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AIM:To investigate the influence of calorie restriction ( CR) on contractility and mitochondrial bi-osynthesis in different types of rat skeletal muscles .METHODS:CR rat model was set up by feeding 60%normal food in-take of control rat every day for 8 weeks.Soleus (SOL) and extensor digitorum longus (EDL) were isolated under anesthe-sia.The twitch tension, titanic tension and fatigue resistance of SOL and EDL in response to electrical stimulation were measured to reflect the contractile function of the muscles .The copy number ratio of mitochondrial gene cytochrome C oxi-dase subunit I ( COX I) to nuclear gene β-actin was determined to evaluate the mitochondrial biosynthesis .ATP content was measured to mirror mitochondrial function .RESULTS:Compared with control group , CR for 8 weeks significantly in-creased twitch tension and titanic tension of both SOL and EDL , but only improved fatigue resistance in SOL .Markedly in-crease in ATP content in both skeletal muscles by CR intervention was observed , especially in SOL .Although CR activated AMP-activated protein kinase (AMPK) in both 2 muscles, up-regulation of mitochondrial biosynthesis and transcription of mitochondrial regulatory genes peroxisome proliferator-activated receptor γcoactivator 1α( PGC-1α) and nuclear respirato-ry factor ( NRF) was only observed in SOL .CONCLUSION:CR for 8 weeks enhanced the contractility of both rat SOL and EDL in response to electrical stimulation , especially in SOL composed of slow-twitch fibers.The mechanisms may be related to the activation of AMPK and the promotion of mitochondrial biosynthesis in SOL .
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Aim This study was aimed to explore the influence and mechanism of the long-term exercise on skeletal muscle contraction and mitochondrial biosyn-thesis in different muscle fibers.Methods Soleus (SOL)and extensor digitorum longus (EDL)were i-solated from SD male rats with platform running train-ing for eight weeks.The changes of contractility under different electrical stimulation were observed, mito-chondrial biosynthesis,including ATP content,mito-chondrial DNA,the gene expression of PGC-1αand NRF were also detected.Results Long-term endur-ance exercise can improve twitch tension and titanic tension of SOL and EDL ,but only enhanced the fa-tigue resistance in SOL.ATP contents were significant-ly increased in the two types of muscles,but mtDNA content,PGC-1αexpression and NRF translation were only obviously enhanced in SOL,in accompanied with an increase in p-AMPK/AMPK protein ratio.Conclu-sion Long-term endurance exercise increased skeletal muscle contractility and improved the anti-fatigue abili-ty in SOL,which may be associated with increase in mitochondrial biosynthesis via activated AMPK-PGC-1αaxis.
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Objective To investigate the effects of fasting with different time courses on the contraction of skeletal muscle and cardiovascular function in Sprague-Dawley (SD) rats.Methods The healthy and male SD rats were randomly divided into (1) control,(2) 12 h fasting,(3) 24 h fasting,and (4) 48 h fasting groups.After animal models of fasting with different time courses were 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.Langendorff heart perfusion was used to detect some parameters of cardiac function,including left ventricular systolic pressure (LVSP),left ventricular end-diastolic pressure (LVEDP),and maximum ascending and declining rate of left ventricular pressure (± dP/dt max).Then,the heart was suffered from 30 min ischemia followed by 60 min reperfusion,the changes in above cardiac function parameters were recorded again.The contraction response to potassium chloride or phenylephrine and endothelium-dependent relation responses to acetylcholine (ACh) of aortic rings were measured with organ bath.The changes of twitch tension and titanic tension of soleus and EDL were examined to reflect contractive function of skeletal muscle.Results The + dP/dt max was significantly reduced in 24 h and 48 h fasting groups compared to the control (P ＜ 0.01).After ischemia-reperfusion,the heart re-beat time was significantly longer [(24.3 ± 7.0)min vs (14.0 ± 2.9)min,P ＜0.05],both mLVDP and mLVP were significantly higher in 48 h and 24 h fasting groups than control group (P ＜ 0.05),and those changes did not normalized until re-perfusion 60 min.The 48 h fasting increased significantly endothelium-dependent relaxation of aortic rings response to low concentration acetylcholine (P ＜ 0.05),but did not affect the maximum relaxation of aortic rings response to high concentration acetylcholine and contraction of aortic rings responses to potassium chloride and phenylephrine.The 48 h fasting also enhanced significantly titanic tension of soleus compared to the control [(7.01 ± 1.22) N/cm2 vs (5.5 ± 0.75) N/cm2 for48 h-Fasting vs Control,P ＜0.05].Conclusions The 24 ～48 h fasting may induce inhibition of cardiac function,while fasting 48 h can increase the sensitivity of aortic rings responses to ACh and contraction function of soleus in healthy and male rats.
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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.
