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PubMed1992

Understanding the organization of the amphibian egg cytoplasm: gravitational force as a probe.

A combination of hypergravity (centrifugation) and hypogravity (clinostat) studies have been carried out on amphibian (frog, Xenopus) eggs. The results reveal that the twinning caused by centrifugation exhibits substantial spawning to spawning variation. That variation can be attributed to the apparent viscosity of the egg's internal cytoplasm. Simulated hypogravity results in a relocation of the egg's third (horizontal) cleavage furrow, towards the equator. Substantial egg-to-egg variation is also observed in this "cleavage effect". For interpreting spaceflight data and for using G-forces as probes for understanding the egg's architecture the egg variation documented herein should be considered.

Animals↗
PubMed1999

Growth of Prunus tree stems under simulated microgravity conditions.

Stem growth of Prunus trees under simulated microgravity conditions was examined using a three-dimensional clinostat. The stems elongated with bending under such conditions. Stem elongation and leaf expansion were both promoted, whereas the formation of xylem in the secondary thickening growth was inhibited under the simulated microgravity condition. In secondary xylem, sedimentable amyloplasts were observed in the 1g control. The present results suggest that stem elongation and leaf expansion may be inhibited at 1g, while growth direction and secondary xylem formation depend on a gravity stimulus. A space experiment is expected to advance research on thickening growth in trees. Grant Numbers: 07456073, 1D 215.

Gravitation↗
PubMed1997

Effect of simulated microgravity and shear stress on microcin B17 production by Escherichia coli and on its excretion into the medium.

Production of the antibacterial polypeptide microcin B17 (MccB17) by Escherichia coli ZK650 was inhibited by simulated microgravity. The site of MccB17 accumulation was found to be different, depending on whether the organism was grown in shaking flasks or in rotating bioreactors designed to establish a simulated microgravity environment. In flasks, the accumulation was cellular, but in the reactors, virtually all the microcin was found in the medium. The change from a cellular site to an extracellular one was apparently not a function of gravity, since extracellular production occurred in these bioreactors, irrespective of whether they were operated in the simulated microgravity or normal gravity mode. More probably, excretion is due to the much lower degree of shear stress in the bioreactors. Addition of even a single glass bead to the 50-ml medium volume in the bioreactor created enough shear to change the site of MccB17 accumulation from the medium to the cells.

Anti-Bacterial Agents↗
PubMed2005

Cardiorespiratory responses to physical work during and following 17 days of bed rest and spaceflight.

To determine the influence of a 17-day exposure to real and simulated spaceflight (SF) on cardiorespiratory function during exercise, four male crewmembers of the STS-78 space shuttle flight and eight male volunteers were studied before, during, and after the 17-day mission and 17 days of -6 degrees head-down-tilt bed rest (BR), respectively. Measurements of oxygen uptake, pulmonary ventilation, and heart rate were made during submaximal cycling 60, 30, and 15 days before the SF liftoff and 12 and 7 days before BR; on SF days 2, 8, and 13 and on BR days 2, 8, and 13; and on days 1, 4, 5, and 8 after return to Earth and on days 3 and 7 after BR. During 15 days before liftoff, day 4 after return, and day 8 after return and all BR testing, each subject completed a continuous exercise test to volitional exhaustion on a semirecumbent (SF) or supine (BR) cycle ergometer to determine the submaximal and maximal cardiorespiratory responses to exercise. The remaining days of the SF testing were limited to a workload corresponding to 85% of the peak pre-SF peak oxygen uptake (Vo2 peak) workload. Exposure to and recovery from SF and BR induced similar responses to submaximal exercise at 150 W. Vo2 peak decreased by 10.4% from pre-SF (15 days before liftoff) to day 4 after return and 6.6% from pre-BR to day 3 after return, which was partially (SF: -5.2%) or fully (BR) restored within 1 wk of recovery. Workload corresponding to 85% of the peak pre-SF Vo2 peak showed a rapid and continued decline throughout the flight (SF day 2, -6.2%; SF day 8, -9.0%), reaching a nadir of -11.3% during testing on SF day 13. During BR, Vo2 peak also showed a decline from pre-BR (BR day 2, -7.3%; BR day 8, -7.1%; BR day 13, -9.0%). These results suggest that the onset of and recovery from real and simulated microgravity-induced cardiorespiratory deconditioning is relatively rapid, and head-down-tilt BR appears to be an appropriate model of this effect, both during and after SF.

Adult↗
PubMed2001

Effects of chronic exposure to simulated microgravity on skeletal muscle cell proliferation and differentiation.

