SEARCH · PubMed Health

Results for “GRAVITATION”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources

PubMedDate not supplied

Modified gravitational field and lactate dehydrogenase activity.

The paper deals with the effects of the gravitational field investigated either by hypokinesia with corresponding diminution of muscle solicitation, or by centrifugation, that is by rise of gravitational solicitation, on lactate dehydrogenase activity of rats. After 7 days of hypokinesia the activity of lactate dehydrogenase is significantly changed by the elevation of LDH5 isoenzyme, both in serum and in myocardium. The enhancement is by 40% in serum and by 30% in myocardium against the control group. In centrifuged rats the enhancement of LDH5 isozyme is much lesser than in hypokinetic rats, that is by 18% in myocardium and by 20% in serum against the control group. The total of all LDH1-5 isozymes was found in cardiac muscle of both hypokinetic, centrifuged and control group. In serum only two fractions LDH2 and LDH5 isozymes appear both in hypokinetic, centrifuged and control group.

Adrenalectomy↗

PubMed1981

[Effect of artificial gravitation during space flight on motor habit retention in white rats].

The recovery of a goal-reaching habit (food reaching) was studied in albino rats in a maze after space exposure on biosatellite "Kosmos-936". Animals which were exposed to artificial gravitation during the flight, restored the habit slightly worse than those not centrifuged. The tendency toward worsening is clearly pronounced, although the small number of animals and small changes (which to a considerable degree was due to relatively simple tasks) seem to produce insignificant differences at this stage of the study. The absence of positive effect of artificial gravitation might be connected with a negative effect of angular speeds during centrifugation.

Animals↗

PubMed1976

[Effect of gravitational stresses on morphologic changes in the lymphatic bed of the guinea pig cecum during blockade of M-cholinoreactive systems].

The work has been performed in the material taken from 40 quinea pigs whose lymphatic bed was injected by Gerota's mass. The material was treated by macro-microscopical methods and the method of luxmetry. A single exposure to gravitation stress of ventro-dorsal direction caused probounced morphological changes in all links of the lymphatic bed of the guinea pig's coecum. Exclusion of the central and peripheral M-cholinoreactive systems of the organism by means of scopolamin in doze 50 mkg/kg had a protecting effect on the coecum lymphatic bed in the following exposure to gravitation stress.

Animals↗

PubMed1977

[Influence of preliminary conditioning to gravitational overloading and subsequent exposure to a series of extreme factors on the intra-organ blood flow of the intestine].

The intraorganic blood circulation bed of the intestine was studied in 21 rabbits subjected to training to gravitation stresses (according to special schedules) and then to maximum endurable gravitation stresses, hypokinesia for 4 weeks and repeated stresses of the direction and character similar to those at the beginning of the experiment. The direction of stresses was different: head--pelvis, pelvis--head, chest--back. Injection of the intestine blood vessels with the Gerota's mass followed by clearing after A. M. Malygin, histological staining after Van Gieson and method of luxmetry were used. Preliminary training to stresses considerably prevented anatomical alterations in blood vessels of the intestinal coats. The most favourable morphological picture was observed in the cases when the stress was of ventro-dorsal direction. Blood vessels of the large intestine were more inert in their transformation than those of the small intestine coats.

Adaptation, Physiological↗

PubMed1998

[Drawing movements and gravitational force: central or peripheral regulation?].

Drawing arm movements in four different directions: a) upward vertical (0 degree), b) upward oblique (45 degrees), c) downward vertical (180 degrees) and d) downward oblique (135 degrees), and at two different speeds, normal and fast, were executed by eight subjects. Movements of the arm were recorded using an optoelectronic (2 TV, 100 Hz) system which allowed the computer reconstruction of joint motion. Analyses focused upon pen kinematics in the frontal plane. Velocity profiles were unimodal for all conditions. The ratio of acceleration time to total movement time changed significantly as a function of the direction and the speed of the movement. Movement time and was not affected by movement direction and consequently changes in gravitational torques, for both speeds tested. Results from this study provide indirect evidence that the CNS executes movements by taking advantage of gravitational force.

Adult↗

PubMed2006

Modeled gravitational unloading triggers differentiation and apoptosis in preosteoclastic cells.

