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。     

Salt-loading and simulated microgravity on baroreflex responsiveness in rats

Cardiovascular adaptations observed during exposure to microgravity results in impairment of baroreflex activity partially as a result of fluid and electrolyte shifts. The head-down tilt rat model mimics some of the physiological observations that have been made in astronauts. We examined the effects of salt-loading on baroreflex activity after 7 day simulated microgravity (30 degrees tail-suspension) and the subsequent 6 hr post-suspension in Sprague-Dawley (SD) rats, using low salt (0.3% NaCl) and high salt (8% NaCl) diets. In suspended animals on a low salt diet, the baroreflex response curve was shifted to the left, while the heart rate (HR) range and MAP50 values were reduced compared to their parallel tethered, non-suspended controls. For non-suspended animals, salt-loading shifted the curve to the right with a reduced HR range. In salt-loaded, suspended animals, the curve and its parameters resemble those of non-suspended animals on a low salt diet. In summary, these data have demonstrated that a short-term (seven days) simulated weightlessness may elicit cardiovascular deconditioning in rats after release from the simulation manifested as an altered responsiveness in baroreceptor-heart rate reflex and a lowered blood pressure while the rats are tethered and horizontal. Our results also suggest the counteracting effect of salt loading on cardiovascular deconditioning.     

Effects of simulated microgravity on immunoreactivity of conjugated-ubiquitin of muscle spindles of soleus in rats

It is well known that the muscle spindle is a receptor of muscle's tension and length, it plays an important role in maintaining the muscle's tension. The aim of the present study is to compare the cross-section area (CSA) and the immunoreactivity of conjugated-ubiquitin in soleus extrafusal and intrafusal fibers after simulated-microgravity in order to demonstrate the role of muscle spindle in muscle atrophy induced by simulated microgravity.     

Effects of simulated microgravity on thyroid carcinoma cells

We aimed to investigate whether simulated microgravity on thyroid carcinoma cells could help to perform in vitro cancer studies such as antitumor drug tests more reliable and to spare animal experiments. We cultured cancer cells at 0 g to enable formation of three-dimensional multicellular tumor spheroids (MCTS), which will resemble the originating tumors. Under microgravity human follicular cells (ML-1 cell line) keep floating with-out stirring so that initial cell-cell interactions required for spheroid formation will be induced by forces due to biochemical components actually expressed on surfaces of cells, whereas gravity related push- or shear events will not influence MCTS formation. Within 12 hours of clinorotation the monolayer turned spontaneously into MCTS with remarkable features: An increase of extracellular matrix proteins and TGF-beta 1. Thyroglobulin, ft3 and ft4 secretion were markedly reduced. These data are in agreement with the observation that astronauts show low thyroid hormone levels after spaceflight.     

Effects of simulated microgravity on embryonic stem cells

There have been many studies on the biological effects of simulated microgravity (SMG) on differentiated cells or adult stem cells. However, there has been no systematic study on the effects of SMG on embryonic stem (ES) cells. In this study, we investigated various effects (including cell proliferation, cell cycle distribution, cell differentiation, cell adhesion, apoptosis, genomic integrity and DNA damage repair) of SMG on mouse embryonic stem (mES) cells. Mouse ES cells cultured under SMG condition had a significantly reduced total cell number compared with cells cultured under 1 g gravity (1G) condition. However, there was no significant difference in cell cycle distribution between SMG and 1G culture conditions, indicating that cell proliferation was not impaired significantly by SMG and was not a major factor contributing to the total cell number reduction. In contrast, a lower adhesion rate cultured under SMG condition contributed to the lower cell number in SMG. Our results also revealed that SMG alone could not induce DNA damage in mES cells while it could affect the repair of radiation-induced DNA lesions of mES cells. Taken together, mES cells were sensitive to SMG and the major alterations in cellular events were cell number expansion, adhesion rate decrease, increased apoptosis and delayed DNA repair progression, which are distinct from the responses of other types of cells to SMG.     

Effects of simulated microgravity conditions on carrageenin-induced oedema in rat

The effects of simulated microgravity conditions, using a three-dimensional clinostat (Random Positioning Machine, RPM), on carrageenin-induced paw oedema in rats as a model of local inflammation were evaluated. RPM-exposed animals showed a significant reduction of oedema and a more pronounced decrease in body weight with respect to control groups. Moreover, aspirine (ASA) treatment, an anti-inflammatory agent, on RPM-exposed rats did not exhibit any activity after carrageenin challenge with respect to RPM control animals on the ground. ASA activity on RPM could be prevented by RPM-induced anti-oedematous effect. RPM-induced anti-oedematous effect did not reversed by pre-treatment with the non-selective glucocorticoid receptor antagonist, mifepristone ruling out the supposed influence of an of cortisol release during the RPM treatment.     

