 and 100 ng/mL had no effect on IGF-I mRNA expression in either myoblasts or myotubes (P > 0.1). This lack of effect was not because the cultured myoblasts or myotubes were not responsive to GH; GH receptor mRNA was detectable in them and the expression of the cytokine-inducible SH2-containing protein (CISH) gene, a well-established GH target gene, was increased by GH in bovine myoblasts (P < 0.05). Overall, the data suggest that GH stimulates skeletal muscle growth in cattle in part through stimulation of protein synthesis in the muscle and that this stimulation is not mediated through increased IGF-I mRNA expression in the muscle.
生长激素是动物（包括牛）骨骼肌肉生长的主要刺激物。在这项研究中，我们确定 GH 是否通过直接刺激成肌细胞的增殖或融合、直接刺激蛋白质合成、或直接抑制肌管中的蛋白质降解来刺激牛的骨骼肌肉生长。我们还确定了 GH 的这些直接作用是否通过成肌细胞或肌管产生的 IGF-I 介导。卫星细胞从牛骨骼肌中分离出来，在培养中增殖为成肌细胞或诱导融合为肌管。10 和 100ng/mL 的生长激素增加了肌管中的蛋白质合成（P<0.05），但对肌管中的蛋白质降解或成肌细胞的增殖没有影响（P>0.05）。50 和 500ng/mL 的胰岛素样生长因子-I 刺激蛋白质合成（P<0.01），IGF-I 的这种作用比 GH 强得多（P<0.05）。除了刺激蛋白质合成外，50 和 500ng/mL 的 IGF-I 还抑制了肌管中的蛋白质降解（P<0.01），500ng/mL 的 IGF-I 刺激了成肌细胞的增殖（P<0.05）。GH 和 IGF-I 对成肌细胞融合成肌管都没有影响（P>0.1）。这些数据表明，GH 和 IGF-I 对牛肌肉细胞有很大的不同的直接作用。10 和 100ng/mL 的 GH 对成肌细胞或肌管中的 IGF-I mRNA 表达没有影响（P>0.1）。这种没有影响并不是因为培养的成肌细胞或肌管对 GH 没有反应；它们中可检测到 GH 受体 mRNA，GH 增加了牛成肌细胞中细胞因子诱导的 SH2 含有蛋白（CISH）基因的表达，CISH 基因是一个已确立的 GH 靶基因（P<0.05）。总的来说，这些数据表明，GH 通过刺激肌肉中的蛋白质合成来刺激牛的骨骼肌肉生长，而这种刺激不是通过肌肉中 IGF-I mRNA 表达的增加来介导的。