Cell culture models that mimic long-term exposure to microgravity provide important insights into the cellular biological adaptations of human skeletal muscle to long-term residence in space. We developed insert scaffolding for the NASA-designed rotating cell culture system (RCCS) in order to study the effects of time-averaged microgravity on the proliferation and differentiation of anchorage-dependent skeletal muscle myocytes. We hypothesized that prolonged microgravity exposure would result in the retardation of myocyte differentiation. Microgravity exposure in the RCCS resulted in increased cellular proliferation. Despite shifting to media conditions promoting cellular differentiation, 5 d later, there was an increase in cell number of approximately 62%, increases in total cellular protein (52%), and cellular proliferating cell nuclear antigen (PCNA) content (2.7 times control), and only a modest (insignificant) decrease (10%) in sarcomeric myosin protein expression. We grew cells in an inverted orientation on membrane inserts. Changes in cell number and PCNA content were the converse to those observed for cells in the RCCS. We also grew cells on inserts at unit gravity with constant mixing. Mixing accounted for part, but not all, of the effects of microgravity exposure on skeletal muscle cell cultures (53% of the RCCS effect on PCNA at 4-6 d). In summary, the mechanical effects of simulated microgravity exposure in the RCCS resulted in the maintenance of cellular proliferation, manifested as increases in cell number and expression of PCNA relative to control conditions, with only a modest reciprocal inhibition of cellular differentiation. Therefore, this model provides conditions wherein cellular differentiation and proliferation appear to be uncoupled.

Animals↗
PubMed2006

Melanoma growth and tumorigenicity in models of microgravity.

INTRODUCTION: Spaceflight involves numerous biological stressors that could affect long-term cancer incidence and tumor behavior. Ground-based models of microgravity can be used to investigate in vitro and in vivo tumor growth as a preparation for later work in space. The incidence of tumor growth and carcinogenesis in microgravity is as yet unknown. Hence, we investigated the effects of modeled microgravity on tumor growth and tumorigenicity using ground-based in vitro and in vivo models. METHODS: Murine B16-F10 melanoma cells were cultured in a tissue culture flask (FL) and in a rotating-wall vessel bioreactor (BIO) designed by NASA to simulate some aspects of microgravity. We then measured cell growth, melanin production, and apoptosis. After 48 h of cultures in FL and BIO, cells were inoculated subcutaneously in C57BL/6 mice, syngeneic hosts for B16-F10 tumor cells. Tumor sizes were then measured every other day. RESULTS: BIO cultures had 50% decreases in growth when compared with FL cultures while demonstrating an inversely proportional increase in doubling time. Melanin production (a marker of differentiation) increased at 24 and 48 h in BIO. Flow cytometry analysis demonstrated that there was an increase in the percentage of apoptotic cells in the BIO when compared with that in the FL. When BIO-cultured melanoma cells were inoculated subcutaneously in mice, there was a significant increase in tumorigenicity as compared with FL-cultured cells. CONCLUSION: Our results indicate that simulated microgravity may have altered the tumor cell characteristics and enhanced the invasive property. It is possible that the microgravity analogue culture environment may have selected highly tumorigenic cells for survival despite the decreased overall growth in the microgravity analogue.

Animals↗
PubMed1989

Investigations on gel forming media for use in low gravity bioseparations research.

Microgravity research includes investigations designed to gain insight on methods of separating living cells. During a typical separation certain real-time measurements can be made by optical methods, but some materials must also be subjected to subsequent analyses, sometimes including cultivation of the separated cells. In the absence of on-orbit analytical or fraction collecting procedures, some means is required to "capture" cells after separation. The use of solutions that form gels was therefore investigated as a means of maintaining cells and/or macromolecules in the separated state after two types of simple ground-based experiments. Microgravity electrophoresis experiments were simulated by separating model cell types (rat, chicken, human and rabbit erythrocytes) in a vertical density gradient containing low-conductivity buffer, 1.7%-6.5% Ficoll, 6.8-5.0% sucrose, and 1% SeaPrep low-melting temperature agarose and demonstrating that, upon cooling, a gel formed in the column, and cells could be captured in the positions to which they had migrated. Two-phase extraction experiments were simulated by choosing two-polymer solutions in which phase separation occurs in normal saline at temperatures compatible with cell viability and in which one or both phases form a gel upon cooling. Suitable polymers included commercial agaroses (1-2%), maltodextrin (5-7%) and gelatin (5-20%).

Animals↗
PubMed2006

Renal stone risk in a simulated microgravity environment: impact of treadmill exercise with lower body negative pressure.

