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At least 505 records · Page 28Linked to original sources
PubMed2003

Hypotensive effect of push-pull gravitational stress occurs after autonomic blockade.

The "push-pull" effect denotes the reduced tolerance to +Gz (hypergravity) when +Gz stress is preceded by exposure to hypogravity, i.e., fractional, zero, or negative Gz. Previous studies have implicated autonomic reflexes as a mechanism contributing to the push-pull effect. The purpose of this study was to test the hypothesis that nonautonomic mechanisms can cause a push-pull effect, by using eye-level blood pressure as a measure of G tolerance. The approach was to impose control (30 s of 30 degrees head-up tilt) and push-pull (30 s of 30 degrees head-up tilt immediately preceded by 10 s of -15 degrees headdown tilt) gravitational stress after administration of hexamethonium (10 mg/kg) to inhibit autonomic ganglionic neurotransmission in four dogs. The animals were chronically instrumented with arterial and venous catheters, an ascending aortic blood flow transducer, ventricular pacing electrodes, and atrioventicular block. The animals were paced at 75 beats/min throughout the experiment. The animals were sedated with acepromazine and lightly restrained in lateral recumbency on a tilt table. After the onset of head-up tilt, the magnitude of the fall in eye-level blood pressure from baseline was -27.6 +/- 2.3 and -37.9 +/- 2.7 mmHg for the control and push-pull trials, respectively (P < 0.05). Cardiac output fell similarly in both conditions. Thus a push-pull effect attributable to a rise in total vascular conductance occurs when autonomic function is inhibited.

Animals↗
PubMed1996

Development of centrifugal phytotron to study the gravity effect on vegetable plant growth.

The present Spacetron is used to cultivate plants over a long term by controlling environment condition. The cultivation drum was rotated in perpendicular direction creating fluctuation in gravity. Centrifugal force plus 1 G ground gravity, are distributed unevenly over the cultivation drum. This fluctuation effect on plant growth was not clear. In the modified Spacetron the cultivation drum rotates horizontally whereas the plant stage rotated in the perpendicular direction. To find the basic information for design of centrifugal phytotron the two axes Spacetron Junior (clinostat) was developed to formulate the micro and hypergravity environment. It would be used to study the effect on a plant growth process of different gravity conditions. In order to produce the different values of gravity, the clinostat's axis was rotated with a stepping motor at different angular velocity. The axis rotated at 5.2 revolutions per minute (rpm) to create a centrifugal force equivalent to 0.01 G and the plant stage was rotated at 5.2 rpm. The chlorophyll value is higher in the plants under microgravity condition of 0.01 G whereas the fresh weight and dry weight are higher in the plants under control condition of 1 G earth gravity. The result of this study showed that the plant growth was affected by microgravity along with other known factors such as vibration and unknown factors.

Biomass↗
PubMed2003

[Gravity resistance, another graviresponse in plants--function of anti-gravitational polysaccharides].

The involvement of anti-gravitational polysaccharides in gravity resistance, one of two major gravity responses in plants, was discussed. In dicotyledons, xyloglucans are the only cell wall polysaccharides, whose level, molecular size, and metabolic turnover were modified under both hypergravity and microgravity conditions, suggesting that xyloglucans act as anti-gravitational polysaccharides. In monocotyledonous Poaceae, (1-->3),(1-->4)-beta glucans, instead of xyloglucans, were shown to play a role as anti-gravitational polysaccharides. These polysaccharides are also involved in plant responses to other environmental factors, such as light and temperature, and to some phytohormones, such as auxin and ethylene. Thus, the type of anti-gravitational polysaccharides is different between dicotyledons and Poaceae, but such polysaccharides are universally involved in plant responses to environmental and hormonal signals. In gravity resistance, the gravity signal may be received by the plasma membrane mechanoreceptors, transformed and transduced within each cell, and then may modify the processes of synthesis and secretion of the anti-gravitational polysaccharides and the cell wall enzymes responsible for their degradation, as well as the apoplastic pH, leading to the cell wall reinforcement. A series of events inducing gravity resistance are quite independent of those leading to gravitropism.

Cell Wall↗
PubMed1999

[The use of microfluorimetric analysis for the studies of the influence of changed gravity on isolated lymphocytes in the spleen of the mouse].

