Finkelstein D I, Andrianakis P, Luff A R, Walker D W
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Am J Physiol. 1992 Oct;263(4 Pt 2):R900-8. doi: 10.1152/ajpregu.1992.263.4.R900.
In this study, plasma thyroxine, contractile and histochemical (adenosinetriphosphatase and NADH) characteristics of soleus (SOL), medial gastrocnemius (MG), and extensor digitorum longus (EDL) were examined in 140-day-gestation fetal sheep and in 2-, 5-, and 30-day-old lambs and adult ewes. Electrophoretic separation of myosin heavy chains was also done on all muscles and the diaphragm. There were no differences in the twitch contraction and relaxation times of MG and EDL at the different ages; in contrast SOL contraction times were significantly shorter in the fetus and newborn than in the adult. Fast glycolytic fibers first appeared in EDL, MG, and diaphragm at 5, 30, and 5 days after birth, respectively. The proportion of slow oxidative fibers decreased after birth and with postnatal development in EDL, whereas they increased in MG and diaphragm. Plasma thyroxine concentrations were higher in the fetus and day-old lambs than in 2-, 5-, and 30-day-old lambs or adult sheep. It is suggested that contractile specialization of the fast-twitch diaphragm, MG, and EDL is largely achieved in utero and is probably mediated by thyroid hormone. In contrast, SOL changed postnatally, probably influenced by the altered neural drive.
在本研究中，对妊娠140天的胎羊、2日龄、5日龄、30日龄的羔羊以及成年母羊的比目鱼肌（SOL）、内侧腓肠肌（MG）和趾长伸肌（EDL）的血浆甲状腺素、收缩特性和组织化学特性（三磷酸腺苷酶和烟酰胺腺嘌呤二核苷酸）进行了检测。还对所有肌肉和膈肌进行了肌球蛋白重链的电泳分离。不同年龄的MG和EDL的抽搐收缩和舒张时间没有差异；相比之下，胎儿和新生儿的SOL收缩时间明显短于成年羊。快速糖酵解纤维分别在出生后5天、30天和5天首次出现在EDL、MG和膈肌中。出生后，随着出生后发育，EDL中慢氧化纤维的比例下降，而在MG和膈肌中则增加。胎儿和日龄羔羊的血浆甲状腺素浓度高于2日龄、5日龄、30日龄的羔羊或成年羊。提示快速抽搐的膈肌、MG和EDL的收缩特化在子宫内基本完成，可能由甲状腺激素介导。相比之下，SOL在出生后发生变化，可能受神经驱动改变的影响。
