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At least 1,441 records · Page 80Linked to original sources
PubMed2001

Bioglass (R) stimulation of embryonic long-bones in altered loading environments.

The 45S5 composition glass (Bioglass (R), USBiomaterials, USA) contains 45 wt% SiO2, 24.5 wt% CaO, 24.5 wt% Na2O and 6 wt% P2O5. It is a low SiO2 (45 wt%) and a high Na2O content glass that results in rapid ion exchange when exposed to physiological solutions. The change in local solution chemistry results in rapid nucleation (1-3 hours exposure) and subsequent crystallisation of hydroxyl-carbonate-apatite (HCA) identical to naturally occurring bone mineral within a hydrated SiO2-rich layer developed on the glass surface. During HCA layer formation, proteins and other growth factors are absorbed into the layer. The synthetic bone mineral layer bonds to collagen, produced by the host tissue, which leads to a strong interfacial bond that is stronger than the host tissue (hard or soft) (Hench and West. 1996). In this study we show that the chemical effects responsible for enhanced bone cell proliferation and differentiation found in-vitro and in-vivo with Bioglass (R) may be sufficient to prevent the demineralisation of bone tissue that occurs as a result of ageing or exposure to a low loading environment i.e. implant/tissue stress-shielding, space-flight.

Animals↗
PubMed2001

Effect of long-term bedrest on lower leg muscle activation patterns during quiet standing.

It has been well known that balance instabilities after long-term exposure to microgravity (e.g., Anderson et al. 1986) or bedrest (BR) can be related to alterations and/or adaptations to postural control strategies. Little is known, however, how the reduced muscular activity affects the activation pattern of the lower limb muscles during quiet standing (QS). The purpose of this study was to investigate whether or not any changes in the lower limb muscle activation patterns during QS would occur after BR.

Adult↗
PubMed2001

Modern view on the short-arm centrifuge as a potential generator of artificial gravity in piloted missions.

The problem of artificial gravity (AG) in long-term missions is one of the hottest, as the existing countermeasures do not fully cope with the negative consequences of weightlessness. From two variants of AG creation--rotation of space systems around of their mass center or short radius centrifuge (SAC)--the preference is given to SAC, as technically easier variant for realization. However, the rotation of a person on SAC can cause not only positive, but also negative effects. The purpose of the present study was to perform the analysis of data of researches on a problem of AG generated by a of SAC, executed in Russia during last 20 years, and to state modern views on application of SAC as a mean of AG creation in long piloted missions.

Adaptation, Physiological↗
PubMed1976

Antiorthostatic test as a model to study antigravity mechanisms of the cardiovascular system.

The paper presents rheographic investigations of regional haemodynamics (brain, lungs, liver and limbs) during antiorthostatic exposures of varying intensity (-15, -30, -45 degrees, times of exposure 20, 40 and 60 min). Our findings show that the pattern and time of the function of compensatory mechanisms preventing excessive vascular compliance [correction of complicance] under the influence of the hydrostatic blood column depend on the value and length of antiorthostasis, because prolonged venous congestion results not only in congestive circulatory hypoxia but also in arterial hypoxia due to compensatory limitation of arterial inflow.

Adult↗
PubMed1976

Metabolic processes in hypokinetic and rehabilitated men.

The present paper summarizes the experimental data on influence of antiorthostatic hypokinesia (49 days) and rationalized nutrition during the rehabilitation period (30 days) on metabolic processes. On the basis of these data a well balanced diet is recommended for the rehabilitation period which follows a long-term bed rest.

Adaptation, Physiological↗
PubMed1976

Effect of antiorthostatic bed rest on the human body.

Head-down (-4 degrees) bedrest brings about a more rapid development of changes in haemodynamics, fluid displacement and nervous tone than traditional recumbent bed rest. Changes occurring during head-down hypokinesia have much in common with the changes typical of real weightlessness. They are characterized by phasic changes in the vascular tone. Under these conditions changes in the tone and blood-filling of the brain are important for the functional state of the vestibular apparatus.

Adaptation, Physiological↗
PubMed2002

Role of afferent input in muscle atrophy.

