Effects of repeated bouts of squatting exercise on sub-maximal endurance running performance

It is well established that exercise-induced muscle damage (EIMD) has a detrimental effect on endurance exercise performed in the days that follow. However, it is unknown whether such effects remain after a repeated bout of EIMD. Therefore, the purpose of this study was to examine the effects of repeated bouts of muscle-damaging exercise on sub-maximal running exercise. Nine male participants completed baseline measurements associated with a sub-maximal running bout at lactate turn point. These measurements were repeated 24–48 h after EIMD, comprising 100 squats (10 sets of 10 at 80 % body mass). Two weeks later, when symptoms from the first bout of EIMD had dissipated, all procedures performed at baseline were repeated. Results revealed significant increases in muscle soreness and creatine kinase activity and decreases in peak knee extensor torque and vertical jump performance at 24–48 h after the initial bout of EIMD. However, after the repeated bout, symptoms of EIMD were reduced from baseline at 24–48 h. Significant increases in oxygen uptake $ (\dot{V}{\text{O}}_{2} ) $ , minute ventilation $ (\dot{V}_{\text{E}} ) $ , blood lactate ([BLa]), rating of perceived exertion (RPE), stride frequency and decreases in stride length were observed during sub-maximal running at 24–48 h following the initial bout of EIMD. However, following the repeated bout of EIMD, $ \dot{V}{\text{O}}_{2} ,\;\dot{V}_{\text{E}} , $ [BLa], RPE and stride pattern responses during sub-maximal running remained unchanged from baseline at all time points. These findings confirm that a single resistance session protects skeletal muscle against the detrimental effects of EIMD on sub-maximal running endurance exercise.     

Relationship between oxygen uptake kinetics and performance in repeated running sprints

The purpose of this study was to test the hypothesis that subjects having a shorter time constant for the fast component of kinetics in a transition from rest to constant exercise would maintain their speed for a longer time during repeated sprint exercise (RSE). Eleven male soccer players completed a graded test, two constant exercises at 60% maximal aerobic speed and RSE, consisting of fifteen 40-m sprints alternated with 25 s of active recovery. All the tests were performed on the field (200 m indoor track). The parameters of the kinetics (time delay, time constant, and amplitude of the primary phase) during the two constant exercises were modeled. All subjects elicited during the RSE. A significant correlation was found between and the relative decrease in speed during the 15 sprints (r=0.71; p < 0.05), but not between and the cumulated time for the 15 sprints (r=0.48; p > 0.05). There were significant correlations between the time constant of the primary phase and the relative decrease in speed during the 15 sprints (r=0.80; p < 0.01) and the cumulated time for the 15 sprints (r=0.80; p < 0.01). These results suggest that individuals with faster kinetics during constant load exercise might also have a faster adjustment of during RSE leading to a shorter cumulated time and a lower relative decrease in speed during the 15 sprints.     

Effects of 8 weeks of CPAP on lipid‐based oxidative markers in obstructive sleep apnea: a randomized trial

Dyslipidaemia and increased oxidative stress have been reported in severe obstructive sleep apnea, and both may be related to the development of cardiovascular disease. We have previously shown in a randomized crossover study in patients with moderate to severe obstructive sleep apnea that therapeutic continuous positive airway pressure treatment for 8 weeks improved postprandial triglycerides and total cholesterol when compared with sham continuous positive airway pressure. From this study we have now compared the effect of 8 weeks of therapeutic continuous positive airway pressure and sham continuous positive airway pressure on oxidative lipid damage and plasma lipophilic antioxidant levels. Unesterified cholesterol, esterified unsaturated fatty acids (cholesteryl linoleate: C18:2; and cholesteryl arachidonate: C20:4; the major unsaturated and oxidizable lipids in low‐density lipoproteins), their corresponding oxidized products [cholesteryl ester‐derived lipid hydroperoxides and hydroxides (CE‐O(O)H)] and antioxidant vitamin E were assessed at 20:30 hours before sleep, and at 06:00 and 08:30 hours after sleep. Amongst the 29 patients completing the study, three had incomplete or missing [CE‐O(O)H] data. The mean apnea –hypopnoea index, age and body mass index were 38 per hour, 49 years and 32 kg m^?2, respectively. No differences in lipid‐based oxidative markers or lipophilic antioxidant levels were observed between the continuous positive airway pressure and sham continuous positive airway pressure arms at any of the three time‐points [unesterified cholesterol 0.01 mm , P > 0.05; cholesteryl linoleate: C18:2 0.05 mm , P > 0.05; cholesteryl arachidonate: C20:4 0.02 mm , P = 0.05; CE‐O(O)H 2.5 nm , P > 0.05; and lipid‐soluble antioxidant vitamin E 0.03 μm , P > 0.05]. In this study, accumulating CE‐O(O)H, a marker of lipid oxidation, does not appear to play a role in oxidative stress in obstructive sleep apnea.     

