Relationship between myostatin and muscle enlargement during exercise and growth

我们检测了垂体切除和营养不良大鼠在出生后生长过程中骨骼肌中肌生长抑制素mRNA的表达（实验1）。将5周龄大鼠分为4组：自由喂养组（NC）、中度饥饿组（MU）、重度饥饿组（SU）和垂体切除组（HX）。比目鱼肌、跖肌和咬肌重量以NC组最高，MU组次之。SU和HX的体重最低。各组比目鱼肌MHC亚型无差异。HX组跖肌中I型MHC显著增加，而II型MHC则显著减少。新生儿的MHC亚型在HX咬肌显着增加，在牺牲IIx型和IIb型。HX组跖肌和咬肌肌生长抑制素mRNA水平显著低于SU组，MU组和SU组显著高于NC组。我们检测了垂体切除术和代偿性过载后跖肌中肌生长抑制素mRNA的表达（实验2）。将9周龄大鼠分为正常对照组（NC）、正常超载组（NOL）、去垂体对照组（HxC）和去垂体超载组（HxOL）。代偿性超负荷后21天，NOL组的跖肌重量显著高于NC组。HxOL组的体重显著高于HxC组。切除垂体后，HxC组的跖肌重量显著低于NC组。代偿性超负荷后3、21 d，HxOL组跖肌肌生长抑制素mRNA水平显著低于HxC组。NC和NOL之间的肌肉生长抑制素mRNA水平无差异。我们的结论是，抑制肌肉生长，由于垂体切除术和喂养不足，以及肌肉肥大，由于补偿性超负荷与肌肉生长抑制素的表达。

We examined myostatin mRNA expression in skeletal muscle of hypophysectomized and underfed rats during postnatal growth (experiment 1). Five-week old rats were divided into 4 groups : freely fed (NC), moderately underfed (MU), severely underfed (SU) and hypophysectomized (HX). The weights of soleus, plantaris and masseter muscles in NC were highest followed by those in MU. The lowest weights were in SU and HX. There were no differences in soleus muscle MHC isoforms between groups. Type I MHC in plantaris muscle in HX was increased significantly at the expense of type IIx. The neonatal MHC isoform in masseter muscle in HX was increased significantly at the expense of types IIx and IIb. Plantaris and masseter muscle myostatin mRNA levels in HX were significantly lower than those in SU, and levels in MU and SU were significantly higher than those in NC. We examined myostatin mRNA expression in plantaris muscle following hypophysectomy and compensatory overload (experiment 2). Nine-week old rats were divided into 4 groups: normal control (NC), normal overloaded (NOL), hypophysectomized control (HxC) and hypophysectomized overloaded (HxOL). The weights of plantaris muscle in NOL were significantly higher than those of NC 21 days after compensatory overload. The weights in HxOL were significantly higher than those of HxC. By hypophysectomy, the weights of plantaris muscle in HxC were significantly lower than those of NC. Myostatin mRNA levels of plantaris muscle in HxOL 3 and 21 days after compensatory overload were significantly lower than those in HxC. There were no differences in myostatin mRNA levels between NC and NOL. We conclude that suppressed muscle growth due to hypophysectomy and underfeeding as well as muscle enlargement due to compensatory overload were associated with the expression of myostatin.