Yamaguchi A, Fujikawa T, Tateoka M, Soya H, Sakuma K, Sugiura T, Morita I, Ikeda Y, Hirai T
School of Dentistry, Health Sciences University of Hokkaido, Kanazawa, Ishikari-Tobetsu, Hokkaido, Japan.
Acta Physiol (Oxf). 2006 Apr;186(4):291-300. doi: 10.1111/j.1748-1716.2006.01569.x.
To determine the roles of myostatin and insulin-like growth factor-I (IGF-I) during postnatal growth, we examined IGF-I and myostatin mRNA expression in the skeletal muscles of hypophysectomized and underfed rats during postnatal growth.
Five-week-old rats were divided into four groups: freely fed control, moderately underfed, severely underfed and hypophysectomized. Four weeks later, blood and muscle samples were gathered to determine serum IGF-I, myosin heavy chain (MHC) isoforms, IGF-I Ea, IGF-I Eb and myostatin mRNA.
The weights of soleus, plantaris and masseter muscles were decreased in underfed and hypophysectomized rats. Hypophysectomy resulted in significant increases of type I MHC at the expense of type IIx in plantaris muscle and of neonatal MHC at the expense of types IIx and IIb in masseter muscle. Serum IGF-I was decreased by underfeeding and hypophysectomy. Plantaris muscle IGF-I Ea mRNA in underfed and hypophysectomized rats was significantly lower than in normal controls. Plantaris muscle IGF-I Eb mRNA in underfed rats was significantly lower than in normal controls. Masseter muscle IGF-I Eb mRNA in severely underfed rats was significantly lower than in normal control and hypophysectomized rats. Soleus muscle myostatin mRNA in hypophysectomized rats was significantly higher than in normal and significantly underfed rats. No significant differences in plantaris and masseter muscle myostatin mRNA were observed between groups.
Suppressed muscle growth caused by hypophysectomy and underfeeding may be attributed mainly to reduced circulating IGF-I and partially to reduced IGF-I mRNA, rather than to a change in myostatin.
为了确定肌肉生长抑制素和胰岛素样生长因子-I（IGF-I）在出生后生长过程中的作用，我们检测了出生后生长期间垂体切除和进食不足大鼠骨骼肌中IGF-I和肌肉生长抑制素mRNA的表达。
将5周龄大鼠分为四组：自由进食对照组、中度进食不足组、重度进食不足组和垂体切除组。四周后，采集血液和肌肉样本以测定血清IGF-I、肌球蛋白重链（MHC）亚型、IGF-I Ea、IGF-I Eb和肌肉生长抑制素mRNA。
进食不足和垂体切除大鼠的比目鱼肌、跖肌和咬肌重量降低。垂体切除导致跖肌中I型MHC显著增加，IIx型减少，咬肌中新生儿MHC显著增加，IIx型和IIb型减少。进食不足和垂体切除使血清IGF-I降低。进食不足和垂体切除大鼠的跖肌IGF-I Ea mRNA显著低于正常对照组。进食不足大鼠的跖肌IGF-I Eb mRNA显著低于正常对照组。重度进食不足大鼠的咬肌IGF-I Eb mRNA显著低于正常对照组和垂体切除大鼠。垂体切除大鼠的比目鱼肌肌肉生长抑制素mRNA显著高于正常和重度进食不足大鼠。各组间跖肌和咬肌肌肉生长抑制素mRNA无显著差异。
垂体切除和进食不足引起的肌肉生长抑制可能主要归因于循环IGF-I减少，部分归因于IGF-I mRNA减少，而非肌肉生长抑制素的变化。
