模拟失重大鼠心肌与血管组织的热应激诱导HSP70表达

为研究模拟失重是否可以引起大鼠心肌与血管组织HSP70的诱导表达发生改变,用尾部悬吊大鼠模型模拟失重,以研究失重对生理的影响,用Northern杂交与Western印迹分析检测4周模拟失重大鼠热应激后并在室温下恢复1h(SUS-H1)或2h(SUS-H2_心肌,血管组织HSP70表达的变化,结果表明,热应激后,各组大鼠心肌组织的HSP72 mRNA表达的均显著增加,但SUS－H2大鼠心肌组织的表达显著低于CON－H2组;各组大鼠心肌组织HSP72表达也均显著增加,但SUS－H1与SUS－H2大鼠的表达与相应对照组相比,则仅呈降低趋势,其底动脉血管组织的HSP72 mRNA与HSP72诱导表达均显著增高,而在股动脉则两者仅呈降低趋势,上述结果提示,模拟失重可导致大鼠心肌发生类似衰老的心肌改变;身体前,后部血管组织HSP70的诱导表达变化可能与血管的分化性适应方向一致。     

慢性阻断血管紧张素Ⅱ1型受体不能完全防止模拟失重大鼠血管的适应性结构变化

我们以前的工作提示,在模拟失重所引起的血管区域特异性适应变化中,局部肾素．血管紧张素系统（local reninangiotensin system,L-RAS）可能发挥关键调控作用。本文以losartan慢性阻断血管紧张素Ⅱ1型受体（angiotensin Ⅱtypelreceptor,AT1R）,观察模拟失重是否仍能引起血管的这种适应性改变,并检测大血管管壁L-RAS主要成分的表达是否也发生相应变化。以尾部悬吊大鼠模型模拟失重的生理影响。制作基底动脉、胫前动脉、颈总动脉和腹主动脉的HE染色切片,在光学显微镜下进行形态观测：用免疫组织化学技米测量颈总动脉和腹主动脉壁的血管紧张素原（angiotensinogen,AGT）及AT-R的表达变化。结果表明：4周模拟失重引起大鼠基底动脉中膜和颈总动脉管壁各平滑肌肌层肥厚,而胫前动脉和腹主动脉则发生萎缩性改变;给予losartan4周引起上述4种血管皆发生萎缩性变化;阻断AT1R,模拟失重仍然能引起基底动脉、颈总动脉发生相对肥厚性改变和腹主动脉萎缩加重。4周模拟失重还引起颈总动脉壁中AGT和AT1R表达上调,而腹主动脉壁及血管周围组织中AGT和AT1R表达下调;给予losartan4周仅引起腹主动脉壁中AGT和AT1R表达减少;阻断AT1R,模拟失重使腹主动脉壁AT1R表达进一步减少。结果提示,4周模拟失重引起大鼠脑、颈部与后身大、中动脉血管的形态结构改变和L-RAS主要成分表达发生上调或下调,血管L-RAS在其中可能发挥关键性调控作用;但在慢性阻断AT1R的条件下,其它调控机制仍可能在脑血管适应性调节中发挥一定作用。     

失重/模拟失重对内皮细胞的影响实验研究进展

血管内皮作为血管壁的衬里,参与调节组织器官的局部血流和机体其它生理进程,在维持血管完整性和内环境稳定中发挥关键作用。内皮细胞对包括重力在内的机械应力刺激极为敏感,重力变化可对其形态和功能构成不同程度的影响。研究发现,失重/模拟失重通过诱导内皮细胞细胞骨架重塑、质膜caveolae重布,使其合成分泌血管活性物质、炎性介质的能力以及细胞表面粘附分子表达发生改变,这些分子变化又对内皮细胞的生长、增殖、凋亡、迁移和血管生成等具有精细调控作用。本文综合评述了失重/模拟失重对内皮细胞功能的影响,同时围绕文献报道中一些尚存争议的观点进行了适当讨论。     