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Aim Tostudytheeffectof4-phenlybuty-rate acid(4-PBA) on the heart function of diabetic rats and to explore its underlying mechanism. Methods MaleSprague-Dawley(SD)ratsweredividedintothree groups randomly: ( 1 ) control rats;( 2 ) diabetic rats;(3) 4-PBA treated diabetic rats. Type 1 diabetic mod-el was induced by single intraperitoneal injection of strepotozotocin (60 mg·kg-1 ) . After five weeks dia-betic model was established, diabetic rats were treated with 4-PBA by P. O at the dose of 1 g·kg-1 per day for 20 weeks. At the end of the experiment, hemody-namics of the left ventricle and main artery were detec-ted through right carotid artery cannulation in rats. The level of blood glucose, the activity of superoxide dis-mutase( SOD) and nitric oxide synthetase ( NOS) and the content of malondialdehyde ( MDA ) and nitric ox-ide( NO) of serum and myocardial tissue in rats were measuredbycolorimetry.Results Thetreatmentof4-PBA had no effect on blood glucose, the weight of body and heart, but slightly increased systolic and diastolic pressure of artery, heart rate, systolic pressure of left ventricular, maximum increase rate and minimum de-crease rate of left ventricular pressure( ± dp/dt) in di-abetic rats. It also slightly decreased diastolic pressure of left ventricular, shortened diastolic duration of left ventricular ( P > 0. 05 ) . Moreover, it significantly shortened relaxation time of left ventricular in diabetic rats (P<0. 05). In addition, the treatment of 4-PBA obviously enhanced the activity of SOD and NOS, NO content, and reduced the content of MDA in serum and heartofdiabeticrats(P<0.05).Conclusion 4-PBA has a potential protective effect on heart function in diabetic rats, which is achieved by ameliorating he-modynamics and significantly improving diastolic dys-function in diabetic rats. The underlying mechanism may be related to the inhibition of oxidative stress and promoting the genesis of NO in myocardial tissue.
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Objective To investigate the effects of calorie restriction (CR) for 4 weeks on twitch tension,titanic tension,and fatigue contraction induced by electrical stimulation in different kind skeletal muscles from rats and explore the possible mechanisms.Methods The rat model of CR was established by a limitation of 40％ calorie intake of control rats for 4 weeks,and then oral glucose tolerance test (OGTT) was performed.The soleus (SOL) and extensor digitorum longus (EDL) were isolated under anesthetization to detect twitch tension,titanic tension,and fatigue contraction induced by electrical stimulation.Adenosine triphosphate (ATP) content was measured by fluorescent enzymatic methods to reflect mitochondrial function.The ratio of mitochondrial gene COX Ⅰ and nuclear gene β-actin copy number was analyzed to evaluate mitochondrial biogenesis.Furthermore,the transcriptions of peroxisome proliferatoractivated receptor γ coactivator-1 (PGC-1α) and nuclear respiratory factor 1 (NRF1) genes,expressions of phosphorylated adenosine 5'-monophosphate-activated protein kinase (AMPK) and nitric oxide synthase (NOS) proteins,and nitric oxide (NO) content were determined in skeletal muscle.Results The blood glucose level at 30 min and area under the curve of blood glucose levels at various time points during OGTT were significantly decreased in the CR group compared to the control group.The twitch tension [(2.5 ± 0.15)N/cm2 vs (1.24±0.12)N/cm2,(2.66 ±0.21)N/cm2 vs (1.69 ±0.17)N/cm2,P ＜ 0.05],titanic tension [(10.43 ± 0.36) N/cm2 vs (8.06 ± 0.19) N/cm2,(11.35 ± 1.02) N/cm2 vs (8.12 ± 0.23) N/cm2,P ＜ 0.05],and fatigue contraction force in SOL and EDL from CR rats were significantly increased in association with increases of ATP content [(34.82 ±4.31)) mnol/mg protein vs (15.32 ± 1.94) nmol/mg protein,(30.82 ± 2.15) nmol/mg protein vs (12.32 ± 0.97) nmol/mg protein,P ＜ 0.05] and mitochondrial biogenesis (2.75 ± 0.20 vs 1.52 ± 0.06,1.32 ± 0.10 vs 0.84 ± 0.11,P ＜ 0.05) compared to control rats.CR for 4 weeks upregulated the transcriptions of PGC-1α and NRF genes as well as the phosphorylation of AMPK protein in SOL but not in EDL.Furthermore,CR also enhanced NOS expression and NO content in both skeletal muscles.Conclusions CR for 4 weeks can strengthen the contractile function of SOL and DL from rats,and the underlying mechanisms might be related to the upregulation of PGC-1α transcription and AMPK activation,resulting in the enhances of mitochondrial biogenesis and mitochondrial function in skeletal muscles.