Effects of simulated changed gravity on isolated splenetic lymphocytes of mouse were evaluated with the microfluorimetic technique enabling observation of probe fluorescence in individual cells. It was stated that 5 and 60 min of clinostatting stimulated fluorochrome accumulation in cells whereas centrifugation, particularly for 60-minutes, decreased the ability of cells to accumulate fluorescein. Also, alteration of the gravity force had the opposite effect on the ability of cells to retain fluorescein. The most significant drain of the dye immediately after short hypogravity may be indicative of the functional lability of cells during clinostatting. However, as judged by slight changes in intracellular pH, metabolic and regulatory functions were not affected. Hypergravity for 15 min decreased intracellular pH. The increased period of centrifugation stabilized the parameter. Absence of changes in the proliferative activity in all the test exposures also backs up the conclusion that short-term changes in gravity do not produce any substantial shifts in the morphofunctional state of cells in vitro.

Animals↗
PubMed1998

The effects of increased gravity and microgravity on cardiac morphology.

BACKGROUND: Our previous study of rats exposed for 14 d to microgravity on Cosmos 2044 revealed morphological changes consistent with cardiac atrophy. METHODS: In the current comparison study, light and electron microscopic studies were performed on cardiac muscle from 10 rats exposed to hypergravity (continuous centrifugation at 2G) for 14 d. RESULTS: Myofiber area was significantly greater in the 2G papillary muscle as compared with muscle from 10 control rats of the same strain and size. This contrasts with the significant decrease in myofiber area previously seen in the rats exposed to microgravity. At the electron microscopic level, general morphological features were similar in both groups and resembled tissue from control rats from the previous Cosmos studies. However, mitochondria from papillary and ventricular muscle from the 2G rats revealed signs of fatigue typical of the early stage of hypertrophy. These results are consistent with a state of adaptive cardiac hypertrophy for the 2G group.

Adaptation, Physiological↗
PubMed1998

Rat anterior pituitary hormone cells: responses to variable gravity.

BACKGROUND: While life science data dealing with effects of hypogravity are accumulating, relatively little is known about the effects of hypergravity at the level of either the whole animal or the individual cell. The purpose of this experiment was to compare data collected on cells of anterior pituitaries from animals centrifuged at 2G using an experimental design that was identical to that of a spaceflight experiment performed in 1989. HYPOTHESIS: Centrifugation of the animal at 2G for 14 d alters the function and morphology of cells of the anterior pituitary in subsequent in vitro tests at 1G. METHODS: Intact rats were centrifuged at twice Earth's gravity for 14 d in a specially designed animal centrifuge as part of the Cosmos 2G study. This study was designed to replicate a previous spaceflight experiment so that direct comparisons between hyper- (centrifugation, 2G) and hypogravity (spaceflight, 0.001G) could be made. Anterior pituitary cells were then evaluated for cell function and morphology in a variety of post-flight tests. RESULTS: Growth hormone cells from centrifuged animals released less bioactive, but not immunoreactive, growth hormone (GH) than cells from non-centrifuged animals. This was also true for GH released in response to provocative stimulation by a synthetic peptide (growth hormone releasing hormone, GHRH) that causes GH release after binding to cell membrane receptors. Cell morphology was also different between cells from centrifuged and control animals; cells in the experimental group were smaller and less granulated. However, another type of hormone-producing cell contained in these preparations, viz. prolactin cells, was not affected by centrifugation. CONCLUSIONS: Centrifugation of animals for 14 d alters both the in vitro release of GH and GH cell morphology relative to corresponding controls from non-centrifuged animals. Because prolactin cells are not affected by centrifugation, the response is specific to the GH cell.

Animals↗
PubMed2000

[Response of siphoneal alga (Vaucheria sessilis) to the gravity factor].

Growth and development of siphonal alga Vaucheria sessilis under changed gravity and the role of cytoskeletal structures in gravitational response were studied. Hypergravity (3 g) and "hypogravity" were generated by slow clinostating at 7-8 rev/min and rapid clinostating at 35, 70, 135 rev/min, respectively. The experiments in microgravity were flown aboard biosatellite Bion-11. As was shown, V. sessilis responded to changed gravity by inhibition of rate of growth and increasing the number of nuclei in the strand as a result of activation of mitotic processes. Modulation of the course of the gravitational response with anticytoskeletal agents points to involvement of the cytoskeleton. The cortical circuit of actin microfilaments and the cytoplasm stream directed by this structure appear to be the most sensitive to changes in gravity. Gravity-sensitive V. sessilis is another promising object of research in the field of gravitational biology.

Eukaryota↗
PubMed2001

Increased and decreased expression of CD69 and CD23, respectively, in gravity-stressed lymphocytes.