PURPOSE: Prolonged exposure to microgravity during spaceflight causes metabolic changes that increase the risk of renal stone formation. Studies during the Gemini, Apollo, Skylab and Shuttle missions demonstrated alterations in renal function, fluid homeostasis and bone resorption that result in increased urinary supersaturation of calcium oxalate, brushite, sodium urate and uric acid. Developing countermeasures to increased urinary supersaturation is an important priority as the duration of space missions increases. MATERIALS AND METHODS: A total of 11 sets of identical twins remained on 6-degree head down, tilt bed rest for 30 days to simulate prolonged microgravity. One twin per pair was randomly selected to exercise while supine in a lower body negative pressure chamber 6 days weekly for 40 minutes, followed by 5 minutes of resting lower body negative pressure at 50 mm Hg. The other twin served as a nonexercise control. Pressure in the exercise lower body negative pressure chamber (52 to 63 mm Hg) was adjusted to produce footward forces equivalent to those for upright running on Earth at 1.0 to 1.2 x body weight. Pre-bed rest urinary stone risk profiles were done elsewhere after 5 days of a standardized diet, consisting of 170 mEq sodium, 1,000 mg calcium, 0.8 gm/kg animal protein and 2,500 kcal, and then throughout the bed rest and recovery phases of the protocol. RESULTS: A significant increase in urinary calcium after just 1 week of bed rest was noted in the nonexercise control group (p = 0.001). However, no such increase was noted in the exercise group. Brushite supersaturation increased significantly from bed rest in each group, although the increase was significantly higher in the nonexercise control group than in the exercise group (p = 0.006). Calcium oxalate supersaturation increased during bed rest in the exercise group (p = 0.004). It trended toward a higher level in the nonexercise control group, although this did not achieve significance (p = 0.055) Mean urine volume +/- SD was significantly higher in the nonexercise control group than in the exercise group at bed rest week 2 and at week 3 (2.01 +/- 0.21 vs 1.63 0.18 l and 2.03 +/- 0.22 vs 1.81 +/- 0.20, respectively). Urinary pH was significantly higher in the nonexercise control group than in the exercise group at week 1 and week 3 (6.62 +/- 0.7 vs 6.49 +/- 0.5 and 6.58 +/- 0.6 vs 6.49 +/- 0.8, respectively, p = 0.01). CONCLUSIONS: Bed rest significantly alters the urinary environment to favor calculous formation. Lower body negative pressure chamber treadmill exercise offers some protection against increases in stone risk during simulated microgravity, particularly with regard to the risks of hypercalciuria and brushite stone formation. The use of lower body negative pressure to augment aerobic exercise in space may decrease the risk of stone formation in astronauts. Adjunct measures, including aggressive hydration and alkalinization therapy, should be considered.

Adult↗
PubMed2006

Alterations in the virulence potential of enteric pathogens and bacterial-host cell interactions under simulated microgravity conditions.

Host immune mechanisms were proposed to decline under microgravity conditions during spaceflights, which might result in severe infections in astronauts. Therefore, it was important to investigate the effects of microgravity on infecting organisms and their interaction with host cells. Data showed that simulated microgravity (SMG) conditions markedly increased production of the enterotoxigenic Escherichia coli (ETEC) heat-labile enterotoxin, which induced fluid secretory responses in a mouse model. SMG also enhanced production of tumor necrosis factor-alpha in murine macrophages infected with enteropathogenic E. coli (EPEC). In a similar fashion, simulated microgravity conditions augmented the invasive potential of Salmonella enterica serovar typhimurium and enhanced production of tumor necrosis-factor alpha in S. typhimurium-infected epithelial cells. Furthermore, coculturing of macrophages and S. typhimurium in a simulated microgravity environment resulted in activation of stress-associated mitogen-activated protein kinase kinase 4. Using the antiorthostatic tail suspension mouse model, which simulates some aspects of microgravity, oral inoculation of S. typhimurium markedly reduced the 50% lethal dose compared to mice infected under normal gravitational conditions. Microarray analysis revealed simulated microgravity-induced alterations in the expression of 22 genes in S. typhimurium, and protein expression profiles were altered in both EPEC and S. typhimurium, based on two-dimensional gel electrophoresis. These studies indicated alterations in the virulence potential of bacteria and in host responses to these pathogens under simulated microgravity conditions, which may represent an important environmental signal. Such studies are essential for better understanding bacterial-host cell interactions, particularly in the context of spaceflights and space habitations of long duration.

Animals↗
PubMed2000

Alterations in skeletal perfusion with simulated microgravity: a possible mechanism for bone remodeling.

