Altered in vivo left ventricular torsion and principal strains in hypothyroid rats
Altered in vivo left ventricular torsion and principal strains in hypothyroid rats
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DOI：
10.1152/ajpheart.00406.2010
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发表时间：
2010-11-01
影响因子：
4.8
通讯作者：
Stelzer, Julian E.
中科院分区：
文献类型：
--
作者：
Chen, Yong;Somji, Aleefia;Stelzer, Julian E.
陈勇，颂吉，余旭，施特尔策，JE。甲状腺功能减退大鼠在体左室扭转和主应变的变化。Am J Physiol心脏圈Physiol 299：H1577-H1587,2010。2010年8月20日首次出版；DOI：10.1152/ajpheart.00406.2010。-左心室(LV)的扭转和解旋运动导致收缩期间有效的血液射出和舒张期心室的充盈。整体的左心室机械性能取决于心肌细胞的收缩特性；然而，收缩蛋白表达的变化如何影响左心室旋转的模式和时间尚不清楚。在肌丝水平上，收缩性能在很大程度上取决于表达的肌球蛋白重链(MHC)的异构体。因此，在这项研究中，我们使用MRI来检测体内MHC亚型表达变化的力学后果，方法是比较甲状腺功能低下大鼠和正常甲状腺大鼠的收缩特性，甲状腺功能低下大鼠只表达缓慢的β-MHC亚型，正常大鼠主要表达快速α-MHC亚型。本文测定了甲状腺功能正常和甲状腺功能减退心脏去皮心肌的无负荷缩短速度(V-o)和表观力量发展速率常数(k(Tr))。β-MHC的表达增加，减少了左室扭转和纤维应变，延缓了收缩期峰扭转和应变的发展。与甲状腺功能正常的大鼠相比，甲状腺功能低下的大鼠体内机械性能的降低与跨桥性能的减慢有关，这一点从V-o和k(Tr)显著减慢来表明。在甲状腺功能减退的心脏中注射多巴酚丁胺产生较小的扭转和应变增加以及异常的跨室壁扭转模式，这表明心肌对β-肾上腺素能应激的反应受到损害。因此，β-MHC的表达增加改变了型式，减少了左室旋转的幅度，导致收缩期间机械性能降低，特别是在负荷增加的情况下。
Chen Y, Somji A, Yu X, Stelzer JE. Altered in vivo left ventricular torsion and principal strains in hypothyroid rats. Am J Physiol Heart Circ Physiol 299: H1577-H1587, 2010. First published August 20, 2010; doi:10.1152/ajpheart.00406.2010.-The twisting and untwisting motions of the left ventricle (LV) lead to efficient ejection of blood during systole and filling of the ventricle during diastole. Global LV mechanical performance is dependent on the contractile properties of cardiac myocytes; however, it is not known how changes in contractile protein expression affect the pattern and timing of LV rotation. At the myofilament level, contractile performance is largely dependent on the isoforms of myosin heavy chain (MHC) that are expressed. Therefore, in this study, we used MRI to examine the in vivo mechanical consequences of altered MHC isoform expression by comparing the contractile properties of hypothyroid rats, which expressed only the slow beta-MHC isoform, and euthyroid rats, which predominantly expressed the fast alpha-MHC isoform. Unloaded shortening velocity (V-o) and apparent rate constants of force development (k(tr)) were measured in the skinned ventricular myocardium isolated from euthyroid and hypothyroid hearts. Increased expression of beta-MHC reduced LV torsion and fiber strain and delayed the development of peak torsion and strain during systole. Depressed in vivo mechanical performance in hypothyroid rats was related to slowed cross-bridge performance, as indicated by significantly slower V-o and k(tr), compared with euthyroid rats. Dobutamine infusion in hypothyroid hearts produced smaller increases in torsion and strain and aberrant transmural torsion patterns, suggesting that the myocardial response to beta-adrenergic stress is compromised. Thus, increased expression of beta-MHC alters the pattern and decreases the magnitude of LV rotation, contributing to reduced mechanical performance during systole, especially in conditions of increased workload.