Relationship between myostatin and muscle enlargement during exercise and growth

我们检测了骨骼肌中肌生长抑制素mRNA的表达（实验1）。将5周龄大鼠分为自由喂养组（NC）、中度不足喂养组（MU）、严重不足喂养组（SU）和垂体切除组（HX）。NC组比目鱼肌、跖肌和咬肌的重量最大，MU组次之。体重最低的是SU和HX。各组间比目鱼肌MHC异构体无差异。HX组足底肌中I型MHC显著增加，而IIx组则明显减少。HX型新生儿咬肌MHC异构体显著增加，IIx型和IIb型新生儿则明显增加。HX组足底肌和咬肌肌生长抑制素mRNA水平显著低于SU组，MU和SU组显著高于NC组。我们检测了垂体切除术和代偿超负荷后足底肌肉中肌生长抑制素mRNA的表达（实验2）。9周龄大鼠分为4组：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）。代偿超负荷21 d后，NOL组足底肌重量显著高于NC组。HxOL的重量显著高于HxC。经垂体切除术，HxC大鼠足底肌重量显著低于NC大鼠。代偿超负荷后HxOL 3和21 d足底肌肉肌肉生长抑制素mRNA水平显著低于HxC组。肌生长抑制素mRNA水平在NC和NOL之间无差异。我们得出结论，垂体切除术和摄食不足导致的肌肉生长抑制以及代偿性过载导致的肌肉扩张与肌肉生长抑制素的表达有关。

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.