Gravity acts permanently on organisms as either static or dynamic stimulation. Understanding the influence of gravitational and mechanical stimuli on biological systems is an intriguing scientific problem. More than two decades of life science studies in low g, either real or modeled by clinostats, as well as experimentation with devices simulating different types of controlled mechanical stimuli, have shown that important biological functions are altered at the single cell level. Here, we show that the human leukemic line FLG 29.1, characterized as an osteoclastic precursor model, is directly sensitive to gravitational unloading, modeled by a random positioning machine (RPM). The phenotypic expression of cytoskeletal proteins, osteoclastic markers, and factors regulating apoptosis was investigated using histochemical and immunohistochemical methods, while the expression of the corresponding genes was analyzed using RT-PCR. A quantitative bone resorption assay was performed. Autofluorescence spectroscopy and imaging were applied to gain information on cell metabolism. The results show that modeled hypogravity may trigger both differentiation and apoptosis in FLG 29.1 cells. Indeed, when comparing RPM versus 1 x g cultures, in the former we found cytoskeletal alterations and a marked increase in apoptosis, but the surviving cells showed an osteoclastic-like morphology, overexpression of osteoclastic markers and the ability to resorb bone. In particular, the overexpression of both RANK and its ligand RANKL, maintained even after return to 1 x g conditions, is consistent with the firing of a differentiation process via a paracrine/autocrine mechanism.

Apoptosis↗

PubMed2005

Do novel gravitational environments alter the grip-force/load-force coupling at the fingertips?

In this experiment we examined the coupling between grip force and load force observed during cyclic vertical arm movements with a hand-held object, performed in different gravitational environments. Six subjects highly experienced in parabolic flight participated in this study. They had to continuously move a cylindrical object up and down in the different gravity fields (1g, 1.8 g and 0 g) induced by parabolic flights. The imposed movement frequency was 1 Hz, the object mass was either 200 or 400 g, the amplitude of movement was either 20 or 40 cm and an additional mass of 200 g could be wound around the forearm. Each subject performed the task during 15 consecutive parabolas. The coordination between the grip force normal to the surface and the tangential load force was examined in nine loading conditions. We observed that the same normal grip force was used for equivalent loads generated by changes of mass, gravity or acceleration despite the fact that these loads required different motor commands to move the arm. Moreover, our results suggest that the gravitational and inertial components of the load are treated adequately and independently by the internal models used to predictively control the required grip force. These results indicate that the forward internal models used to control precision grip take into account the dynamic characteristics of the upper limb, the object and the environment to predict the object's acceleration and, in turn, the load force acting at the fingertips.

Adult↗

PubMed2005

Gravitational influences on reference frames for mapping somatic stimuli in brain-damaged patients.

Previous studies have shown that the manipulation of body position in space can modulate the manifestations of visual neglect. Here, we investigated in right brain-damaged patients (RBD) the possible influence of gravitational inputs on the capability to detect tactile stimuli delivered to hands positioned in ipsilesional or contralesional space. RBD patients (with or without impairments in detecting contralesional stimuli under single and double stimulation conditions) and healthy control subjects were tested in a tactile detection task in which gravitational (upright vs. supine) and hand position (anatomical vs. crossed) variables were orthogonally varied. The postural manipulation of the entire body turned out to influence the degree of tactile detection. In particular, RBD patients with tactile deficits detected a significantly higher number of left-sided stimuli in the supine posture than in the upright posture. Moreover, crossing of hands improved the ability of RBD patients with tactile deficits in detecting stimuli delivered to their left contralesional hand. The beneficial effect of lying supine was independent of the spatial position of the hands, thus suggesting that the improvement of performance dependent upon entire-body posture and that dependent upon crossing hands may rely upon separate mechanisms.

Aged↗

PubMed2003

Changes in gravitational forces induce modifications of gene expression in A. thaliana seedlings.

By comparing the expression patterns of selected genes from Arabidopsis thaliana (L.) Heynh. grown either at 1 g or on a clinostat (horizontally or vertically inverted, 1 rpm), and either used directly or after hypergravity stimulation, we have shown that the pattern of expression did not proceed in a stereotypical manner. Rather, the selected genes fell into different classes. These classes include (i) those insensitive to the gravitational conditions, (ii) those that are regulated in an opposite manner by hypergravity and clinostat conditions, (iii) those that are desensitised to hypergravity by long-term culture on a clinostat, and (iv) those enhanced by such a treatment. Our data suggest that rapid reorientation of gene expression is likely to occur in response to changes in the gravitational conditions.

Arabidopsis↗

PubMed1991

Isolation of microfilariae from blood by gravitational field-flow fractionation.

