长期甲状腺素刺激对大鼠心肌Ca /钙调蛋白依赖性蛋白激酶Ⅱ的影响

目的: 通过观察长期甲状腺素刺激对心肌Ca²⁺/钙调蛋白依赖性蛋白激酶Ⅱ(CaMKII)的影响,探讨CaMKII是否参与甲亢性心脏病的发生发展。方法: 将20只SD大鼠随机分为甲状腺素刺激组和对照组,每组各10只。以0.2 mg·kg^-1·d^-1的剂量腹腔注射甲状腺素或等体积生理盐水3个月(每次给药前称体重),造模后3个月处死大鼠。以心重(HW)、心重与体重之比(HW/BW)、左心室重与体重之比(LVW/BW)及心肌细胞直径大小反映心肌肥厚;以心肌血管周围胶原面积(PVCA)/血管腔面积(VA)的比值反映心肌纤维化。用实时定量RT-PCR和Western blotting分别从mRNA水平和蛋白表达水平反映CaMKII的变化。结果: 造模3个月后与对照组相比,甲状腺素刺激组的HW/BW、LVW/BW、心肌细胞直径大小和心肌纤维化程度(PVCA/VA)均明显高于对照组,分别是对照组的1.87、1.84、2.15和1.94倍,差异均显著(P<0.05,P<0.01);甲状腺素刺激组心肌细胞中CaMKII mRNA表达水平、蛋白含量与对照组相比均降低,分别是对照组的40%和79%,但CaMKII的活性较对照组增加1.58倍,其差异均显著(P<0.05)。结论: 长期甲状腺素刺激诱导大鼠心肌肥厚模型中,甲状腺素降低心肌CaMKII的表达,但心肌CaMKII的活性增加,CaMKII可能参与甲状腺素诱导的甲亢性心脏病的发生发展。

Effect of chronic administration of L-thyroxine on Ca2+/calmodulin-dependent protein kinase II in rat myocardium

AIM: To investigate the effect of chronic injection of L-thyroxine on Ca2+/calmodulin-dependent protein kinase II(CaMKII) and to explore whether CaMKII directly mediates hyperthyroidism-induced cardiac hypertrophy.METHODS: Twenty male Sprague-Dawley rats were randomly divided into hyperthyroid group and control group with 10 animals each.The animal model was produced by intraperitoneal injection of L-thyroxine(0.2 mg·kg-1·d-1) for 3 months.The control animals only received saline vehicle in the same procedures.Heart weight(HW),heart-to-body weight ratio(HW/BW),left ventricular-to-body weight ratio(LVW/BW) and diameter of cardiac myocytes were measured to evaluate cardiac hypertrophy.The ratio of perivascular collagen area to vascular luminal area(PVCA/VA) was used to represent myocrdial fibrosis.Moreover,the mRNA expression of CaMKII and the protein level of CaMKII were measured by real-time RT-PCR and Western blotting,respectively.RESULTS: Intraperitoneal injection of L-thyroxine for 3 months significantly increased HW/BW,LVW/BW,PVCA/VA and diameter of cardiac myocytes by 1.87,1.84,1.94 and 2.15 folds,respectively(P<0.05 or P<0.01) as compared with control group.The results of real-time RT-PCR revealed that L-thyroxine injection caused a 60% reduction in the mRNA level of cardiac CaMKII(P<0.05).Furthermore,the results of Western blotting confirmed that the protein expression level of cardiac CaMKII in L-thyroxine group diminished by 21%(P<0.05),but accompanied by a 1.58-fold enhancement of phosphorylated activity of CaMKII(P<0.05).CONCLUSION: Thyroxine decreases the expression level of cardiac CaMKII and increases the activity of CaMKII in the chronic hyperthyroid-induced hypertrophic heart,suggesting that CaMKII participates in the formation and maintenance of cardiac hypertrophy induced by hyperthyroidism in a balanced way.