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PubMed1996

[Effects of simulated weightlessness on ultrastructures and oxygen supply and consumption of myocardium in rats].

Weightlessness causes atrophy of myocardium in rats, however, properties of ultra-structural changes and oxygen supply and consumption in myocardium are still unclear. Changes in ultrastructures of left ventricular myocardium in rats tail-suspended for 8W were observed. Qualitative analysis showed that the lysosomes, lipofuscins and degenerate mitochondria increased in myocytes of left ventricle in tail-suspended rats (SUS). The sarcoplasmic reticula were reduced in quantity and shrunken in appearance. The number of extended endothelial projections into the lumen of capillaries increased. Quantitative analysis showed that volume densities of mitochondria and sarcoplasmic reticulum in SUS were reduced by 14.5% and 22.2%, respectively. The number density of mitochondria also had a 12.5% decrease in SUS. The morphometric data-estimated oxygen demand of the myocardium in SUS showed a 16.7% decrease. These results suggested that the feature of the changes be chronic degeneration without the evidence of acute hypoxia in myocardium. The decrease of oxygen consumption of myocardium in SUS didn't cause a reflex reduction in the oxygen supply.

Animals↗
PubMed1999

[Ultrastructural changes of arterial wall from different body parts of rats during simulated weightlessness].

OBJECTIVE: To test the nature of remodeling of arteries in different body parts in adapting to local hemodynamic changes induced by tail-suspension. METHOD: Ultrastructural changes of hindlimb and cerebral arteries from 4-wk tail-suspended (SUS-4), 1-wk recovered (REC-1), and control (CON) rats were studied by transmission electron microscopy. RESULT: For the hindquarter arteries, like the femoral artery and anterior tibial artery, there were fewer smooth muscle layers, less myofilaments in the smooth muscle cell (SMC), and more intercellular substance in SUS-4 group than in CON group. After 1-wk recovery, the internal elastic lamina of the arteries thickened, the amount of myofilaments in SMC increased, the content of intercellular substance restored, and neoformative SMCs emerged under the endothelium. With respect to arteries in the neck region and the brain, like the common carotid artery and basilar artery, SMCs of contractile phenotype were converted to that of synthetic phenotype, and migration and hyperplasia of SMCs also happened. After 1-wk recovery all these alterations were somewhat restored. CONCLUSION: It provided further evidence that peripheral effector mechanism might play an important role in the genesis of postflight orthostatic intolerance.

Actin Cytoskeleton↗
PubMed2002

[Effects of dietary n-3 polyunsaturated fatty acid on lipid metabolism in rats under simulated weightlessness].

Objective. To study the effect of dietary n-3 polyunsaturated fatty acid (PUFA) on the lipid metabolism of tail-suspended rats. Method. 49 male Sprague-Dawley rats were divided into five groups: tail-suspension group I, fed with 10 wt % corn oil, tail-suspension groups II, III, IV were fed with three levels of fish oil (0.5, 1.5 or 3.0 wt %; low, middle and high level of fish oil, respectively). Group V fed with 10 wt % corn oil served as normal control. Result. Viscoelasticity of cell membrane in group III was significantly higher than that of group I (P<0.01); Vascular endothelial cells (VEC) was less in group II compared to group I; Serum total cholesterol (TC) and triglyceride (TG) , serum lipoprotein were lower in groups II, III, IV compared to group I, the higher fish oil content in diet, the lower serum lipid concentration in microgravity. Conclusion. Dietary n-3 PUFA do have distinguished effect on lipid metabolism and n-3 PUFA have certain effects on prevention of atherosclerotic disease and coronary heart disease in rats.

Animals↗
PubMed2003

[Effects of simulated weightlessness on reproduction in male rats].