Over 100 million persons suffer from diseases caused by filariae infestation, and one billion are at risk. A simple isolation method for both analytical and preparative separation is presented. Based on the simplest field-flow fractionation technique, the gravitational one, effective isolation of microfilariae is achieved. Microfilariae are eluted in the void volume of the channel without pollution by red blood cells. The red blood cell elution peak shows a total absence of microfilariae, as demonstrated after fraction collection and microscopic investigation. The elution mode of microfilariae and red blood cells appears to be a steric one, as confirmed by a reinjection experiment. The simplicity, low cost and the relatively short time required for this separation (10 min) indicate that gravitational field-flow fractionation could become a new separation tool for screening of microfilariae. With both live and dead microfilariae, the high recovery (66-80%) allows preparative fractionation for diagnostic purposes or fundamental research.

Animals↗

PubMed2006

Irreversible morphological changes in leg bone following chronic gravitational unloading of growing rats.

Effects of gravitational unloading or loading on the growth and development of hindlimb bones were studied in rats. Male Wistar rats were hindlimb-unloaded or loaded at 2-G from the postnatal day 4 to month 3. The morphology and mineral content of tibia and fibula, as well as the mobility of ankle joints, were measured at the end of 3-month suspension or loading, and 1, 2, and 3 months after ambulation recovery. Growth-related increases of bone weight and mineral density were inhibited by unloading. But they were gradually recovered toward the control levels, even though they were still less than those in the age-matched controls after 3 months. None of the parameters were influenced by 2-G loading. However, here we report that chronic unloading causes abnormal morphological development in hindlimb bone of growing rats. Irreversible external bend of the shaft and rotation of the distal end of tibia, which limit the dorsiflexion of ankle joints, were induced following chronic gravitational unloading during developing period. It is also suggested that such phenomena are caused by the abnormal mechanical forces imposed by muscle utilization with altered patterns. The activity of ankle dorsiflexor was increased and that of plantarflexor was inhibited during unloading.

Animals↗

PubMed2005

Development as adaptation: a paradigm for gravitational and space biology.

Adaptation is a central precept of biology; it provides a framework for identifying functional significance. We equate mammalian development with adaptation, by viewing the developmental sequence as a series of adaptations to a stereotyped sequence of habitats. In this way development is adaptation. The Norway rat is used as a mammalian model, and the sequence of habitats that is used to define its adaptive-developmental sequence is (a) the uterus, (b) the mother's body, (c) the huddle, and (d) the coterie of pups as they gain independence. Then, within this framework and in relation to each of the habitats, we consider problems of organismal responses to altered gravitational forces (micro-g to hyper-g), especially those encountered during space flight and centrifugation. This approach enables a clearer identification of simple "effects" and active "responses" with respect to gravity. It focuses our attention on functional systems and brings to the fore the manner in which experience shapes somatic adaptation. We argue that this basic developmental approach is not only central to basic issues in gravitational biology, but that it provides a natural tool for understanding the underlying processes that are vital to astronaut health and well-being during long duration flights that will involve adaptation to space flight conditions and eventual re-adaptation to Earth's gravity.

Adaptation, Physiological↗

PubMed2004

Effects of deafferentation on the size and myosin phenotype of muscle fibers on stretching of the rat soleus muscle in conditions of gravitational unloading.

The aim of the present work was to assess the contributions of the reflex and local components to preventing decreases in the size and changes in the ratio of fibers containing the slow and fast isoforms of myosin heavy chains during chronic stretching of a postural muscle in rats in conditions of gravitational unloading. A unilateral surgical deafferentation method was used. The results demonstrated that deafferentation of the hindlimb had no effect on preventing reductions in muscle fiber size in conditions of chronic muscle stretching in conditions of gravitational unloading. The results obtained from these experiments did not support the hypothesis that the predominant contribution to preventing the development of atrophic changes comes from activation of muscle afferents in chronic stretching of the unloaded muscle. Deafferentation of both suspended animals and those with normal motor activity led to increases in the proportion of soleus muscle fibers containing the slow isoforms of myosin heavy chain.

Animals↗

PubMed2000

Detection of weak gravitational lensing distortions of distant galaxies by cosmic dark matter at large scales

Most of the matter in the Universe is not luminous, and can be observed only through its gravitational influence on the appearance of luminous matter. Weak gravitational lensing is a technique that uses the distortions of the images of distant galaxies as a tracer of dark matter: such distortions are induced as the light passes through large-scale distributions of dark matter in the foreground. The patterns of the induced distortions reflect the density of mass along the line of sight and its distribution, and the resulting 'cosmic shear' can be used to distinguish between alternative cosmologies. But previous attempts to measure this effect have been inconclusive. Here we report the detection of cosmic shear on angular scales of up to half a degree using 145,000 galaxies and along three separate lines of sight. We find that the dark matter is distributed in a manner consistent with either an open universe, or a flat universe that is dominated by a cosmological constant. Our results are inconsistent with the standard cold-dark-matter model.