模拟失重大鼠心肌肌球蛋白重链与肌钙蛋白表达的变化

目前 ,对失重 (微重力 )引起的心脏适应性变化及其在飞行后立位耐力不良发生中的重要意义尚缺乏深刻认识。推测心肌收缩蛋白的改变可能是模拟失重导致心肌收缩性能降低的主要原因之一。本实验的旨在观测中期 (4ＷＫ)模拟失重引起大鼠心肌蛋白含量 ,以及收缩蛋白的主要成份 -肌球蛋白重链 (ＭＨＣ)与肌钙蛋白可能发生的改变 ,籍此阐明模拟失重 4ＷＫ周大鼠心肌收缩性能降低的内在机理。1　材料与方法(1)实验动物分组　雄性ＳＤ大鼠ｌ6只。随机分为对照组 (ＣＯＮ)与悬吊组 (ＳＵＳ) ,每组 8只大鼠。尾部悬吊 4ｗＫ后 ,将大鼠麻醉 ,摘取心脏 ,…     

模拟失重大鼠心肌收缩性能降低涉及细胞钙转运机制

本研究采用离体乳头肌灌流技术,观察了模拟失重４周大鼠大鼠心肌收缩性能的变化。同时采取改变细胞外液中Ｃａ＾２＋浓度,用Ｌａ＾３＋置换细胞膜部位Ｃａ＾２＋,以及快速冷却等干预实验方法,探讨模拟失重大鼠心肌收缩性能发生改变的可能机制。结果表明：模拟失重大鼠乳头肌钙反应的时间明显缩短;冷挛缩实验中的ＥＳＣ／ＲＣＣ６０与ＲＣＣ１／ＲＣＣ６０比值也显著降低。这些均提示模拟失重大鼠心肌收缩性能降低可能与心肌细胞     

失重/模拟失重条件下心肌萎缩的发生机制

心肌能够应对内外环境改变而发生重塑。失重/模拟失重等去负荷条件可导致心肌萎缩、心脏功能下降。从系统和细胞分子层面揭示失重/模拟失重造成心肌萎缩的机制对于航天飞行后心血管功能紊乱的对抗研究至关重要。失重/模拟失重导致机体血流动力负荷下降、代谢需求降低和神经内分泌变化;同时导致包括钙相关信号、NF-κB通路、ERK通路、泛素-蛋白酶体途径以及自噬等通路的改变,上述变化在心肌萎缩的发生发展过程中发挥着关键调控作用。本文从系统和细胞分子层面对失重/模拟失重引起心肌萎缩的发生机制进行综述。     

模拟失重对大鼠腹主动脉L-Arg-NO-cGMP通路的影响

目的:观察尾部悬吊模拟失重对大鼠腹主动脉舒张反应性与一氧化氮合酶表达的影响。方法:体重300~330 g的20只雄性SD大鼠按体重配对随机分为对照组与模拟失重组,模拟失重大鼠采用尾部悬吊方法模拟失重。4周后,利用离体动脉血管环舒张实验与Western blot蛋白免疫印迹方法观察了腹主动脉舒张反应性和腹主动脉一氧化氮合酶eNOS(endothelial NOS)和iNOS(inducible NOS)的表达。结果:悬吊大鼠腹主动脉环对左旋精氨酸(L-Arg)与乙酰胆碱(Ach)的舒张反应显著低于对照,而对硝普钠(SNP)与环磷酸鸟苷(cGMP)的舒张反应在两组间无显著不同。其敏感性在两组间均无显著差别。腹主动脉的eNOS与iNOS表达在模拟失重组与对照组间亦未发现显著差别。结论:本工作提示尾部悬吊模拟失重下大鼠腹主动脉舒张反应的减弱可能是动脉血管内皮功能改变的结果,尤其是NOS活性的变化可能更为重要。     