It is well known that soleus muscle of rat atrophies following spaceflight or hindlimb suspension (Ohira et al., 1992). It is, further, reported that the electromyogram (EMG) of soleus muscle disappears immediately in response to unloading by exposure to actual micro-g environment (Kawano et al., 2002; Leterme and Falempin, 1998) and by hindlimb suspension of rats (Alford et al., 1987; Ohira et al., 2000). However, the EMG level is increased gradually to the control level following 7-10 days of continuous hindlimb suspension (Alford et al., 1987; Ohira, 2000), while muscle atrophy is progressing (Winiarski et al., 1987). We previously reported that reduction of the EMG level of rat soleus in response to actual micro-g environment, created by a parabolic flight of a jet airplane, was closely associated with a decrease of the afferent input recorded at the L5 segmental level of spinal cord (Kawano et al., 2002). However, it is still unclear how the EMG level of soleus muscle adapts to unloading condition. The current study was performed to investigate the responses of soleus EMG and both afferent and efferent neurogram at the L5 segmental level of spinal cord to acute (20 seconds) and chronic (14 days) unloading.

Animals↗
PubMed2002

[Research plan to study allelopathy under microgravity].

Living organisms interact each others and form ecological system on the earth. Such interactions between organisms and species have been long known, and studied at a global scale. Allelopathy is a phenomenon observed in many plants that emit specific chemicals acting on other organisms, including animals and microorganisms, in either inhibitory or excitatory ways. We propose to study whether phenomena of allelopathy are modified under altered gravity or not. If biosynthesis, emission and sensing mechanism of allelopathic substances would be affected by gravity, many organisms and ecological system might show different behaviors based on the inter-organisms and species interactions under microgravity. In the macroscopic scale, transport of the substances between organisms is largely affected by convection induced by gravity. Furthermore, the fate of allelopathic substances in confined environment differs from that seen on the earth, because of lacking sink compartment for removal and producing exotic bio-active substances by man-made system. We design basic ground experiment to evaluate gravitational effects on allelopathy applying pseudo-microgravity. Our study contributes to the synthesis of ecological system and its control on spacecrafts and extraterrestrial bodies. It also makes possible to sustain qualitative human life even on the ground under confined artificial environment that dominates in many scenes.

Agriculture↗
PubMed2002

[Effects of clinorotation on the structure of xylem in Arabidopsis roots].

Lignin, which is the most important component of vascular tissue, is essential material for the structural support of higher plants and considered to play a critical role in evolution of land plants. It has been postulated that development of secondary wall is mediated by gravity. However, effects of gravity on the development and the morphology of secondary cell wall have not been well investigated. In this study, effects of averaging of gravity vector using 2-D clinostat rotation on the structure of xylem was examined. The results indicated that the morphology of xylem is regulated by the orientation of gravity vector.

Arabidopsis↗
PubMed2002

[Change of the gene expression related to a cytoskeleton cultured under gravity-vector changing].

Many researches to elucidate the mechanism of gravity sense and its response in the living cells have been advanced. But it has not yet identified that key molecule or signal transduction pathway related to gravity sense and its response. Our goal is to clarify the mechanism of gravity sense, especially the point of gravity sense. First, we have investigated about differences of gene expression level (mRNA) of the endothelial cells cultivated under vector-averaged gravity condition (Clinorotation). The Differential Display pattern showed that expression level of several genes had changed between clinorotated condition and control. The homologues of these fragments were searched on the BLAST database. From BLAST database searching results, GEF and cell adhesion protein effected by clinorotaion. Moreover, morphological and immunological techniques data showed that the cytoskeletal formation of actin, tubulin, etc. or localization in cell of Rho protein were changed. These results suggested that signal transduction pathway through Rho played an important role in the gravity sense mechanism of endothelial cells. Furthermore, we are going to investigate relation between gene expression and morphological data.

Cells, Cultured↗
PubMed2000

Renal responsiveness to aldosterone during exposure to head-down tilt bedrest.