Bone loss occurs as a consequence of exposure to microgravity. Using the hindlimb-unloaded rat to model spaceflight, this study had as its purpose to determine whether skeletal unloading and cephalic fluid shifts alter bone blood flow. We hypothesized that perfusion would be diminished in the hindlimb bones and increased in skeletal structures of the forelimbs and head. Using radiolabeled microspheres, we measured skeletal perfusion during control standing and after 10 min, 7 days, and 28 days of hindlimb unloading (HU). Femoral and tibial perfusion were reduced with 10 min of HU, and blood flow to the femoral shaft and marrow were further diminished with 28 days of HU. Correspondingly, the mass of femora (-11%, P < 0. 05) and tibiae (-6%, P < 0.1) was lowered with 28 days of HU. In contrast, blood flow to the skull, mandible, clavicle, and humerus was increased with 10 min HU but returned to control levels with 7 days HU. Mandibular (+10%, P < 0.05), clavicular (+18%, P < 0.05), and humeral (+8%, P < 0.1) mass was increased with chronic HU. The data demonstrate that simulated microgravity alters bone perfusion and that such alterations correspond to unloading-induced changes in bone mass. These results support the hypothesis that alterations in bone blood flow provide a stimulus for bone remodeling during periods of microgravity.

Animals↗
PubMed1998

Male reproductive system in conditions of bed-rest in a head-down tilt.

Study of reproductive function in simulating experiments is important as for expansion of our theoretical knowledge in the field of gravitational physiology and space biology and for the decision of applied problems in space and clinical medicine. Long-term bed rest in a head-down tilt--6 degrees (BRHDT)--antiorthostatic hypokinesia is a wide spread method for ground-based simulation of space flight's conditions (mainly of hemodynamical effects of microgravity and restriction of locomotor activity). The aim of the present research was to study a reproductive function in males during 60-120 day BRHDT.

Adult↗
PubMed2000

[Ground-based studies on thermoregulation at simulated microgravity by head-down tilt bed rest].

Comparisons of headward fluid shifts, plasma volume losses, altered vasodilator and vasoconstrictor responses, reduced exercise capacities, etc. between microgravity and head-down tilt (HDT) bedrest suggested that HDT model was suitable for simulating thermoregulation under microgravity. Both microgravity and simulated microgravity by HDT exposures degraded human thermoregulation ability in some aspects. The features of the responses to heat stress on men after HDT exposures were higher increase rate in rectal temperature, attenuated increase rates of skin temperature and body heat conductance, less heat dissipation from core to skin and higher sensitivity of sweating etc.

Bed Rest↗
PubMed2003

Growth and development, and auxin polar transport of transgenic Arabidopsis under simulated microgravity conditions on a three-dimensional clinostat.

Growth and development, and auxin polar transport in Arabidopsis thaliana transformed with iaaH gene were studied under simulated microgravity conditions on a three-dimensional (3-D) clinostat. Simulated microgravity conditions on a 3-D clinostat did not affect the number of rosette leaves but promoted the growth and development (fresh weight of plant and the elongation of flower stalk) of transformants. Final growth of transformants under simulated microgravity conditions on a 3-D clinostat was almost equivalent to that grown on 1 g conditions in the presence of 1 micromoles IAM (indole-3-acetamide). The activities of auxin polar transport in the segments of flower stalk (inflorescence axis) of transformants grown on 1 g conditions were significantly promoted by the addition of IAM. Interestingly, simulated microgravity conditions on a 3-D clinostat also promoted the activities of auxin polar transport of transformants grown on the medium with or without IAM. Based on the results in this study, transgenic plants may not have an efficient homeostatic mechanism for the control of growth and development, and auxin polar transport activity in microgravity conditions in space.

Arabidopsis↗
PubMed2002

[Effects of simulated microgravity on cardiovascular function and counter effect of lower body negative pressure].

Studies on effect of simulated microgravity on cardiovascular function and counter effect of lower body negative pressure (LBNP) in recent years were summarized. The mechanism of simulated microgravity induced orthostatic intolerance may involve the reduction of cardiovascular function and cerebral blood flow, and endocrine changes. The significance of mathematical model in the study of mechanism of microgravity induced orthostatic intolerance was also discussed. The counter effect of LBNP was emphasized.

Bed Rest↗
PubMed1991

From gravity and the organism to gravity and the cell.

