ATP敏感钾通道在预先应用左旋甲状腺素钠对抗未成年大鼠离体心脏缺血-再灌注损伤中的作用

Role of Adenosine Triphosphate Sensitive Potassium Channel in Protection of Preemptive Levothyroxine-Sodium Administration Against Myocardial Ischemia-Reperfusion Injury in Isolated Immature Rat Heart Models

目的明确ATP敏感钾通道在预先应用左旋甲状腺素钠对抗未成年大鼠离体心脏缺血-再灌注损伤中的作用。方法将日龄35d的未成年健康雌性Wistar大鼠32只随机分为4组(每组8只):空白对照组(BC组)、对照组(C组)、左旋甲状腺素钠100μg组(100μg组)和格列本脲+左旋甲状腺素钠组(G+L组)。BC组和C组大鼠实验前应用普通饲料喂养7d;除普通饲料喂养外,100μg组和G+L组大鼠每天通过灌胃方式应用左旋甲状腺素钠100μg.kg-1进行预处理。第8天麻醉后取出大鼠心脏,采用Langendorff装置建立离体心脏缺血-再灌注模型,BC组离体心脏持续灌注80min,中间不实施停灌注,余各组的离体心脏则均顺序经历平衡30min、常温停灌注20min和再灌注30min处理。G+L组采用含有格列本脲30μmol.L-1的Krebs-Henseleit缓冲液(KH液)灌注,而其他组采用KH液灌注。实验中连续监测心率、收缩压、左心室压力上升的最大速率(dp/dtmax)和左心室压力下降的最大速率(dp/dtmin)等血流动力学指标;测定平衡期和再灌注期的冠脉流量及再灌注期冠脉流出液中心肌型肌酸激酶同工酶(CK-MB)活性;再灌注后取心室肌组织标本,采用Westernblot技术检测热休克蛋白70(HSP70)的表达,采用实时定量RT-PCR技术检测肌球蛋白重链(MHC)和甲状腺激素受体(TR)mRNA的表达。结果与C组比较,100μg组和G+L组再灌注期全部血流动力学指标及平衡期和再灌注期冠脉流量均显著增高,且100μg组和G+L组平衡期冠脉流量显著高于BC组。100μg组和G+L组再灌注期冠脉流出液CK-MB活性显著高于BC组,但显著低于C组。100μg组和G+L组心室肌组织HSP70和MHCαmRNA表达显著强于BC组和C组。100μg组和G+L组所有检测指标比较差异均无统计学意义。4组心室肌组织TRmRNA表达比较差异均无统计学意义。结论 ATP敏感钾通道可能与预先应用左旋甲状腺素钠对未成年大鼠离体心脏缺血-再灌注损伤的保护作用机制无关。

Objective To verify the role of adenosine triphosphate（ATP） sensitive potassium channel in protection of preemptive levo- thyroxine - sodium administration against myocardial ischemia - reperfusion injury in isolated inmmture rat heart models. Methods Thirty - two healthy,female immature （ aged 35 days） Wistar rats were randomly allocated into 4 groups （ n = 8 each ） ： blank control group （ group BC ）, control group （ group C ）, levothyroxine - sodlnm 100 μg group （ group 100 μg） and combined glibenclamide and levothyroxine - sodium group （ group G ＋ L）. The rats in group BC and group C were fed with normal food for 7 days before experiment. Except for feeding with normal food for 7 days before experiment,the rats in group 100 μg and group G ＋ L were also pretreatmented with levothyroxine sodium 100 μg·kg-1 , through a gastric tube every day. On the 8th day, the hearts were harvested front the anesthetized rats, and appended to a Langendorff apparatus for the isolated heart perfusion model. The isolated hearts in group BC were perfused for 80 minutes without zero - perfusion, whereas the hearts in other groups experienced in order a 30 minutes balance period, a 20 minutes normothermic zero - perfusion and a 30 minutes reperfu- sion period. The isolated hearts were perfused with Krebs - Henseleit fluid （ KH fluid） containing glibenclamide 30 μmol· L-1 in group G ＋ L, and with KH fluid in other groups, respectively. The hemodynamic variables including heart rate, systolic blood pressure, peak rates of rise in the first derivative of left ventricular pressure （ dp/dtm~＊ ） and peak rates of fall in the first derivative of left ventricular pressure （ dp/dtmio ） were continuously monitored. The coronary perfosion flow was recorded during balance and reperfusion periods. During reperfusion period, the coronary perfusion fluid was collected to assay the cardiac enzyme - myocardial - bound creatine kinase （ CK - MB）. At the end of perfusion, the ventricular muscle samples were taken to detect expression of heat shock protein 70 （HSP70） by Western blot, and expression of beth myo- globulin heavy chain（MHC） mRNA and thyroid hormone receptor （TR） mRNA by real -time quantitative reverse tronscription -polymerase chain reaction（ RT- PCR）. Results As compared with group C ,all hemodynamic variables during reperfusion period significantly increased in group 100 μg and group G ＋ L. The coronary perfusion flows in balance and reperfusion periods significantly increased in group 100 μg and group G ＋ L compared with group C. Also,the coronary perfusion flow in balance period significantly increased in group 100 μg and group G ＋L compared with group BC. The activity level of CK - MB in the coronary perfusion fluid during reperfusion period was significantly lower in group 100μg and group G ＋ L than in group C, but significantly higher in group 100 μg and group G ＋ L than in group BC. The ventricular myocardial expression of HSP70 significantly increased in group 100μg and group G ＋ L than in group BC and group C. The ventricular myocardial expression of MHCα mRNA significantly increased in group 100 μg and group G ＋ L compared with group BC and group C. However,there was no signifi- cant difference in all detected parameters between group 100 μg and group G ＋ L. Also, the ventricular myocardial expression of TR mRNA was not significantly different among 4 groups. Conclusions ATP sensitive potassium channel is not probably involved in the mechanism of protection by preemptive levothyroxine - sodium administration against myocardial ischemia - reperfusion injury in isolated immature rat heart models.