Moussavi R, Meisami E, Timiras P S
Department of Physiology-Anatomy, University of California, Berkeley 94720.
Mech Ageing Dev. 1988 Nov 30;45(3):285-97. doi: 10.1016/0047-6374(88)90009-7.
Postnatal growth of skeletal muscle (m. gastrocnemius) was compared in rats under euthyroid, hypothyroid and hypothyroid-rehabilitated conditions. In normal (euthyroid) animals, gastrocnemius muscle grows significantly in terms of weight (150 x) from birth to the young adult and, in terms of total contractile myofibril protein (15 x) and myosin ATPase activity (10 x) between days 25 and 90. Rats made hypothyroid (with 0.1% w/v propylthiouracil, PTU) from birth show reduced growth. At 25 days (weaning), compared with euthyroid, muscle weight is only 25% of normal, and a similar reduction is found in total DNA, RNA, protein, myofibril protein, and myosin ATPase activity. These deficits, already significant by day 10, are more marked by day 50 due to the near arrest of growth. Hypothyroid rats allowed to recover by PTU withdrawal after day 25 (rehabilitated) undergo marked compensatory muscle growth. By day 90, muscle weight and protein content increase 50 x, DNA 7 x and RNA 17 x. Over this period, total myofibrillar protein and myosin ATPase increase 20-40 x, but are still below those of 90-day controls, suggesting that the severe growth retardation had not yet been fully compensated. Early thyroid deficiency drastically reduces the normal age-related growth of skeletal muscle and severely retards the development of contractile elements, affecting muscle hypertrophy (protein content) more than cell proliferation (DNA content). Rehabilitation compensates to a major degree for this growth retardation. These results underline the key role of thyroid hormones in regulating development and maturation of skeletal muscle throughout the preweaning and postweaning phases of growth.
对处于甲状腺功能正常、甲状腺功能减退和甲状腺功能减退恢复状态的大鼠的骨骼肌（腓肠肌）的出生后生长情况进行了比较。在正常（甲状腺功能正常）动物中，腓肠肌重量从出生到年轻成年期显著增加（增加150倍），在25至90日龄期间，总收缩肌原纤维蛋白（增加15倍）和肌球蛋白ATP酶活性（增加10倍）。从出生起就用0.1%（w/v）丙硫氧嘧啶（PTU）造成甲状腺功能减退的大鼠生长减缓。在25日龄（断奶时），与甲状腺功能正常的大鼠相比，肌肉重量仅为正常的25%，总DNA、RNA、蛋白质、肌原纤维蛋白和肌球蛋白ATP酶活性也有类似程度的降低。这些缺陷在第10天时就已很明显，到第50天时由于生长几乎停滞而更加显著。25日龄后通过停用PTU而恢复的甲状腺功能减退大鼠会经历明显的肌肉代偿性生长。到90日龄时，肌肉重量和蛋白质含量增加50倍，DNA增加7倍，RNA增加17倍。在此期间，总肌原纤维蛋白和肌球蛋白ATP酶增加20 - 40倍，但仍低于90日龄对照组，这表明严重的生长迟缓尚未得到完全补偿。早期甲状腺功能缺乏会大幅降低骨骼肌正常的与年龄相关的生长，并严重阻碍收缩元件的发育，对肌肉肥大（蛋白质含量）的影响大于细胞增殖（DNA含量）。恢复过程在很大程度上补偿了这种生长迟缓。这些结果强调了甲状腺激素在调节整个断奶前和断奶后生长阶段骨骼肌发育和成熟中的关键作用。