Journal Article↗

PubMed2002

Gravitationally redshifted absorption lines in the X-ray burst spectra of a neutron star.

The fundamental properties of neutron stars provide a direct test of the equation of state of cold nuclear matter, a relationship between pressure and density that is determined by the physics of the strong interactions between the particles that constitute the star. The most straightforward method of determining these properties is by measuring the gravitational redshift of spectral lines produced in the neutron star photosphere. The equation of state implies a mass-radius relation, while a measurement of the gravitational redshift at the surface of a neutron star provides a direct constraint on the mass-to-radius ratio. Here we report the discovery of significant absorption lines in the spectra of 28 bursts of the low-mass X-ray binary EXO0748-676. We identify the most significant features with the Fe XXVI and XXV n = 2-3 and O VIII n = 1-2 transitions, all with a redshift of z = 0.35, identical within small uncertainties for the respective transitions. For an astrophysically plausible range of masses (M approximately 1.3-2.0 solar masses; refs 2-5), this value is completely consistent with models of neutron stars composed of normal nuclear matter, while it excludes some models in which the neutron stars are made of more exotic matter.

Journal Article↗

PubMed2005

The formation of stars by gravitational collapse rather than competitive accretion.

There are two dominant models of how stars form. Under gravitational collapse, star-forming molecular clumps, of typically hundreds to thousands of solar masses (M(o)), fragment into gaseous cores that subsequently collapse to make individual stars or small multiple systems. In contrast, competitive accretion theory suggests that at birth all stars are much smaller than the typical stellar mass (approximately 0.5M(o)), and that final stellar masses are determined by the subsequent accretion of unbound gas from the clump. Competitive accretion models interpret brown dwarfs and free-floating planets as protostars ejected from star-forming clumps before they have accreted much mass; key predictions of this model are that such objects should lack disks, have high velocity dispersions, form more frequently in denser clumps, and that the mean stellar mass should vary within the Galaxy. Here we derive the rate of competitive accretion as a function of the star-forming environment, based partly on simulation, and determine in what types of environments competitive accretion can occur. We show that no observed star-forming region can undergo significant competitive accretion, and that the simulations that show competitive accretion do so because the assumed properties differ from those determined by observation. Our result shows that stars form by gravitational collapse, and explains why observations have failed to confirm predictions of the competitive accretion model.

Journal Article↗

PubMed1997

Dynamics of a pair of spherical gravitating shells.

The dynamical N body problem for a system of mass points interacting solely through gravitational forces is not integrable. The difficulties which arise in constructing accurate numerical codes for simulating the motion over long time scales are legend. Thus, in order to test their theories, astronomers and astrophysicists resort to simpler, one-dimensional models which avoid the problems of binary formation, escape, and the singularity of the inverse square force law. To date, the most frequently employed "test" model consists of a system of parallel mass sheets moving perpendicular to their surface. While this system avoids all of the above problems, the time scale for reaching equilibrium is extremely long and probably arises from the system's weak ergodic properties, which become manifest even in the three sheet system. Here we consider a different one-dimensional gravitating system consisting of nonrotating concentric mass shells. For the case of two shells we investigate the structure of the phase space by studying the stability of periodic trajectories. By employing an event driven algorithm, we are able to directly investigate the influence of the singularity without having to resort to regularization of the force. Although stable structures are present at every energy, we find that the ergodic properties of this system are more robust than its planar counterpart. (c) 1997 American Institute of Physics.

Journal Article↗

PubMed1999

Dynamics of a gravitational billiard with a hyperbolic lower boundary.

Gravitational billiards provide a simple method for the illustration of the dynamics of Hamiltonian systems. Here we examine a new billiard system with two parameters, which exhibits, in two limiting cases, the behaviors of two previously studied one-parameter systems, namely the wedge and parabolic billiard. The billiard consists of a point mass moving in two dimensions under the influence of a constant gravitational field with a hyperbolic lower boundary. An iterative mapping between successive collisions with the lower boundary is derived analytically. The behavior of the system during transformation from the wedge to the parabola is investigated for a few specific cases. It is surprising that the nature of the transformation depends strongly on the parameter values. (c) 1999 American Institute of Physics.

Journal Article↗