Cappelli V, Moggio R, Polla B, Bottinelli R, Poggesi C, Reggiani C
Institute of Human Physiology, University of Pavia, Italy.
Pflugers Arch. 1988 Jun;411(6):620-7. doi: 10.1007/BF00580857.
This study was designed to investigate the changes in cardiac contractile properties induced by triiodothyronine (T3) administration in adult rats. Myofibrils and myosin were isolated from ventricular muscles from euthyroid and hyperthyroid animals and enzymatically and electrophoretically characterized. The time course of the isometric response, the force velocity curve, the force interval relation were studied in papillary muscles isolated from the right ventricles of euthyroid and hyperthyroid rats. T3 administration induced significant increases in Mg2+ activated myofibrillar ATPase activity (+11.4%) and in Ca2+ activated myosin ATPase activity (+20.1%). Significant increases in shortening velocity at low and zero loads (+20.4%) were found in papillary muscles from treated animals when compared with the control muscles. These variations in enzymatic activity and shortening velocity could be related to the increase in the amount of the fast isomyosin V1, as shown by pyrophosphate gel electrophoresis. The negative force-frequency relation at steady state, typical of rat cardiac preparations, was observed in treated and control animals; its slope was, however, halved in hyperthyroid papillary muscles when compared with control ones. In accordance with this finding, the potentiating effect of a prolonged diastolic interval was significantly reduced in hyperthyroid papillary muscles. In the frame of an interpretation of the force interval relation on the basis of the excitation contraction coupling processes, these latter observations might indicate an enhanced activity of the sarcoplasmic reticulum. We conclude that thyroid hormone administration has a dual effect on cardiac contractility, on one hand regulating the synthesis of the different isomyosin and, on the other hand, stimulating the activity of the sarcoplasmic reticulum.
本研究旨在探讨成年大鼠给予三碘甲状腺原氨酸（T3）后心脏收缩特性的变化。从甲状腺功能正常和甲状腺功能亢进动物的心室肌中分离出肌原纤维和肌球蛋白，并对其进行酶学和电泳特性分析。研究了从甲状腺功能正常和甲状腺功能亢进大鼠右心室分离出的乳头肌的等长收缩反应的时间进程、力-速度曲线、力-间期关系。给予T3后，Mg2+激活的肌原纤维ATP酶活性显著增加（+11.4%），Ca2+激活的肌球蛋白ATP酶活性显著增加（+20.1%）。与对照肌肉相比，处理动物的乳头肌在低负荷和零负荷下的缩短速度显著增加（+20.4%）。焦磷酸凝胶电泳显示，酶活性和缩短速度的这些变化可能与快速同型肌球蛋白V1含量的增加有关。在处理组和对照组动物中均观察到大鼠心脏标本典型的稳态负力-频率关系；然而，与对照组相比，甲状腺功能亢进乳头肌的斜率减半。根据这一发现，甲状腺功能亢进乳头肌中舒张间期延长的增强作用显著降低。在基于兴奋-收缩偶联过程解释力-间期关系的框架内，这些观察结果可能表明肌浆网的活性增强。我们得出结论，给予甲状腺激素对心脏收缩力有双重作用，一方面调节不同同型肌球蛋白的合成，另一方面刺激肌浆网的活性。