Thioredoxin regulation of ischemic preconditioning

Thioredoxins are a class of small redox-regulating proteins that appear to play a crucial role in many oxidative stress-inducible degenerative diseases. A recent study demonstrated a reduction of thioredoxin-1 (Trx1) protein in the ischemic reperfused myocardium. When the same heart was adapted to ischemic stress by preconditioning with repeated cyclic episodes of small duration of ischemia and reperfusion, there was an increased induction of Trx1 expression. Inhibition of Trx1 expression resulted in reduced postischemic ventricular recovery and increased myocardial infarct size in the preconditioned heart. Corroborating these findings, transgenic mouse hearts overexpressing Trx1 were resistant to ischemic reperfusion injury as compared with the hearts from wild-type mice. Thus, it appears that thioredoxin plays a crucial role in cardioprotection induced by preconditioning.     

The effects of ischemic preconditioning on aerobic and anaerobic variables associated with submaximal cycling performance

Acute limb ischemia induced by pressure cuffs before activity (ischemic preconditioning; IPC) has been reported to improve exercise performance at maximal efforts. The purpose of this investigation was to determine the effects of IPC during a submaximal performance test in competitive amateur level cyclists. Twelve healthy, male cyclists participated in two performance tests in which they cycled at successive relative intensities of 30, 50, and 70% of their maximal power output for 5 min each. The test culminated with an intensity of 90% of their maximal power output until exhaustion. Prior to each test, subjects randomly completed a control (CON) or IPC treatment. The IPC treatment consisted of alternating 220 mmHg of pressure applied by a cuff to the proximal portion of both thighs for 3, 5 min bouts separated by 5 min of rest. In addition to performance time to exhaustion, variables associated with aerobic performance (oxygen consumption, ventilation, respiratory exchange ratio, heart rate, and blood lactate) were measured continuously throughout the performance test. Statistical comparisons of data were made with repeated measures analyses of variance or paired T tests and significance was accepted as P < 0.05. Heart rate at the 30% relative intensity was significantly higher for the IPC treatment, but there were no other statistically significant differences between the control and IPC treatments across all variables and relative intensities. In this group of competitive amateur-level cyclists, an acute treatment of IPC did not improve performance at each submaximal intensity or increase time to exhaustion.     

血清白细胞介素8和白细胞介素10在心肌缺血预处理中的变化及意义

目的: 探讨缺血预处理(IP)对心肌细胞的保护机制。方法: 收集2004年4月-12月期间36例在我科行瓣膜置换手术的病人资料,根据是否采取缺血预处理分为预处理组(IP,20例)和对照组(control,16例),比较2组炎症因子白细胞介素-8(IL-8)、白细胞介素-10(IL-10)和心肌细胞Bcl-2、caspase-3的变化情况,分析IP对机体炎症反应的影响。结果: 2组病人细胞因子IL-8、IL-10均在主动脉开放6h时达到高峰,术后5 d均恢复到术前水平。预处理组开放后6 h、术后1 d、术后2 d IL-8水平明显低于对照组(P<0.05),IL-10水平显著高于对照组(P<0.05)。复灌后对照组心肌细胞Bcl-2蛋白表达轻度提高,与阻断前比较,无差异;而复灌后IP组心肌细胞Bcl-2蛋白表达明显提高,与阻断前和对照组比较,差异显著(P<0.05);并与IL-10呈正相关性,与IL-8呈负相关性。对照组复灌后心肌细胞caspase-3蛋白表达显著提高,IP组心肌细胞中caspase-3蛋白表达也增高,但比对照组降低,2组间有显著差异(P<0.05)。结论: 缺血预处理可能通过降低机体的炎症反应途径达到心肌细胞保护的效果。     