Inhibition of active lymph pump by simulated microgravity in rats

During spaceflight the normal head-to-foot hydrostatic pressure gradients are eliminated and body fluids shift toward the head, resulting in a diminished fluid volume in the legs and an increased fluid volume in the head, neck, and upper extremities. Lymphatic function is important in the maintenance of normal tissue fluid volume, but it is not clear how microgravity influences lymphatic pumping. We performed a detailed evaluation of the influence of simulated microgravity on lymphatic diameter, wall thickness, elastance, tone, and other measures of phasic contractility in isolated lymphatics. Head-down tail suspension (HDT) rats were used to simulate the effects of microgravity. Animals were exposed to HDT for 2 wk, after which data were collected and compared with the control non-HDT group. Lymphatics from four regional lymphatic beds (thoracic duct, cervical, mesenteric, and femoral lymphatics) were isolated, cannulated, and pressurized. Input and output pressures were adjusted to apply a range of transmural pressures and flows to the lymphatics. Simulated microgravity caused a potent inhibition of pressure/stretch-stimulated pumping in all four groups of lymphatics. The greatest inhibition was found in cervical lymphatics. These findings presumably are correlated to the cephalic fluid shifts that occur in HDT rats as well as those observed during spaceflight. Flow-dependent pump inhibition was increased after HDT, especially in the thoracic duct. Mesenteric lymphatics were less strongly influenced by HDT, which may support the idea that lymph hydrodynamic conditions in the mesenteric lymphatic during HDT are not dramatically altered.     

Influence of simulated microgravity on human skeletal muscle architecture and function

Ten male volunteers underwent a period of prolonged bed rest. Four subjects performed exercise countermeasures 2-3 times per week, while 6 subjects received no countermeasures. After bed rest plantarflexor force declined significantly (P < 0.001) in both exercise (-42%) and control (-55%) groups. The internal architecture of the gastrocnemius medialis (GM) muscle was significantly altered. This was associated with a reduction in fascicle shortening during isometric contraction. Exercise countermeasures partially mitigated the loss of muscle force and function following 90 days of bed rest.     

Effects of a simulated microgravity model on cell structure and function in rat testis and epididymis.

A tail-suspension (TS) rat model used to simulate microgravity was tested for its effects on the anatomy, cell structure, and function of the testis and epididymis in sexually mature male rats. Rats suspended for 7 days without inguinal canal ligation exhibited a significant (P less than or equal to 0.05) reduction in testis weight compared with controls (1.55 +/- 0.04 to 1.1 +/- 0.02 g). Except for the liver, epididymis, and adrenals of TS rats and TS rats allowed to recover for 7 days, no significant (P less than or equal to 0.05) change was observed in the weight of other body and accessory sex organs. A histological examination of the testes and epididymides of model animals revealed disorganized seminiferous tubules and accumulation of large multinucleated cells and spermatids in the lumen of the epididymis. A significant (P less than or equal to 0.05) increase in serum luteinizing hormone (53.1 +/- 6.7 to 66.2 +/- 10.1 ng/ml) and follicle-stimulating hormone (257 +/- 25 to 305 +/- 38 ng/ml) was observed in TS nonligated rats, whereas serum prolactin and testosterone levels were observed to decline from 8.3 +/- 1.3 to 5.1 +/- 0.29 and 7.1 +/- 1.3 to 3.8 +/- 0.25 ng/ml, respectively. Decreases in testis protein content and testosterone levels of the testis, interstitial fluid, and epididymis were also observed in model animals. These data demonstrate that the suspension procedure used in the National Aeronautics and Space Administration TS model results in the testis and epididymis translocating into the abdominal cavity, causing cellular degeneration and organ dysfunction.     

Effects of 30 day simulated microgravity and recovery on fluid homeostasis and renal function in the rat

Transition from a normal gravitational environment to that of microgravity eventually results in decreased plasma and blood volumes, increasing with duration of exposure to microgravity. This loss of vascular fluid is presumably due to negative fluid and electrolyte balance and most likely contributes to the orthostatic intolerance associated with the return to gravity. The decrease in plasma volume is presumed to be a reflection of a concurrent decrease in extracellular fluid volume with maintenance of normal plasma-interstitial fluid balance. In addition, the specific alterations in renal function contributing to these changes in fluid and electrolyte homeostasis are potentially responding to neuro-humoral signals that are not consistent with systemic fluid volume status. We have previously demonstrated an early increase in both glomerular filtration rate and extracellular fluid volume and that this decreases towards control values by 7 days of simulated microgravity. However, longer duration studies relating these changes to plasma volume alterations and the response to return to orthostasis have not been fully addressed. Male Wistar rats were chronically cannulated, submitted to 30 days head-down tilt (HDT) and followed for 7 days after return to orthostasis from HDT. Measurements of renal function and extracellular and blood volumes were performed in the awake rat.     