This workshop on Gravity and the Cell was modeled on a 1968 conference on Gravity and the Organism. Each conference tried to identify the most salient scientific questions about how gravity is important to living systems. In the roughly two decades between the conferences there have been impressive advances in experimental methods, but the major scientific questions that have driven their applications to problems of gravitational biology, i.e., our broad research goals, remain much the same. In the case of plant research, improvements and extensions of biochemical techniques for investigating the ways organisms use environmental (g-force) information in salubrious ways has kept pace with progress in plant biochemistry. We now know much more about the roles of organic and inorganic substances that plants employ for information transfer and growth regulation and about the avenues and mechanisms for transport of those key substances within organisms. We have seen the acceptance of a "local control" concept that regulation of g-responses depends critically on plasmodesmata and gap junctions which allow plants and animals to throttle the transport of growth regulators across tissue boundaries often, especially in the case of plants, far removed from the morphological regions of concentration of statocytes that were once thought to be the exclusive bioaccelerometers used by plants. NASA's sponsorship of ground-based research in gravitational biology has served as important underpinning for orbital flight programs in space biology. The currently most noteworthy research area of ignorance is the mechanism by which the physical event of g-force susception becomes the biological process of g-force perception. Only rarely has it been possible to perform a definitive test of a theory of mechanism of gravity perception. Therefore, experimental research efforts in gravitational physiology still are essentially dependent on exploratory studies for which stimulus/response experiments require experimental manipulation of test subjects' g-force environment. Many research efforts have focused narrowly on contrasting the responses of test subjects to only two gravitational environments, 1 g versus real or simulated zero g. Much less effort has been devoted to studies at other g levels. For experiments in gravitational physiology three rotating machines have made, and no doubt will continue to make, important contributions: the centrifuge, the clinostat, and, most of all, the orbiting space vehicle. Some research trends, viewpoints, and shifts of emphasis are discussed.

Animals↗
PubMed1998

Influence of bisphosphonates on calcium metabolism and bone tissue during simulation of the physiological effects of microgravity.

At present a significant experience has been gathered in experimental and clinical use of synthetic derivatives of bisphosphonic acid. Purpose of our study was to investigate the effects of bisphosphonates on calcium metabolism and bone tissue in humans and animals under the conditions simulating the physiological effects of microgravity. In a series of experiments with animals the effectiveness of various preparations and treatment plans was compared Action of 1-hydroxyethyliden-1, 1-bisphosphonic acid (EHBP, xydiphon) on calcium metabolism and bone tissue in human was the subject of experiments with long-term head-down tilt (HDT).

Animals↗
PubMed1967

The influence of simulated low-gravity environments on growth, development and metabolism of plants.

Low-gravity environments may be simulated through appropriate horizontal clinostat rotation. This simulation is accomplished through a biological nullification of the directional component of gravitational force. Measuring biologically effective gravity force by organ response, it is readily demonstrated that biologically active gravitational force may be treated as a two-dimensional vector. Though the magnitude dimension of this vector remains virtually constant anywhere on earth, the biologically effective direction dimension may be quantitatively altered by clinostat rotation, provided appropriate angular velocities and angles of inclination of clinostat axes are employed. Using oat seedlings, a rotation rate of 2 rpm, and a horizontal axis clinostat, a 'zero g' environment may be simulated. This simulated 'zero g' condition is attested by the inability of plants to perceive unidirectional gravitational force of sufficient magnitude to elicit directional growth. Under such conditions, plants will grow in the direction imparted by the initial orientation of the plants in the system. Geotropic curvature responses to subsequent geostimulation are, however, greater in seedlings grown under these conditions, nullifying the direction dimension of gravitational force, than in seedlings grown with rotation but with normal unidirectional gravity loads. Root growth under simulated 'zero' gravity conditions is likewise enhanced as compared to plants grown with rotation but normal unidirectional gravity. These differences in magnitude of growth and response to subsequent geostimulation are inexplicable on bases of modified auxin economy or production. Respiration rates are, however, materially enhanced by the simulated 'zero g' environments. This enhancement of respiration, as well as growth, quantitatively diminishes as the unidirectional gravity load is increased. These results imply that the primary effect of low-gravity environments is likely that of modifying the magnitude of respiratory metabolism. Such a modification is partly or wholly explicable on a basis of a modified distribution pattern of metabolically active particulate cell inclusions.

Avena↗
PubMedDate not supplied

[Morphology of vessels and vascular plexus in the rat's brain following 93-day simulation of the effects of microgravity].

Results of the histological analysis of the brain of rats subjected to 93-d tail-suspension reveal morphological changes occurred to the arteries, veins and capillaries, ependymal cells of the ventricles and epithelium of the vascular plexus, and nervous and glial cells. On the one hand, these suggest venostatis and brain edema, impaired liquor production and liquor dynamics and increase in intracranial pressure and, on the other hand, adaptive processes in the arterial walls preventing the excess blood flow to the brain.

Adrenal Glands↗