非创伤缺血预处理对大鼠缺血再灌注心肌的作用

目的:确定非创伤性缺血预处理对大鼠缺血/再灌注(I/R)心肌损伤是否具有对抗作用,以扩展缺血预处理的实际应用.方法:采用非创伤性下肢缺血预处理及经典缺血预处理的动物模型,比较两种处理方法对I/R心肌损伤的效应.实验动物分4组:正常对照组(NC,n=8),开胸旷置50 min;缺血/再灌注组(I/R,n=12),结扎冠脉30 min,再灌注20、180 min;经典缺血预处理组(C-IPC,n=12),按经典Murry法复制;非创伤性下肢缺血预处理组(N-WIPC,n=12),捆绑双下肢5 min,松开5 min,反复4次后,阻断冠脉30 min,再灌20、180 min.以左室功能,心肌梗塞范围,血清肌酸激酶(CK)及心肌组织丙二醛(MDA)含量、超氧化物歧化酶(SOD)活性为观察指标.结果:与I/R组相比,N-WIPC组与C-IPC组均显著缩小I/R后的心肌梗塞范围(P＜0.01);明显恢复I/R后的左室功能(P＜0.05,0.01);减轻自由基对心肌的损害:血清CK,心肌MDA含量显著降低(P＜0.01).N-WIPC组还使心肌SOD活性增高(P＜0.05).结论:非创伤性下肢缺血预处理与经典缺血预处理可诱发同等强度的心肌预处理效应.     

缺血预处理的抗心律失常作用

应用离体大鼠心脏Ｌａｎｇｅｎｄｏｒｆｆ灌流全心缺血模型，研究缺血预处理的抗收律失常作用及其作用的持续时间。发现ＩＰ可降低自搏心脏和人工起搏心脏的心率失常发生及严重程度，并引起心室颤动阈的升高；ＩＰ对随后的缺血－再灌过程中室性频率的改变无改善作用。     

肿瘤坏死因子-α预处理与缺血预处理在减轻肝脏缺血再灌注损伤的作用

目的研究采用肿效瘤坏死因子-α(TNF-α)预处理与采用缺血预处理两种方法对减轻大鼠肝脏缺血再灌注损伤(IRI)的作用效果,并探讨采用TNF-α预处理减轻大鼠肝脏IRI的机制。方法将40只Wistar大鼠随机分为4组:假手术组(SO组)仅行开腹及游离肝十二指肠韧带;缺血再灌注组(IR组)采用Pringle’s法阻断肝门30 min,再灌注6 h;缺血预处理组(IPC组)采用Pringle’s法阻断肝门10 min,开放血流10 min,此后操作同IR组;TNF-α预处理组(TPC组),术前30 min给予TNF-α1μg/kg腹腔注射,此后操作同IR组。检测血清谷丙转氨酶(ALT)和谷草转氨酶(AST),采用免疫组织化学检测Bcl-2蛋白和NF-κB p65蛋白表达情况,以及肝细胞凋亡指数(AI)。结果 IPC组血清ALT、AST水平为(316.4±90.6)U/L、(316.4±90.6)U/L,TPC组为(336.8±79.4)U/L、(392.7±109.3)U/L,与IR组(642.8±149.3)U/L、(730.6±103.0)U/L比较明显降低,P0.05差异有统计学意义;肝细胞凋亡评分AI在IPC组(4.36+0.88)和TPC组(4.94+2.04)明显降低,与IR组(9.48+2.42)比较,P0.05差异有统计学意义;肝组织内Bcl-2蛋白阳性表达在IPC组(62.30+9.20)和TPC组(60.99+6.30)升高,与IR组(11.45+11.97)比较,有显著性差异(P0.05);NF-κB p65阳性表达在IPC组(31.56+4.85)和TPC组(32.80+5.30)明显降低,与IR组(68.33+6.07)比较,有显著性差异(P0.05)。上述各项指标在IPC组与TPC组间,差异无统计学意义(P0.05)。结论采用TNF-α预处理与缺血预处理对减轻大鼠肝脏IRI的效果一致,TNF-α预处理通过抑制NF-κB p65蛋白表达、激活凋亡抑制基因Bcl-2蛋白表达,减轻了大鼠肝脏IRI。     

