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PubMedDate not supplied

[Correlation of fluctuations in the activity of the rat monooxygenase system with dynamics of tidal gravitational changes].

Semi-annual changes in monthly average levels of functioning of the rat liver monooxygenase system in norm (the amidopyrine test) were found. It was shown that there are inverse linear correlations between the level of demethylation and acetylation of amidopyrine and the semi-annual periodicity of average monthly data on the acceleration of tide changes in gravity.

Acetylation↗
PubMedDate not supplied

[Effect of systematic gravitational forces on the external respiration function in conditions of prolonged immersion].

Test subjects were exposed to 13-day water immersion per se or combined with centrifugation. The immersion did not influence the state of ventilation and gas exchange at rest, diminished significantly the functional capabilities of external respiration. An exposure of the test subjects to acceleration during the second half of water immersion resulted in the normalization of the functional reserves of external respiration. This may be a consequence of an increase in the total physical tone of the body.

Adult↗
PubMed2001

Altered gravitational forces affect the development of the static vestibuloocular reflex in fish (Oreochromis mossambicus).

Young fish (Oreochromis mossambicus) were exposed to microgravity (micro g) for 9 to 10 days during space missions STS-55 and STS-84, or to hypergravity (hg) for 9 days. Young animals (stages 11-12), which had not yet developed the roll-induced static vestibuloocular reflex (rVOR) at micro g- and hg-onset, and older ones (stages 14-16), which had already developed the rVOR, were used. For several weeks afterwards, the rVOR was recorded after termination of mug and hg. Here are the main results: (1) In the stage 11-12 fish, the rVOR gain (response angle/roll angle) measured for roll angles 15 degrees, 30 degrees, and 45 degrees was not affected by microgravity if animals were rolled from the horizontal to the inclined posture, but was increased significantly if animals were rolled in the opposite manner. The rVOR amplitude (maximal eye movement during a complete 360 degrees roll) of micro g animals increased significantly by 25% compared to 1g controls during the first postflight week, but decreased to the control level during the second postflight week. Microgravity had no effect in stage 14-16 fish on either rVOR gain or amplitude. (2) After 3g exposure, both rVOR gain and amplitude were significantly reduced for both stage 11-12 and stage 15 fish. One g readaptation was completed during the second post-3g week. Hypergravity at 2 or 2.5 g had no effect. (3) Hypergravity at all three levels tested (2g, 2.5g, and 3g) accelerated the morphological development as assessed by external morphological markers. Exposure to micro g- or 3g-periods during an early developmental period modifies the physiological properties of the neuronal network underlying the static rVOR; in susceptible developmental stages, these modifications include sensitization by microgravity and desensitization by hypergravity.

Animals↗
PubMed2006

Changes in gravitational force cause changes in gene expression in the lens of developing zebrafish.

Gravity has been a constant physical factor during the evolution and development of life on Earth. We have been studying effects of simulated microgravity on gene expression in transgenic zebrafish embryos expressing gfp under the influence of gene-specific promoters. In this study, we assessed the effect of microgravity on the expression of the heat shock protein 70 (hsp70) gene in lens during development using transgenic zebrafish embryos expressing gfp under the control of hsp70 promoter/enhancer. Hsp70:gfp expression was up-regulated (45%) compared with controls during the developmental period that included the lens differentiation stage. This increase was lens specific, because the entire embryo showed only a 4% increase in gfp expression. Northern blot and in situ hybridization analysis indicated that the hsp70:gfp expression recapitulated endogenous hsp70 mRNA expression. Hypergravity exposure also increased hsp70 expression during the same period. In situ hybridization analysis for two lens-specific crystallin genes revealed that neither micro- nor hypergravity affected the expression level of betaB1-crystallin, a non-hsp gene used as a marker for lens differentiation. However, hypergravity changed the expression level of alphaA-crystallin, a member of the small hsp gene family. Terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) assay analysis showed that altered-gravity (Deltag) decreased apoptosis in lens during the same period and the decrease correlated with the up-regulation of hsp70 expression, suggesting that elimination of nuclei from differentiating lens fiber cells was suppressed probably through hsp70 up-regulation. These results support the idea that Deltag influences hsp70 expression and differentiation in lens-specific and developmental period specific manners and that hsp family genes play a specific role in the response to Deltag.

Animals↗
PubMed1987

Mass transport in dissolution kinetics. II: Convective diffusion to assess role of viscosity under conditions of gravitational flow.

Dissolution kinetics was studied in a laminar flow cell, through which aqueous solutions of increasing viscosity flowed under the force of gravity, in order to help elucidate the mechanism of drug dissolution. The viscosity was varied by addition of either hydroxypropyl cellulose, sucrose, or glycerin. The dissolution data were evaluated quantitatively in terms of a convective diffusion model for dissolution. It was demonstrated that the decrease in dissolution rate of a test compound due to viscosity in the polymer solution occurs primarily because of a decrease in the rate of shear over the dissolving surface. In solutions of sucrose or glycerin, the decrease in dissolution rate due to viscosity results because of a decrease in the diffusivity of the solute in addition to the decreased rate of shear. Also, the model accounts for the increase in solubility in the glycerin solution. Thus, the influence of viscosity on dissolution depends on whether the viscosity-inducing agent primarily affects only the flow properties of the liquid, or whether it affects diffusivity (i.e., a "micro" viscosity effect, in addition to the flow properties).

Cellulose↗
PubMed1997

Effects of intermittent or continuous gravitational stresses on cell-matrix adhesion: quantitative analysis of focal contacts in osteoblastic ROS 17/2.8 cells.

