不同时程寒冷对大鼠心血管功能和骨骼肌收缩力的影响

Effects of cold exposure on cardiovascular function and skeletal muscle contraction in rats

目的 观察不同时程寒冷对大鼠心血管功能与骨骼肌收缩力的影响.方法 取成年雄性SD大鼠,制备不同时程的寒冷动物模型,实验分（1）正常对照组、（2）寒冷12 h组、（3）寒冷24 h组、（4）寒冷48 h组;各寒冷组大鼠均置于4℃环境中,但可自由进食和饮水.经上述处理后,麻醉下迅速分离大鼠心脏、胸主动脉、比目鱼肌和趾长伸肌,分别连实验灌流装置和数据记录系统;离体心脏采用Langendorff灌流,先记录冠脉流量（CF）、左心室平均收缩压（mLVSP）、平均舒张压（mLVDP）、左心室平均压（mLVP）和左室内压最大上升与下降速率（±dP/dt max）等心功能指标,再进行心脏缺血-再灌注,并记录上述心功能指标的变化;用器官浴槽法检测主动脉环收缩与内皮依赖性舒张反应;用电刺激法分别检测比目鱼肌和趾长伸肌的单次和强直收缩的最大张力.结果 与正常对照组相比,寒冷24～48 h明显降低大鼠CF[（9.0±1.7） ml/g和（9.8±1.3）ml/g vs（11.6±1.2）ml/g,P＜0.05],寒冷48 h还增加mLVSP（P＜0.01）和mLVP（P＜0.05）;在心肌缺血再灌注后,寒冷12～ 48 h均可缩短大鼠心脏复跳时间（均P ＜0.01）,但寒冷24 ～48 h明显升高缺血再灌注后mLVDP和mLVP（均P＜0.01）;在血管环实验中,寒冷24 ～48 h均可降低血管环对60 mmol/L氯化钾[（0.63±0.13）g和（0.79±0.11）g vs （1.28±0.17）g,P＜0.01]和1μmol/L苯肾上腺素[（0.62±0.18）g和（0.68±0.13）g vs （1.25 ±0.18）g,P＜0.01]诱导的血管收缩反应,但增加血管环对低浓度（3×10^-8 ～3×10^-7）乙酰胆碱诱导的内皮依赖性舒张反应（P＜0.05）;寒冷48 h还降低了比目鱼肌和趾长伸肌对电刺激诱导的强直收缩张力[（4.14±0.62） N/cm^2 vs （5.50±0.75） N/cm^2,P ＜0.05;（3.00±0.57）N/cm^2 vs （4.70±0.85） N/cm^2,P ＜0.01].结论 4℃寒冷24 ～ 48 h可降低冠脉血流量,可增强大鼠心脏对缺血再灌注损伤的耐受;寒冷24～48 h可降低血管收缩并增加ACh诱导血管内皮依赖性舒张的敏感性;寒冷48 h减弱骨骼肌对电刺激的收缩功能.

Objective To investigate the effects of cold exposure with different time courses on cardiovascular function and skeletal muscle contraction in Sprague-Dawley （SD） rats.Methods The male SD rats were randomly divided into control,12-h cold,24-h cold,and 48-h cold groups.The rats in all cold group were maintained in 4 ℃ environment for indicated time and allowed free access to standard rat chow and water ad libitum.After the animal model was established,the heart,thoracic aorta,soleus,and extensor digitorum longus （EDL） were rapidly isolated from rats under anesthesia and then fixed into the respective organ perfusion system that was connected to physiological recorders and data acquisition system.Lanendorff heart persusion was used to detect some parameters of cardiac function,such as coronary flow （CF）,mean left ventricular systolic pressure （mLVSP）,mean left ventricular diastolic pressure （mLVDP） and maximum ascending and declining rate of left ventricular pressure （± dp/dt max） ; and then the heart was suffered from 30 min ischemia followed by 60 min reperfusion,the changes of above cardiac function indexes were recorded again.Organ bath method was employed to detect contraction response to potassium chloride （KCl） or phenylephrine （PE） and endothelium-dependent relation responses to acetylcholine （ACh） of aortic rings.The twitch tension,titanic tension,and fatigue test of soleus and EDL were examined by electrical stimulation to reflect contractive function of skeletal muscle.Results The coronary flow （CF） were significantly reduced in 24-h and 48-h cold groups compared to control group [（9.0 ± 1.7） ml/g and （9.8 ± 1.3） ml/g vs （11.6 ± 1.2） ml/g,P 〈 0.05] ; 48-h cold exposure also showed significantly increased mLVSP （P 〈0.01） and mLVP （P 〈 0.05） of rats.After ischemia-reperfusion,the heart re-beat time was shorter in all cold exposure groups （all P 〈 0.01）,mLVP and mLVDP were higher in 24-h and 48-h cold group than control group （all P 〈 0.01）.The contraction of aortic rings responses to 60 mmol/L KCl [（0.63 ±0.13） g and （0.79 ±0.11）g vs （1.28±0.17）g,P 〈0.01] and 1 μmol/L PE [（0.62 ±0.18）g and （0.68 ±0.13）g vs （1.25 ± 0.18）g,P 〈 0.01] were decreased while the endothelium-dependent relaxation responses to low concentration ACh （3× 10^-8 ～ 3 ×10^-7） were increased in 24-h and 48-h cold groups relative to control group （all P 〈 0.05）.The 48-h cold also reduced titanic tension of SOL and EDL in comparison with control [（4.14 ± 0.62） N/cm^2 vs （5.50 ± 0.75） N/cm^2,P 〈 0.05 and （3.00 ± 0.57） N/ cm^2 vs （4.70 ± 0.85） N/cm^2,P 〈 0.01].Conclusions 24 ～ 48 h cold exposure could reduce CF but enhance the tolerance of heart from rats to ischemia reperfusion injury and also decrease the contraction of aortic rings response to KCl or PE but increase the sensitive responses to ACh of aortic rings from rats.The 48-h cold could decrease the contraction of skeletal muscle elicited by electrical stimulation.