短期模拟失重可增强大鼠脑动脉平滑肌细胞L-型Ca~(2+)通道对血管紧张素Ⅱ的反应性

已有研究表明模拟失重可引起大鼠脑动脉发生区域特异性变化,其中Ca2+通道和肾素-血管紧张素系统(renin-angio-tensin system,RAS)可能发挥着重要的作用。本研究旨在探讨血管紧张素Ⅱ(angiotensin Ⅱ,Ang Ⅱ)对短期模拟失重大鼠脑基底动脉血管平滑肌细胞(vascular smooth muscle cells,VSMCs)L-型Ca2+通道(L-type calcium channel,CaL)功能的影响。模拟失重(尾部悬吊)3d后,用木瓜蛋白酶法分离大鼠脑基底动脉VSMCs。采用全细胞膜片钳技术,以Ba2+作为载流子,测定CaL电流密度,然后观察Ang Ⅱ对该电流的影响。结果显示,模拟失重3d对大鼠脑基底动脉VSMCs的膜电容和接入电阻无明显影响,但可致VSMCs的CaL电流密度显著增加。不过,模拟失重对CaL的电压激活特性和稳态激活曲线亦无明显影响。对照组和模拟失重组大鼠脑基底动脉VSMCs的CaL电流密度在给予Ang Ⅱ处理后均显著增加,且模拟失重组的增加幅度显著大于对照组。以上结果提示,3d短期模拟失重即可引起大鼠脑动脉VSMCs的CaL发生适应性改变,且可导致其对...     

90d模拟失重大鼠动脉压力反射反应性的改变

本工作研究了90d模拟失重大鼠动脉压力反射反应性的改变。即以血管活性药物变动平均动脉压(MAP),并同时记录反射性心率(HR)变化,采用非线性曲线拟合方法,定量评价清醒大鼠的动脉压力反射反应性的特征参数的改变。同时还利用受体阻断实验,观察迷走和交感神经成分在压力反射活动中的贡献。结果表明:模拟失重大鼠MAP-HR反应曲线向右上方移位,心率低限坪值升高,血压调节范围变窄,静态工作点升高。当心得安阻断β受体后,悬吊组大鼠压力感受性心率反射的平均增益及心率反应范围均高于对照组,提示模拟失重大鼠反射活动中迷走作用增强。     

模拟失重对大鼠心肌力学与生物化学的影响

观察为期４周模拟失重对大鼠心肌收缩性能与收缩蛋白性质的影响,发现模拟失重大鼠左心室乳头肌等长收缩的力学特征发生下列变化：发展张力峰值降低２９％（Ｐ〈０．０１）;达到张力峰值的时间延长１０％（Ｐ〈０．０５）;舒张一半的时间缩短１１％,但未达到显著水平（Ｐ〉０．０５）。心肌力学参数的这些变化表明模拟失重使大鼠心肌收缩性能降低。进一步研究显示,模拟失重大鼠左室心肌肌原纤维Ｃａ＾２＋,Ｍｇ＾２＋－ＡＴＰ酶     

Plasticity of arterial vasculature during simulated weightlessness and its possible role in the genesis of postflight orthostatic intolerance

Even after several decades of extensive research, the basic mechanism of postflight cardiovascular dysfunction has not yet been fully elucidated. It is now well recognized that multiple mechanisms might account for the frequent occurrence of significant postflight orthostatic intolerance. It has been found that all tissues adapt their design when exposed to sustained alteration in local activity and/or stress. The most obvious example is the musculo-skeletal system, structure and function of which might be severely affected during microgravity exposure. In an attempt to elucidate whether structure and function of cardiac and vascular smooth muscle might be affected by simulated by microgravity, a serial work was started several years ago. In this paper, we present our more recent findings on plasticity of arterial vasculature and its innervation state during and after simulated microgravity and its time course.     

Vascular adaptation to microgravity: what have we learned?

Findings from recent bed rest and spaceflight human studies have indicated that the inability to adequately elevate the peripheral resistance and the altered autoregulation of cerebral vasculature are important factors in postflight orthostatic intolerance. Animal studies with rat model have revealed that simulated microgravity may induce upward and downward regulations in the structure, function, and innervation of the cerebral and hindquarter vessels. These findings substantiate in general the hypothesis that microgravity-induced redistribution of transmural pressures and flows across and within the arterial vasculature may well initiate differential adaptations of vessels in different anatomic regions. Understanding of the mechanisms involved in vascular adaptation to microgravity is also important for the development of multisystem countermeasures. However, future studies will be required to further ascertain the peripheral effector mechanism of postflight cardiovascular dysfunction.     