OBJECTIVE: To study the effects of tail-suspension on gonad and spermatic hormone in male rats. METHOD: After tail-suspension and reambulation some times in male rats, weight of testis was measured, sperm of epididymis was inspected, morphology of testicular cell was compared, and antent of testosterone assay by radioimmunoassay ratio of LH-beta positive cell in pituitary was measured by immunohistochemic. RESULT: After tail-suspension, weight of testis in male rats decreased significantly. Shape of the convoluted tubules and number of all levels of the spermatocyte in testis atrophied markedly. No sperm was found in the epididymis. Content of testosterone decreased markedly. Number of positive cell of beta-subunit of LH in the pituitary increased markedly. CONCLUSION: Tail-suspension has negative effect on sex gland and reproduction function of male rats.

Animals↗
PubMed1995

[Role of the hypophysis, hormonal growth inducers and physical exercises in the regulation of function of thyrocytes, C-cells and parathyrocytes in rats during simulated weightlessness].

Immunohistochemistry and histomorphometry were employed to assay thyroid and parathyroid glands in hypophysectomized rats following a10-day tail suspension in head-down position and daily injection of either physiological solution or growth hormone or insulin-like growth factor 1 on the background of physical exercise, i.e. ascent up a 1 m high staircase with a load fastened to the tail. Hypophysectomy was found to cause atrophic/sclerotic changes in the thyroid and parathyroid glands, and dramatically suppress the functional activity of thyrocytes, C-cells (calcitonin producers) and parathyrocytes (parathormone producers). Assumingly, the impairing effect of hypophysectomy on C-cells and parathyrocytes is consequent to the reduced production of thyroid hormones and concomitant moderation of metabolism. The suspension by tail added somewhat to the severity of changes in thyroid and parathyroid glands under the effect of hypophysectomy, whereas the injection of growth hormone or insulin-like growth factor 1 slightly stimulated thyrocytes, C-cells, and parathyrocytes activities; however, it failed to offset the hypophysectomy-provoked developments. Although the activities of thyrocytes, C-cells or parathyrocytes were not affected by physical exercise, there was a mild C-cell proliferation.

Animals↗
PubMed2005

[Changes of endogenous ouabain in rat serum and certain tissues after exposure to simulated weightlessness].

OBJECTIVE: To investigate the changes of endogenous ouabain (EO) in rat serum and some tissues after exposure to simulated weightlessness and to investigate its possible pathophysiology. METHOD: Male Wistar rats were randomly divided into control group (Con) and 1 week tail-suspension group (TS). Enzyme-linked immunosorbent assay (ELISA) was used to detect the content of EO in serum, hypothalamus, pituitary, adrenal gland, kidney, heart and liver. RESULT: Compared with Con, EO increased significantly in serum, hypothalamus, adrenal gland and kidney after tail suspension (P<0.05). CONCLUSION: Simulated weightlessness induced changes of EO in serum and some tissues, which may have some effects on the regulation of hydro-electrolyte metabolism and cardiovascular functions.

Adrenal Glands↗
PubMed1998

[Effects of hypoxia and qigong on urine malondialdehyde, superoxide dismutase and circulating endothelial cell in humans during simulated weightlessness].

Changes of lipid hyperoxidation and amount of circulating endothelial cells under simulated weightlessness and factors that may influence these changes were observed in 3 groups of subjects (5 in each group) exposed to 17d - 6 degrees head down bed rest (HDBR), HD-BR+ hypoxia and HDBR + qigong respectively. The results showed: (1) simple HDBR promotes antioxidation activity and attenuates hyperoxidation of lipids, and hypoxia and have some influence on the former but not on the latter; (2) circulating endothelial cells decreased significantly after simple HDBR for 7 d but recovered to normal when HDBR continued for 17 d. Hypoxia showed no influence on this effect while Qigong alleviated it significantly. It suggests that (1)both hypoxia and Qigong have some influence on the promotion of antioxidation activity but have no influence on the production of oxygen free radicals. (2) Qigong shows some antagonistic effect against the attenuation of circulating endothelial cells by HDBR.

Bed Rest↗
PubMed1997

Simulated weightlessness to induce chronic hypoactivity of brain norepinephrine for exercise and stress studies.