BACKGROUND: Recent studies have shown that gravity-changing stress modulates expression levels of cell surface molecules on human lymphocytes. However, previous in vitro microgravity studies have been performed with lymphocytes treated with mitogenic agents. HYPOTHESIS: The aim of the study was to test if exposure of cells to gravity-changing stress alone alters the expression levels of cell surface molecules. Specifically, we examined whether the expression of activation markers is altered after exposure of lymphocytes to combinations of microgravity and hypergravity. METHODS: We used free-fall in parabolic flight for human subjects and a drop-shaft to expose peripheral blood mononuclear cells (PBMC) to gravity-changing stress. After such exposure, PBMC were isolated, and expression levels of CD69, CD23 and CD38 were estimated using three-color flow cytometry. RESULTS: Increased percentages of CD69-positive cells were observed with PBMC from 3 of 4 volunteers who undertook 10 parabolic flights. Exposure of blood to gravity-changing stress in the drop-shaft increased both ratios of CD69-positive cells and levels of CD69 expression on T and B cells. In contrast, the percentages of CD23-positive B cells was decreased. However, gravity-changing stress was not always followed by significant alteration in CD38 expression. CONCLUSIONS: Our findings suggest that CD69 and CD23 might be useful markers that are up- and down-regulated, respectively, after exposure of lymphocytes to gravity-changing stress.

ADP-ribosyl Cyclase↗
PubMed2001

G-transition effects and their implications.

G-transition effects are defined as the spectrum of physiological and psychophysical effects induced by rapid changes in gravitoinertial forces, alternating between hypogravity (<1 Gz) and hypergravity (>1 Gz) and vice versa. They appear to involve the cardiovascular and spatial orientation systems. This note attempts to briefly review past and current research efforts on the consequences of G-transitions and to examine potential confounding Coriolis-induced bias in both ground-based and inflight research. A brief review of current evidence of vestibular influence on orthostatic compensation and their implications for G tolerance is presented. The effects of roll-induced hypogravity on subsequent G tolerance and possible misperception of attitude during roll rotation are discussed. An integrated approach is recommended for future research on acceleration and disorientation.

Aerospace Medicine↗
PubMed1988

Effect of chronic centrifugation on mouse breeding pairs and their offspring.

Fetuses of chronically centrifuged mice are smaller than 1g fetuses, and have reduced areas of long bone ossification. Fewer pregnancies occurred in centrifuged mice. In this study, exposure of chronically centrifuged females to male bedding 48 hours prior to mating induced estrus as determined by vaginal smears. Females were paired with males on the centrifuge or at 1g, and were sacrificed at 18 days gestation. Fetuses were weighed, measured, and stained with alizarin red and methylene blue. This new mating method increased centrifuge pregnancies, but not to control levels. There were no pregnancies at 3.5 g. Weights and crown rump lengths of centrifuged 18-day fetuses were less than those of controls, significantly so at 2.6 and 2.9g. There was no effect on litter size, number of resorptions per litter or male/female ratio. Bones of centrifuged fetuses were found to be smaller and shaped differently from controls. Effects were mitigated by matings with 1g males. Results confirm our previous reports of decreased fetal size and areas of ossification in hypergravity, and demonstrate a reliable method for providing timed-pregnant mice in hyper-g conditions.

Animals↗
PubMed1993

Changing gravity level and the development of animals.

Space biology has accumulated a great body of information concerning the influence of microgravity upon objects of varying levels of biological organization: from microorganisms to higher animals and humans. However, the choice of biological objects was in most cases random, and there has been no attempt at a comparative biological analysis of the results obtained. A similar situation is noted in hypergravity research, where responses in various animal classes are compared mainly with respect to differences in body masses rather than in the level of biological organization. Without any claims to solve this serious problem in this presentation, I'll try to at least raise it, using as a starting point the conception about evolution of resistance and reactivity, created by my teacher N.N. Sirotinin (1981).

Acceleration↗
PubMed1984

Core temperature of tailless rats exposed to centrifugation.

Although it comprises only about 5% of the total body surface area of the rat, the tail can dissipate about 17% of the animal's body heat. In the present study, we have investigated the role of the tail in the altered thermoregulation of rats during acute hypergravic exposures (achieved by centrifugation). Such exposures produce a rapid fall in core temperature (Tc) leading to a sustained hypothermia. In addition to the Tc changes, there is a significant, but transient increase of tail temperature, indicative of an accelerated rate of heat loss. To determine the extent to which increased heat loss from the tail affects the hypothermic response, rectal temperature changes were measured in both tailless and intact rats subjected to centrifugation. Results from this study indicate that the increased heat loss from the tail per se does not contribute in a measurable way to the hypothermia induced by centrifugation stress.

Aging↗
PubMed1993

The use of centrifugation to study early Drosophila embryogenesis.