Daily short-period gravitation can prevent functional and structural changes in arteries of simulated microgravity rats.

This study was designed to clarify whether simulated microgravity-induced differential adaptational changes in cerebral and hindlimb arteries could be prevented by daily short-period restoration of the normal distribution of transmural pressure across arterial vasculature by either dorsoventral or footward gravitational loading. Tail suspension (Sus) for 28 days was used to simulate cardiovascular deconditioning due to microgravity. Daily standing (STD) for 1, 2, or 4 h, or +45 degrees head-up tilt (HUT) for 2 or 4 h was used to provide short-period dorsoventral or footward gravitational loading as countermeasure. Functional studies showed that Sus alone induced an enhancement and depression in vasoconstrictor responsiveness of basilar and femoral arterial rings, respectively, as previously reported. These differential functional alterations can be prevented by either of the two kinds of daily gravitational loading treatments. Surprisingly, daily STD for as short as 1 h was sufficient to prevent the differential functional changes that might occur due to Sus alone. In morphological studies, the effectiveness of daily 4-h HUT or 1-h STD in preventing the differential remodeling changes in the structure of basilar and anterior tibial arteries induced by Sus alone was examined by histomorphometry. The results showed that both the hypertrophic and atrophic changes that might occur, respectively, in cerebral and hindlimb arteries due to Sus alone were prevented not only by daily HUT for 4 h but also by daily STD even for 1 h. These data indicate that daily gravitational loading by STD for as short as 1 h is sufficient to prevent differential adaptational changes in function and structure of vessels in different anatomic regions induced by a medium-term simulated microgravity.     

Time course and reversibility of arterial vasoreactivity changes in simulated microgravity rats

Recent works have shown that postflight orthostatic intolerance involves multiple alterations in physiological function during actual or simulated microgravity. In our previous work, we demonstrated that 14-day tail-suspension resulted in an impaired ability of vascular smooth muscle to develop tension in arteries confined to the hindquarter, which have been suggested as an important factor accounting for the occurrence of orthostatic intolerance. To our knowledge, data on arterial vasoreactivity alterations induced by simulated microgravity longer than two weeks are not found. The aim of the present work was to characterize the time course of alterations in vasoconstrictor properties of hindquarter arteries during tail-suspension up to eight weeks, and to examine whether these alterations are reversible.     

Physiology in microgravity.

Studies of physiology in microgravity are remarkably recent, with almost all the data being obtained in the past 40 years. The first human spaceflight did not take place until 1961. Physiological measurements in connection with the early flights were crude, but, in the past 10 years, an enormous amount of new information has been obtained from experiments on Spacelab. The United States and Soviet/Russian programs have pursued different routes. The US has mainly concentrated on relatively short flights but with highly sophisticated equipment such as is available in Spacelab. In contrast, the Soviet/Russian program concentrated on first the Salyut and then the Mir space stations. These had the advantage of providing information about long-term exposure to microgravity, but the degree of sophistication of the measurements in space was less. It is hoped that the International Space Station will combine the best of both approaches. The most important physiological changes caused by microgravity include bone demineralization, skeletal muscle atrophy, vestibular problems causing space motion sickness, cardiovascular problems resulting in postflight orthostatic intolerance, and reductions in plasma volume and red cell mass. Pulmonary function is greatly altered but apparently not seriously impaired. Space exploration is a new frontier with long-term missions to the moon and Mars not far away. Understanding the physiological changes caused by long-duration microgravity remains a daunting challenge.     

Venous distensibility and venous emptying in the legs during a 42-day -6 degrees head-down bedrest

Exposure to actual or simulated microgravity is known to result in changes in lower limb venous compliance or distensibility which may play a role in post-bedrest or postflight orthostatic intolerance. Venous deconditioning has only been described in terms of changes in vascular compliance or distensibility. But a complete understanding of changes in venous hemodynamics and cardiovascular regulation occurring under these conditions has to take into account changes in emptying capacities of the veins which influence venous return, cardiac filling, and cardiac output regulation. Moreover, few data are available about the course of changes in venous hemodynamics for periods of simulated microgravity longer than 4 weeks. The purpose of this investigation was to measure parameters of venous compliance and venous emptying before, during, and after a 42-day period of bedrest at -6 degrees head-down tilt for a better understanding of long term venous physiological adaptation to microgravity.     