Although research on the relationship between exercise training and physiological stress reactivity is increasing, we know little about the involvement of brain neurochemistry. Moreover, the few studies that have been performed have concentrated on animals with normally functioning neurochemistry exposed to an acute stressor. Biomedical research is drawing an association between hypoactivation of the physiological stress response and certain medical conditions. As such, there is a need for an animal model that manifests a chronic hypoactivity of the stress system. In this report we describe the results from studies on norepinephrine changes with actual and simulated weightlessness in animals and humans. There is consistent evidence with rats that 14 d of simulated weightlessness produces reduced norepinephrine turnover in selected brainstem nuclei and peripheral tissue mediating the physiological stress response. Little is known about other brain regions, particularly the hypothlamus. These preliminary data suggest that simulated weightlessness is one method by which a chronic hypoactivity of norepinephrine biosynthesis or release might be induced to study exercise training as an intervention.

Adaptation, Physiological↗
PubMed2005

[Effects of simulated weightlessness on ALP, ACP, collagen I, and biomechanics of hind-limb bones in rats].

OBJECTIVE: To investigate effects of 3 weeks simulated weightlessness on biomechanical parameters, alkaline phosphatase (ALP), acid phosphatase (ACP) and collagen I of hind-limb bones in tail-suspended rats. METHOD: Fourteen male SD rats were divided equally into control group (CON) and experimental group; tail-suspended (TS) was used to simulate weightlessness. After 3 weeks tail-suspension, biomechanical parameters of femur were measured; ALP, ACP and collagen I of tibia were observed. RESULT: Elastic load, maximum load, and bending rigidity coefficient decreased significantly (P<0.01), while the maximum deformation and bending toughness coefficient increased markedly (P<0.01 or P<0.05). Morphological results showed that ALP declines significantly in TS group, ACP and type I collagen increased significantly in TS group. CONCLUSION: After tail-suspension for 3 weeks, growth of rat's weight bearing bones are suppressed, biomechanical capability declines, and collagen I metabolism becomes disordered.

Acid Phosphatase↗
PubMed1999

Contributory factors to orthostatic intolerance after simulated weightlessness.

Various factors may contribute to orthostatic intolerance (OI) observed after space flights or simulated weightlessness such as bed rest experiments: individual physical and physiological factors (arterial blood pressure (BP), height), physiological changes induced by real or simulated weightlessness (hypovolaemia, increase in venous distensibility), and space flight or simulation conditions (duration and counter-measure application). Our purpose was to test which of these factors were dominant in contributing to the OI. This was assessed in 47 healthy men participating in bed rest experiments of 4, 14, 28, 30 and 42 days, with or without counter-measures (medical stockings, lower-body negative pressure (LBNP), LBNP + muscular exercise). Nineteen subjects did not finish the orthostatic test (60 degrees head-up tilt or stand test) after bed rest. The occurrence of OI was associated with greater height, low resting BP, greater changes in resting lower-limb venous distensibility throughout the bed rest, and absence of counter-measures.

Adult↗
PubMed2002

Effects of simulated weightlessness on Calbindin D-28K-immunoreactivity in rat soleus muscle spindle.

Objective. To analyze the mechanism involved in muscle spindle deterioration during simulated weightlessness. Method. Using the immunoperoxidase reaction utilizing the ABC (avidin-biotin-complex) method, Calbindin D28K-like immunoreactivity (CaBP-LI) of intrafusal fibres in soleus muscle were detected in 7 d, 14 d tail-suspended rats and compared with control rats. Result. The extrafusal muscle fibres and nerve fibres did not exhibit immunoreactivity to CaBP. CaBP-LI was found in some of the intrafusal muscle fibres in all the muscle spindles. After 14 d suspension, the immunoreactivity to CaBP of the intrafusal fibres decreased markedly. Conclusion. Simulated weightlessness could induce changes in the immunoreactivity of rat soleus muscle spindle to CaBP, which may contribute to the deterioration of muscle spindle.