By the end of 10th nuclear cycle, the somatic nuclei of the Drosophila embryo have migrated to the periphery of the egg. Centrifugation of embryos did not result in the displacement of these nuclei, since cytoskeletal elements anchor them to the cortex. But, mild centrifugal forces displace the centrally located, nascent yolk nuclei. If this increased sensitivity to hypergravity occurs before the beginning of nuclear differentiation during cycle 8, when the nascent yolk and somatic nuclei physically separate, then it would mark the earliest functional difference between these two lineages.

Animals↗
PubMed1997

[Effects of simulated weightlessness and overweight on the growth of osteoblast cultured in vitro].

A special rotator designed for this experiment was used to simulate the gravitational conditions. 3 groups of osteoblast cells were cultured under simulated hypogravity, normal (1 g) or hypergravity acceleratively (3 g) for 7 d. Changes of cell shape and speed of cell division were observed. The results showed that cells cultured under simulated hypogravity became round and cells divided slowly as compared with 1g group. While cells cultured under 3 g divided more actively and many growth spots appeared in the culture bottle.

Biophysical Phenomena↗
PubMed1993

Swimming velocity of Paramecium under the conditions of weightlessness.

During the 6 min-lasting "free-fall conditions" (4 x 10(-6) g) of the parabolic flight of a sounding rocket Paramecium aurelia cells showed an increase of 7.5 % in their mean swimming velocity. A detailed analysis revealed that the kinetic response was transient: after 3 min the velocity decreased to the speed of the former horizontal swimming at 1 g. Control experiments simulating the influence of vibration and hypergravity during launch of the rocket lead to the conclusion that the increase of the velocity during the parabolic flight was exclusively induced by the transition to 0 g. An increased velocity was also observed under the condition of simulated weightlessness on a fast-rotating clinostat microscope.

Acceleration↗
PubMed1996

Graviresponses in Paramecium biaurelia under different accelerations: studies on the ground and in space.

Behavioural responses to different accelerations below 1 g and up to 5 g were investigated in Paramecium biaurelia by using a centrifuge microscope on Earth and in space during a recent space flight. Increased stimulation (hypergravity) enhanced the negative gravitactic and the gravikinetic responses in Paramecium biaurelia within seconds. Cells did not adapt to altered gravitational conditions. Repetitive stimulation did not change the graviresponses. The minimum acceleration found to induce gravitaxis was between 0.16 and 0.3 g.

Acceleration↗
PubMed1998

Cellular adhesion in neoplastic and syngeneic normal cells under altered gravitational conditions.

The major objective of several experiments performed in space in the last 15 years was to establish whether single cells are sensitive to gravity. It was found in certain cells that reduced gravity leads to profound changes of a number of physiological functions like genetic expression, cell proliferation, signal transduction and cytoskeleton structure. In cell biology studies microgravity can be simulated on Earth in the clinostat. Nearly all data on experiments in the clinostat are related to cells cultured in suspension and, therefore, to adhesion-independent cells. In contrast, several biological phenomena as neoplastic transformation, cell differentiation, in-vitro cellular aging, contact inhibition and cellular adhesion require mainly cellular systems that are adhesion-dependent. The purpose of this work was: a) to study the behaviour of two rat cell strains (neoplastic SGS/4A and syngeneic fibroblasts FG) in order to test whether adhesion-dependent cells are suitable for clinorotation and b) to investigate cell-cell and cell-substratum adhesion in these cells kept under simulated low-g in the fast rotating clinostat and in hypergravity at l0g in the centrifuge.

Animals↗
PubMed1998

Altered gravity modulates 5-lipoxygenase in human erythroleukemia K562 cells.

Mammalian lipoxygenases catalyse the first committed step in the so-called "arachidonate cascade", leading to the production of potent bioactive molecules, such as leukotrienes, lipoxins and hepoxilins. Leukotrienes interact with G protein-couple receptors involved in neuronal plasticity and T lymphocyte activation, lipoxins activate leukocytes, hepoxilines control the insulin release and stimulate the phospholipase C. Lipoxygenase (linoleate:oxygen oxidoreductase; E.C. 1.13.11.34; 5-LOX) are responsible for lymphocyte maturation and programmed death (apoptosis) of neuronal cells. Therefore, 5-LOX might be Space relevant, because among the most striking effects of Space enviroment are indeed those on T lymphocyte activation, neuronal cell growth and suspectedly apoptosis. In this study, the possible effects of the force of gravity on the activity and expression of 5-LOX have been investigated by subjecting human erythroleukemia K562 cells to simulated hypogravity or hypergravity.

Arachidonate 5-Lipoxygenase↗