Effects of microgravity on vestibular development and function in rats: genetics and environment

Our anatomical and behavioral studies of embryonic rats that developed in microgravity suggest that the vestibular sensory system, like the visual system, has genetically mediated processes of development that establish crude connections between the periphery and the brain. Environmental stimuli also regulate connection formation including terminal branch formation and fine-tuning of synaptic contacts. Axons of vestibular sensory neurons from gravistatic as well as linear acceleration receptors reach their targets in both microgravity and normal gravity, suggesting that this is a genetically regulated component of development. However, microgravity exposure delays the development of terminal branches and synapses in gravistatic but not linear acceleration-sensitive neurons and also produces behavioral changes. These latter changes reflect environmentally controlled processes of development.     

Rat muscle plasticity in response to simulated or real microgravity

Data concerning muscle plasticity in real or simulated microgravity is discussed. Possible mechanisms responsible for the muscular atrophy associated with microgravity are explored, including changes in muscle protein synthesis, fast- and slow-twitch fiber specific changes, various metabolic alterations, blood supply and other factors. The authors conclude that a combination of local and systemic factors are responsible for the observed changes in muscle physiology.     

Influence of simulated microgravity on the exercise performance of Fischer 344 rats

Measurements from mission specialists after space flights or from subjects subjected to head down tilt experiments have demonstrated a decrease in exercise performance. Similar decreases have been reported for rats that have participated in simulated microgravity studies using the head down-tail suspended method of Morey-Holton (HDS). Because it is unclear whether older animal populations would exhibit similar responses, we undertook a HDS study with Fischer 344 male rats.     

模拟失重对白假丝酵母菌增殖和毒性的影响

【背景】近年来研究发现,失重条件可对一些致病微生物的增殖和毒性产生影响,白假丝酵母菌(Candida albicans)是典型的条件性致病真菌,在太空环境和人体中普遍存在,研究失重条件下白假丝酵母菌的增殖和毒性意义重大。【目的】利用旋转细胞培养系统(Rotary cell culture system,RCCS)模拟失重环境对白假丝酵母菌进行连续传代培养,检测模拟失重环境对白假丝酵母菌增殖情况、毒性以及基因表达的变化。【方法】将白假丝酵母菌接种在旋转生物反应器(High aspect rotating vessel,HARV)中,利用旋转细胞培养系统连续传代培养14 d,然后对菌株进行增殖速率测定、不同pH条件下增殖能力测定、生物膜相对形成能力测定和细胞毒性和动物毒力测定;利用转录组测序技术找出差异表达基因,结合性状分析模拟失重可能对白假丝酵母菌增殖和毒力的影响。【结果】与对照组相比,模拟失重组白假丝酵母菌对数期提前,增殖速率加快,在适宜pH条件下的增殖能力普遍提高,但其生物膜形成能力相对减弱,对LoVo细胞和小鼠的毒性减弱;转录组测序发现,模拟失重组共有280个基因表达差异达1.5倍以上(P0.05),其中248个上调、32个下调。差异基因经基因功能注释(Gene ontology,GO)和京都基因及基因组百科全书(Kyoto encyclopedia of genes and genomes,KEGG)富集分析发现,相关胞膜形成及细胞分裂基因表达上调,生物膜形成、细胞黏附及共生粘连宿主基因表达下调。【结论】模拟失重环境可引起白假丝酵母菌增殖和毒性水平发生变化,相关改变可为研究失重环境对微生物的影响提供参考。     

Effects of simulated microgravity (HDT) on blood fluidity.

Exposures to microgravity and head-down tilt (HDT) produce similar changes in body fluid. This causes an increase in hematocrit that significantly affects hemorheological values. Lack of physical stimulation under bed rest conditions and the relative immobility of the crew during spaceflight also affects the blood fluidity. A group of six healthy male subjects participated as volunteers, and blood samples were collected 10 days before, on day 2 and day 9, and 2 days after the HDT phase. Blood rheology was quantified by plasma viscometry, red cell aggregability, and red cell deformability. A reduced red cell deformability, an indication of the diminished quality of the red blood cells, was measured under HDT conditions that finally led to the so-called "space flight anemia." Enhanced red cell membrane fragility induced by diminished physical activity and an increase in hemoglobin concentration are responsible for this effect. Plasma viscosity is reduced as a result of diminished plasma proteins. However, despite the reduction in plasma proteins, including fibrinogen, alpha 2-macroglobulin, and immunoglobulin M, red cell aggregation was enhanced, principally because of the increase in hematocrit. Our results of hemorheological alterations under HDT conditions may help to elucidate the formerly documented hematologic changes during spaceflight.     