The kidneys represent a fundamental organ system responsible in part for the control of vascular volume. A 10% to 20% reduction in plasma volume is one of the fundamental adaptations during exposure to low gravity environments such as bedrest and space flight. Bedrest-induced hypovolemia has been associated with acute diuresis and natriuresis. Elevated baseline plasma renin activity and aldosterone levels have been observed in human subjects following exposure to head-down tilt and spaceflight without alterations in renal sodium excretion. Further, attempts to restore plasma volume with isotonic fluid drinking or infusion in human subjects exposed to head-down bedrest have failed. One explanation for these observations is that renal distal tubular cells may become less sensitive to aldosterone following exposure to head-down tilt, with a subsequent reduction in renal capacity for sodium retention. We hypothesized that elevated sodium and water excretion observed during prolonged exposure to bedrest and the subsequent inability to restore body fluids by drinking might be reflected, at least in part, by reduced renal tubular responsiveness to aldosterone. If renal tubular responsiveness to aldosterone were reduced with confinement to bedrest, then we would expect measures of renal sodium retention to be reduced when a bolus of aldosterone was administered in head-down tilt (HDT) bedrest compared to a control experimental condition. In order to test this hypothesis, we conducted an investigation in which we administered an acute bolus of aldosterone (stimulus) and measured responses in renal functions that included renal clearances of sodium and free water, sodium/potassium ratio in urine, urine sodium concentration, and total and fractional renal sodium excretion.

Aldosterone↗
PubMed2000

Arterial baroreflex control of sympathetic vasoconstrictor traffic and orthostatic intolerance after head-down bed rest.

The purpose of the present study is to examine the changes in the arterial baroreflex control of muscle sympathetic nerve activity (MSNA) after head-down bed rest (HDBR), in relation to orthostatic hypotension after HDBR. Therefore, we performed 60 degrees head-up tilt (HUT) tests before and after 14 days of HDBR, with monitoring MSNA, heart rate and blood pressure. We calculated the gain of the arterial baroreflex control of MSNA, and compared the gains between the subjects who did (defined as the fainters) and those who did not (defined as the nonfainters) become presyncopal in HUT tests after HDBR.

Adult↗
PubMed2000

Elaboration of on-board automated training system.

UNLABELLED: Long-term space flight requires regular controlling of crewmembers physical state and exercise training to prevent negative effect of microgravity. Considering a limited telecommunication we suppose on-board automated training system to become an effective alternative of on-earth mission teams. THE PURPOSE: to elaborate an expert system software permitting to automate the process of solution elaboration to estimate cosmonaut current psycho-physiological state and to form an individual program of physical training to prevent negative effects of long-term space flight. The first problem--to develop a formalized algorithm for expert evaluation of physical working capability basing the results of on-board compulsory running test MC 108-2.

Adult↗
PubMed2000

Altered gravity modulates prostaglandin H synthase in human K562 cells.

In this study, we extended our previous observations on the effects of altered gravity on the "lipoxygenase pathway", by ascertain the possible role of the force of gravity in modulating the activity and expression of PHS in human erythro-leukemia K562 cells.

Arachidonate 5-Lipoxygenase↗
PubMed2000

Disuse bone loss in hindquarter suspended rats: partial weightbearing, exercise and ibandronate treatment as countermeasures.

The purpose of this study was to evaluate potential countermeasures for bone loss during long-term space missions in the hindquarter suspended rat, including partial weight bearing (surrogate for artificial gravity) episodic full weight bearing (2 hour/day full weight bearing) and treatment with the third generation bisphosphonate ibandronate (Roche). Graded mechanical loading was studied by housing the animals on a novel servo controlled force plate system which permitted the titration of mechanical force at varying frequency and amplitude and different levels of weight bearing. The force plate, which forms the cage floor, is a glass platform supported by an 18" diameter speaker cone filled with expanding polyurethane foam. An infrared optical sensor attached to the speaker cone yields a voltage linearly related to vertical displacement of the glass platform. The dynamic force on the paw was computed as a product of the apparent mass of the animal on the platform at rest and the acceleration of the platform determined from the second derivative of the optical sensor output. The mass of the animal on the platform was varied by adjusting tension on the tether suspending the animal. Mechanical impact loading was titrated with the force plate resonating at different frequencies, including 3 Hz and 16 Hz.

Animals↗