Functional alterations in cardiac muscle after medium- or long-term simulated weightlessness and related cellular mechanisms

A serial work on effects of simulated weightlessness on function and structure of cardiac muscle was started in our laboratory several years ago. In our previous papers, a long-term tail-suspension rat model modified by us, and its validity as a simulation of microgravity effects on the cardiovascular system have been reported. In the present paper, we will focus primarily on the nature, time course, and mechanism of functional alterations in rat cardiac muscle during both 4 wk of tail-suspension by our technique and 2 wk of recovery. Besides, some findings concerning changes after 13-wk tail-suspension and the regression during recovery for 3 wk are also included.     

Effect of simulated microgravity on human lymphocytes

During space flight the function of the immune system changes significantly. Several papers reported that postflight the number and the proportion of circulating leukocytes in astronauts are modified (Leach, 1992), the in vitro mitogen induced T cell activation is depressed (Cogoli et al., 1985; Konstantinova et al. 1993) and there are detectable differences in cytokine production of leukocytes as well (Talas et al. 1983; Batkai et al. 1988; Chapes et al. 1992). One of the possible modifying forces is the microgravity condition itself. Our aim was to analyse mechanisms responsible for changing leukocyte functions in low gravity environment. For terrestrial simulation of microgravity we used a Rotary Cell Culture System (RCCS) developed by NASA. We investigated the effect of simulated microgravity on separated human peripheral blood mononuclear cells (PBMCs). We detected the populations of different cells by antibodies conjugated to fluorofors using a Flow Cytometer. Since space flight reduces the number of peripheral blood lymphocytes (Stowe et al., 1999) we supposed that apoptotic (programmed cell death) processes might be involved. This hypothesis was supported by the result of our earlier experiment demonstrating that simulated microgravity increased the level of secreted Tumor Necrosis Factor-alpha (TNFalpha, a known apoptotic signal molecule) significantly (Batkai et al. 1999).     

Dehydrogenase activity in skeletal muscles of rats after long-term exposure to weightlessness

Malate- and isocytratedehydrogenase activity in mitochondrial and cytoplasmic fractions and lactate dehydrogenase activity in hindlimb muscles have been studied at different stages after 18.5-day flight on a biosatellite "Cosmos-1129" and after 20-day hypokinesia. A decrease in dehydrogenase activity has been found on the first postflight day. The enzyme activities returned to the control values in mitochondria, and in the cytoplasm they were greater by day 6 postflight. It was concluded that hypokinesia did not reveal all the effects of microgravity on the whole system but some enzyme alterations in the muscle resembled those observed during the flight. The effects may be caused by the inhibition of both aerobic and anaerobic metabolic pathways under the effect of microgravity.     

Cardiovascular peripheral effector mechanism in postflight orthostatic intolerance: a simulation study

Orthostatic intolerance (OI) following exposure to microgravity or head-down bed rest is frequently observed and is thought to be multifactorial origin. Although hypovolemia is considered as the primary cause of OI, the role played by other factors, such as the lowered vasoconstrictor responsiveness (VCR) of resistance vessels, the enhanced vasoconstriction response of cerebral vessels, and the depressed myocardial contractility need to be elucidated. It is difficult to assess experimentally how each of these changes would affect orthostatic tolerance and how these factors interact with each other. An alternative approach is to conduct simulation studies by use of mathematical models of cardiovascular system (CVS) capable of simulating the CVS response to orthostatic stress. This presentation describes the construction of the model used, and presents the preliminary simulation results illustrating the effects of varying individually the level of hypovolemia, VCR of the resistance vessels in lower limbs and abdominal viscera, VCR of the brain vessels or myocardial contractility on responses to orthostatic stress. The ultimate goal of our work was to integrate the new experimental findings and to simulate the complexity to get a thorough understanding of the mechanism of postflight cardiovascular dysfunction and orthostatic intolerance.