Effects of simulated microgravity on DU 145 human prostate carcinoma cells

The high aspect rotating-wall vessel (HARV) was recently designed by NASA to cultivate animal cells in an environment that simulates microgravity. This work examines the effects of HARV cultivation on DU 145 human prostate carcinoma cells. In the HARV, these prostate cells grew in suspension on Cytodex-3 microcarrier beads to form bead aggregates with extensive three-dimensional growth between beads and on the aggregate surface. HARV and spinner-flask control cultures of DU 145 cells had similar doubling times, but the former was characterized by a higher percentage of G(1)-phase cells, larger bead aggregates, enhanced development of filopodia and microvilli-like structures on the aggregate surface, and stronger staining for select cytoskeletal proteins (cytokeratins 8 and 18, actin, and vimentin). When compared with static controls grown in a T-flask and Transwell insert, HARV cultures grew more slowly and differences in the cell cycle and immunostaining became more pronounced. These results suggest that HARV cultivation produced a culture that was less aggressive from the perspective of proliferation, more differentiated and less pliant than any of the three control cultures examined in this work. Possible factors effecting this change are discussed including turbulence and three-dimensional growth. (c) 1996 John Wiley & Sons, Inc.     

Effects of ligation of the ductuli efferentes or the epididymis on testicular function and secretion of gonadotropins in rats]

One week after ligating the vasa efferentes or the corpus epididymis in adult Wistar rats, we have studied the histological structure of the testes, measured their weights, as well as those of the seminal vesicles, and estimated F.S.H. and I.C.S.H. levels in the plasma through radioimmunoassay. Whereas ligating the corpus epididymis has not effect, ligating the efferent ducts damages the germinal line, without any damage on the Leydig cells; it also raises F.S.H. circulating level, if not I.C.S.H. level. We therefore confirm an inhibin production by seminiferous tubules, this hormone returning to the blood stream in the testis or rather in the head of epididymis as our research in progress suggests.     

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.     

模拟高原低压低氧环境对大鼠心脏结构和功能影响*

目的: 探讨模拟海拔7 000 m低压低氧环境对大鼠心脏结构和功能的影响。方法: 96只雄性SD大鼠随机分为常压常氧对照组(对照组)和高原低压低氧组(低氧组)。低氧组大鼠放置于大型多因素复合环境模拟实验舱内,模拟海拔7 000 m高原环境饲养。实验舱运行时间23 h/d,控制昼夜比大约12 h∶12 h;对照组置于相同条件的常压常氧环境下饲养。低氧组又根据低氧时间不同分为3 d组、7 d组、14 d组和28 d组,同时设置与各低氧组相对应的对照组,每组均12只大鼠。应用超声心动图、心电图、血常规、血生化综合评价高原低压低氧环境下大鼠心脏结构和功能变化,心肌组织HE染色分析心肌组织病理变化。结果: 与相同时间点对照组比较①随着低压低氧暴露时间延长,大鼠体质量增长明显缓慢,动脉血氧饱和度14 d和28 d显著降低(P＜0.05)。②低氧组大鼠左心室舒张末期前壁厚度(LVAWD)及左心室舒张末期后壁厚度(LVPWD)于28 d时显著升高(P＜0.05)。舒张末期左心室腔直径(LVIDD)及收缩末期左心室腔直径(LVIDS)于28 d时明显降低(P＜0.05,P＜0.01)。左心室射血分数(EF%)、左室短轴缩短率(FS%)、肺静脉血流峰值速度(PV peak velocity)及肺静脉血流峰梯度(PV peak gradient)于低氧7 d 下降明显(P＜0.05,P＜0.01),低氧14 d 及低氧28 d 恢复。③低氧组大鼠心电图QRS间期与QT间期在14 d 及28 d 显著延长(P＜0.05,P＜0.01)。ST段3 d和7 d显著压低(P＜0.05,P＜0.01)。R波振幅于 7 d、14 d 及28 d 显著降低(P＜0.05,P＜0.01)。④低氧各组大鼠红细胞计数(RBC)、血红蛋白(HGB)、红细胞分布宽度(RDW)均明显升高(P＜0.01)。血小板计数(PLT)于14 d 及28 d 明显下降(P＜0.01)。血肌酐(CR)于14 d及28 d显著升高(P＜0.05)。⑤心肌病理提示,低氧3 d 和7 d 可见心肌水肿、肌浆凝聚,横纹不清,灶状变性和坏死伴炎性细胞浸润。低氧14 d 和28 d 心肌组织炎症性病理损伤逐渐减少。心肌细胞逐渐肥大,成纤维细胞逐渐增生。心肌间质胶原纤维逐渐增多等心肌代偿修复性病理变化显著。结论: 暴露于模拟海拔7 000 m低压低氧环境下3 d大鼠心功能明显降低,7 d最为显著。