缺血预处理联合缺血后处理对肺移植中缺血再灌注肺损伤的影响

背景：研究显示缺血预处理和缺血后处理在缺血再灌注肺损伤中均具有明显的保护作用。 目的：观察缺血预处理联合缺血后处理对肺移植中缺血再灌注损伤的累积保护效应。 方法：将40只SD大鼠随机等分为假手术组、模型组、缺血预处理组、缺血后处理组和联合处理组。后4组建立缺血再灌注肺损伤动物模型,缺血预处理组、缺血后处理组和联合处理组在造模前或/和造模后反复3次阻断开放左侧肺门。 结果与结论：与缺血预处理组和缺血后处理组相比,联合处理组大鼠肺组织的干质量比、丙二醛和髓过氧化物酶降低(P < 0.05),而肺组织中超氧化物歧化酶活性升高(P < 0.05),肺组织病理损伤程度明显减轻;缺血预处理组与缺血后处理组大鼠肺组织超氧化物歧化酶活性、丙二醛水平及髓过氧化物酶活性接近(P > 0.05),且肺组织病理损伤程度基本相似。而且缺血预处理与联合处理组中超氧化物歧化酶、丙二醛和髓过氧化物酶水平呈正相关。提示缺血预处理和缺血后处理联合应用对于减轻中性粒细胞的侵润和激活及氧化反应对于肺组织的损伤有明显的累积保护效应,从而可以更好的减轻肺缺血再灌注损伤程度。     

Trigger mechanism of neuroprotective effect of ischemic preconditioning

Analysis of literature data indicates that adenosine, glutamate, NO, reactive oxygen species, erythropoietin, interleukin-1 are triggers of delayed preconditioning of brain. The issue of involvement of bradykinin, opioids, TNF-alpha in preconditioning remains unclear, although possibility of these compounds to induce a state of increased tolerance to ischemia does not induce a doubt. It was established that adenosine receptor agonists, bradykinin, opioids, NO* donors can mimic a phenomenon of early preconditioning.     

去甲肾上腺素和缺血预处理对大鼠缺血再灌注心肌细胞凋亡、Bcl-2、Bax蛋白表达的影响

目的:研究去甲肾上腺素预处理(NE-P)和缺血预处理(IP)对大鼠缺血再灌注(I/R)心肌细胞凋亡及相关基因Bcl-2和Bax蛋白表达的影响。方法:复制缺血再灌注损伤(IRI),采用末端标记技术(TUNEL)检测心肌细胞凋亡;应用免疫组化SABC法检测Bcl-2和Bax蛋白表达。结果:I/R组凋亡细胞较多,NE-P组及IP组凋亡细胞明显少于I/R组(P＜0.01)。在I/R组Bcl-2的表达少而Bax的表达较多,NE-P组及IP组Bcl-2的表达明显高于I/R组(P＜0.01),而Bax的表达明显低于I/R组(P＜0.01)。NE-P组与IP组各指标均无显著差异(P＞0.05)。结论:NE-P可抑制I/R诱发的心肌细胞凋亡,Bcl-2和Bax的蛋白表达在心肌凋亡的发生中起重要作用。NE-P与IP两者对心肌细胞凋亡及相关基因表达的影响的作用相近。     

金属硫蛋白在大鼠缺血预处理中的变化

目的：探讨大鼠心脏缺血预处理（IPC）中金属硫蛋白（MT）的变化。方法：采用经典的IPC模型，与I/R心肌损伤比较。实验动物分为3组：假手术组（n=6），开胸旷置2 h 20 min；缺血/再灌注组（n=12），结扎左冠状动脉前降支40 min，再灌注1 h 40 min；经典IPC组（n=12），按经典的Murry法复制。以心肌MT的含量，心肌梗塞范围，心肌组织丙二醛（MDA）含量和超氧化物歧化酶（SOD）活性为观察指标。结果：IPC组心肌MT含量明显高于I/R组（P<0.01），心肌MDA含量明显低于I/R组（P<0.01），心肌SOD活性明显高于I/R组（P<0.01）。经直线相关分析，IPC组心肌MT含量与SOD活性呈正相关（r=0.91, P<0.01），与MDA含量呈负相关（r=-0.92, P<0.01），IPC组心肌梗塞范围明显小于I/R组（P<0.05）。结论：缺血预处理能促进大鼠心肌MT合成，MT可能参与IPC的保护效应。     

缺血预处理对肺再灌注损伤脂质过氧化的影响

目的：观察缺血预处理对在体兔肺常温缺血再灌注损伤脂质过氧化的影响。方法：采用阻断左肺门的肺缺血再灌注损伤模型。硫代巴比妥酸法及UFN13直接法测肺组织丙二醛（MDA）、超氧化物歧化酶（SOD）、谷航甘肽过氧化物酶（GSHpx)及肺组织光镜观察。结果：缺血再灌组左肺MDA较假手术组和缺血组为高,而SOD和GSHpx活性较低（P＜0．01）,肺组织损伤较重。与缺血再灌组比较,缺血预处理 缺血再灌组有较低的MDA含量和较高的SOD与GSHpx活性（P＜0．05）,肺损伤亦较轻。结论：缺血预处理可减轻兔肺常温缺血再灌注诱导的脂质过氧化反应。