Animals↗
PubMed2002

[Effects of simulated weightlessness on the expression of cyclooxygenase-2 in rat calvarial osteoblasts induced by fluid shear stress].

OBJECTIVE: To investigate the effect of simulated weightlessness on mechanotransduction in rat calvarial osteoblasts. METHOD: Osteoblasts were isolated from neonatal rat calvariae and then were set to two groups. One was cultured in clinostat to simulate the weightlessness environment. Another was cultured in 1 G gravitational environment. After 60 h, osteoblasts were treated with 0.5 Pa or 1.5 Pa FSS in a flow chamber. The FSS treatment time was set to 30 min and 60 min, respectively. The specimens of each group were obtained for immunohistochemistry staining and determination of expressions of cyclooxygenase-2 (COX-2) in osteoblasts. RESULT: In osteoblasts cultured in 1 G gravitational environment, COX-2 expression was increased remarkably from 30 min to 60 min with the treatment of FSS (P<0.01). There was no clear difference between the expression of COX-2 after treatments of 0.5 Pa or 1.5 Pa FSS; In cells cultured in simulated weightlessness environment, no detectable expression of COX-2 was found with the treatment of 0.5 Pa FSS. The expression of COX-2 was only detected after 60 min treatment of 1.5 Pa FSS, but the level of expression was decreased significantly (P<0.01). CONCLUSION: These results demonstrated that the mechanotransduction in osteoblasts was down-regulated in simulated (correction of stimulated) weightlessness.

Animals↗
PubMed2001

[Daily 1 h standing can prevent depression of myocardial contractility in simulated weightless rats].

Objective. To observe and compare the effect of daily standing of rats for different durations in alleviating the depression of myocardial contractility induced by simulated weightlessness. Method. Fifty male Sprague-Dawley rats were randomly assigned to five groups: simultaneous control (CON), four-week tail-suspension (SUS), SUS plus daily 1 h standing (STD1), SUS plus daily 2 h standing (STD2) and SUS plus daily 4 h standing (STD4). Four weeks later, wet weights of the left soleus, testis and adrenal gland were measured, and the isometric contractile tension and its time parameters of isolated perfused papillary muscles from rats of various groups were examined. Result. Compared with CON, the wet weights of testis in different treatment groups decreased significantly (P<0.05). The wet weight of soleus in SUS decreased by 58.9% (P<0.01); but in STD1, STD2 and STD4, decreased by 38.5%, 24.0% and 11.0% (P<0.01, or P<0.05) respectively. The relative protections were 34.7%, 59.2% and 81.4% (P<0.01) respectively. In SUS group, developed tension (DT), peak rate of tension rise (+dT/dtmax) and peak rate of tension fall (-dT/dtmax) decreased by 32.2%, 29.2% and 30.7% (P<0.05), and time to peak rate of tension rise (TPP) and time to peak tension (TPT) prolonged by 21.2% and 11.0% (P<0.05), respectively. Whereas in STD1, STD2 and STD4, all the parameters reflecting myocardial contractility (like DT, + dT/dtmax, -dT/dtmax and TPP), did not show any significant change as compared with those of CON. However, being an exception, TPT still showed obvious prolongation (P<0.05) in STD1. Conclusion. Daily 1 h standing could prevent depression of myocardial contractility in rat induced by medium-term simulated weightlessness. However, with respect to prevention of atrophic changes in soleus muscle and testis, daily standing for 1 h, 2 h, or 4 h was only partially effective and even totally devoid of any effect, respectively.

Animals↗
PubMed1989

Effect of simulated weightlessness on the response characteristics of human brain.

In order to systematically investigate the effects of simulated weightlessness on the function state of human brain, 15 degrees head-down tilt (HDT) was used to simulate weightlessness, and the response changes of event-related EEG power spectra, medium-frequency synchronous potentials and slow-waves were examined in the present study. It was found that HDT had characteristic effects on the above EEG responses, suggesting that the effects mainly occurred in the brain's regulatory system, therefore, resulting in changes of the brain function state.

Adolescent↗