Effects of cold exposure on cardiovascular function and skeletal muscle contraction in rats / 中国医师杂志

ABSTRACT

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/cm2 vs (5.50 ± 0.75) N/cm2,P ＜ 0.05 and (3.00 ± 0.57) N/ cm2 vs (4.70 ± 0.85) N/cm2,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.