The relationship between cell morphology and cell metabolism and the role of mechanical load in bone remodeling is well known. Mechanical stimulation induces changes in the shape of osteoblasts, probably mediated by reorganization of focal contacts. We studied the influence of gravity (Gz) variations occurring during parabolic flight on osteoblast focal adhesion of ROS 17/2.8 osteosarcoma cells subjected to 15 or 30 parabolic flights. Significant flight-induced shape changes consisted of decreased cell area associated with focal contact plaque reorganization. Identical durations of continuous mechanical stress induced by centrifugation (2 Gz) or clinorotation (Gz randomization) had no major effect on cell focal adhesion. ROS 17/2.8 G2/M synchronization by treatment with nocodazole inhibited the flight-induced decrease in adhesion parameters. We concluded that ROS 17/2.8 cells are sensitive to Gz switches and that their adaptation is at least dependent on microtubule function.

Animals↗
PubMed1999

Gravitational Drainage of a Tangentially-Immobile Thick Film.

We use lubrication theory to derive an evolution equation for the free surface of a draining thick free film with a zero tangential velocity component along the free surface. The films are "thick" because effects that are important in very thin films, such as intermolecular forces, do not play a role in the situation of interest. The evolution equation results from the balance of surface tension, gravity, and dynamic viscosity. Subregions of the film appear and they involve balancing these effects pairwise. Computations are performed on the full evolution equation and for various boundary conditions corresponding to different parts of the film. Matched asymptotics are developed that predict the behavior as the film enters the bath and these agree very well with the computed results. Comparison with experiment is favorable for the rate of decrease of the film thickness. Copyright 1999 Academic Press.

Journal Article↗
PubMed2002

Batch gravitational sedimentation of slurries.

We investigated the batch settling behavior of the kaolin slurry and the UK ball clay slurry at various initial solids fractions (phi(0)s) using a computerized axial tomography scanner (CATSCAN). The spatio-temporal evolutions of solids fractions in the consolidating sediments were continuously monitored. Since the interface between the sediment and the supernatant of the investigated slurries was blurred, an averaging procedure was employed to estimate their null-stress solids fractions (phi(g)s). Besides the rather slow settling for the high-phi(0) slurries, the basic settling characteristics resemble each other regardless of whether phi(0)>phi(g) or vice versa. The above-mentioned experimental data reveal that the investigated slurries are neither purely elastic nor purely plastic in rheological behavior. On contrary to most model works a blurred supernatant-sediment interface makes difficulty in the gel point determination. During initial settling the high-phi(0) slurries clearly exhibit a finite yield stress to resist deformation. That is, the slurries are plastic fluids. However, the network structure in the slurries deteriorates gradually in the subsequent settling stage while the final, equilibrated sediment reveals a continuous distribution in solids fraction. Restated, the final sediment possesses as a purely elastic characteristic. The model parameters of theory by Buscall and White were regressed by the dynamic consolidating sediment data, while those by Tiller and Leu were obtained using the final equilibrated sediment data. Calculations from both models reveal that ball clay slurry is more compressible than is the kaolin slurry. The high-phi(S0) slurry would yield the less compressible sediment.

Journal Article↗
PubMed2006

Auxin transport and gravitational research: perspectives.

Gravity is a fundamental factor which affects all living organisms. Plant development is well adapted to gravity by directing roots downward and shoots upwards. For more than a century, plant biologists have been fascinated to describe the molecular mechanisms underlying the gravitropic response of plants. Important progress towards signal perception, transduction, and response has been made, but new tools are beginning to uncover the regulatory networks for gravitropic control. We summarise recent progress in study of gravitropism and discuss strategies to identify the molecular basis of the gravity response in Arabidopsis thaliana. This will put us on a road towards the molecular systems biology of the Arabidopsis gravitropic response.

Arabidopsis↗
PubMed1982

Human adaptation to simulated gravitational fields.

We present the resuIts of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the role of functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g.

Acceleration↗
PubMed1990

Biological and cognitive determination of the gravitational reference frame.

It is argued that space sickness is not so much a physiological problem, but a psychological one, having its roots in the perception of the environment, and its associated cognitive processing. This cognitive processing is argued to be that of field dependence and field independence, for which exist psychobiological and cognitive assessment tests. Since there is an obvious economic advantage in the use of cognite testing, it is recommended that this could be used as an initial screening when selecting for astronauts.

Aerospace Medicine↗
PubMed1994

Individual differences of cerebrovascular responses to gravitational stress--prediction of orthostatic intolerance.

This experiment was designed to investigate the individual differences in the cerebrovascular responses to orthostatic stress. Seven male volunteers were exposed to head-up tilt (HUT) at 60 degrees for 15 min and to lower body negative pressure (LBNP) at 30 mmHg for 25 min. We measured the flow velocity of the middle cerebral artery and the quantity of the oxygenated and deoxygenated hemoglobin (oxy-Hb and deoxy-Hb) in the brain. Based upon oxy-Hb change during exposure to HUT, we classified the subjects into two groups: 1) the "good responder" group in which the oxy-Hb gradually increased from the 5th to 10th minute of HUT; 2) the "bad responder" group in which the oxy-Hb stabilized at lower levels after the initial decrease. The oxy-Hb changes between the two groups were significantly different during exposure to LBNP. During exposure to HUT and LBNP, no significant difference was observed in blood pressure and heart rate between the two groups. Our results suggest that there might be an individual difference in the cerebrovascular responses to orthostatic stress.

Adult↗