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At least 343 records · Page 19Linked to original sources
PubMed2003

Suppression of osteoblastic phenotypes and modulation of pro- and anti-apoptotic features in normal human osteoblastic cells under a vector-averaged gravity condition.

Spaceflight and bed rest induce loss of bone mass. A number of in vivo and in vitro studies have been conducted to clarify the mechanisms, however, the results have been conflicting. The purpose of this study was to investigate the effects of gravity unloading on proliferation, phenotypes, and apoptosis of normal human osteoblastic cells in the presence of 1alpha,25-dihydroxyvitamin D3. We used a vector-averaged gravity condition generated by clinostat rotation to simulate gravity unloading. Clinostat rotation did not affect the cell proliferation. On the first day, the mRNA levels for osteocalcin, ALP, CBFA1, VDR, RANKL, and OPG were reduced by clinostat rotation to 21%, 65%, 62%, 52%, 43%, and 54% of control, respectively. ALP activity was decreased to 75% of control. On the second day, the mRNA levels for osteocalcin and RANKL were reduced to 77% and 61% of control, respectively. The decreased VDR mRNA level might be responsible for the reduction for mRNA levels for osteocalcin, RANKL, and OPG. Clinostat rotation increased the pro-apoptotic index (Bax/Bcl-2 ratio) but did not induce apoptosis due to the simultaneous upregulation of the anti-apoptotic XIAP. Reduction of osteoblast responsiveness to 1alpha,25-dihydroxyvitamin D3 might be involved in osteopenia that is induced by gravity unloading.

Alkaline Phosphatase↗
PubMed2002

Gravity sensing in the central nervous system.

For human based space research it is of high importance to understand the influence of gravity on the properties of the central nervous system (CNS). Until now it is not much known about how neuronal tissue can sense gravity. The aim of this study was to find out weather and how the CNS, as a complex system, can percept and react to changes in gravity. Neuronal tissue and especially the CNS fulfils all the requirements for excitable media. Consequently, self-organisation, pattern formation and propagating excitation waves as typical events of excitable media have been observed in such tissue. The spreading depression (SD), an excitation depression wave is the most obvious and best described of these phenomena in the CNS. In our experiments we showed that the properties of the SD and therefore the CNS in its properties as an excitable medium reacts very sensitive to changes in gravity.

Journal Article↗
PubMed2003

Comparison of 3 Methods to Assess Urine Specific Gravity in Collegiate Wrestlers.

OBJECTIVE: To investigate the reliability and validity of refractometry, hydrometry, and reagent strips in assessing urine specific gravity in collegiate wrestlers. DESIGN AND SETTING: We assessed the reliability of refractometry, hydrometry, and reagent strips between 2 trials and among 4 testers. The validity of hydrometry and reagent strips was assessed by comparison with refractometry, the criterion measure for urine specific gravity. SUBJECTS: Twenty-one National Collegiate Athletic Association Division III collegiate wrestlers provided fresh urine samples. MEASUREMENTS: Four testers measured the specific gravity of each urine sample 6 times: twice by refractometry, twice by hydrometry, and twice by reagent strips. RESULTS: Refractometer measurements were consistent between trials (R =.998) and among testers; hydrometer measurements were consistent between trials (R =.987) but not among testers; and reagent-strip measurements were not consistent between trials or among testers. Hydrometer (1.018 +/- 0.006) and reagent-strip (1.017 +/- 0.007) measurements were significantly higher than refractometer (1.015 +/- 0.006) measurements. Intraclass correlation coefficients were moderate between refractometry and hydrometry (R =.869) and low between refractometry and reagent strips (R =.573). The hydrometer produced 28% false positives and 2% false negatives, and reagent strips produced 15% false positives and 9% false negatives. CONCLUSIONS: Only the refractometer should be used to determine urine specific gravity in collegiate wrestlers during the weight-certification process.

Journal Article↗
PubMed1991

Vector-averaged gravity alters myocyte and neuron properties in cell culture.

To investigate whether changes in the gravitational field of developing neurons and myocytes affect cellular development, we rotated cultures of embryonic spinal neurons and myocytes in a horizontal clinostat. Rotation in the clinostat produces, from the cells' perspective, a "vector-free" gravity environment by continuous averaging of the vector. In this way, rotation in the clinostat simulates the microgravity of space where the gravity vector is substantially reduced. At rotation rates of 1-50 rpm, cellular and nuclear areas of myocytes were significantly enlarged and the number of presumptive nucleoli increased. In neurons, frequent and large swellings appeared along neuritic shafts. Some of these changes were reversible after cessation of rotation. Since our data are generally consistent with findings from other cell types subjected to spaceflight, we suggest that the vector-free gravity environment of the clinostat appears to simulate, at least in part, the microgravity of space. Our data further show that cellular processes are sensitive to altered gravity and suggest that cell development in the microgravity of space may be significantly altered.

Animals↗
PubMed1989

[Gravity drainage versus suction drainage: an experimental and clinical study].

The importance of wound drainage in casualty and plastic surgery is unquestioned. The most common form is suction drainage. This involves the disadvantage that the drain can become attached to the tissue by suction, stopping the flow and blocking the drain. In addition, the secretion reservoir must be made of rigid material, which means large package sizes are inevitable. Encouraged by our knowledge of silicone drains, we carried out a study comparing silicone drains (without vacuum) and PVC drains (with vacuum suction). Electron-microscope studies of the PVC drains used for suction drainage revealed adhesion of wound secretion and cell detritus to the inner wall and the drainage perforations after less than 24 h. No occlusion and almost no adherence was observed with silicone gravity drains. When compared in clinical use for joint drainage, neither system had any severe complications. Removal of gravity drains was considerably less painful than withdrawal of suction drains. In soft tissue drainage the volume of secretion drained off was more constant and obviously larger with gravity drainage. From these results we conclude that gravity drainage can replace suction drainage to considerable advantage.

Clinical Trials as Topic↗
PubMedDate not supplied

Evaluation of gravity leukapheresis and comparison with intermittent centrifugation leukapheresis.

Fifteen normal donors underwent gravity leukapheresis using a prototype collection and reinfusion harness after receiving dexamethasone for leukocyte stimulation. A mean of 4.6 units of blood were processed, producing a mean granulocyte yield of 10.8 X 10(9), with an average donation time of 261 minutes. Granulocyte collection efficiency was 79.9 per cent, but yield was only 2.5 X 10(9) granulocytes/hour. Granulocytes obtained by gravity leukapheresis were normal morphologically and had normal bactericidal capacity. Serial determinations showed no changes before and after donation of coagulation profile and serum chemistries in the donors. Seven donors underwent leukapheresis using intermittent centrifugation the day following gravity leukapheresis without further leukocyte stimulation. Mean granulocyte yield (16.1 X 10(9)), and yield/hour (5.37 X 10(9)) of donation were significantly greater for the mechanical method (p less than 0.0005). Gravity leukapheresis required considerable blood bag handling and bag entries, even with the prototype harness. Considering the amount of blood handling, the expense of the sedimenting agent, the probable dose response phenomenon of granulocyte transfusions, and the low yield resulting from the limited volume of blood processed, this technique should not be made widely available, especially where regional centers can provide granulocytes obtained by more productive methods.

Blood Platelets↗
PubMed1995

Gravity effect on lymphocyte deformation through cell shape change.

The effects on human cells (lymphocyte) immersed in a culture liquid under microgravity environment has been investigated. The study was based on the numerical simulation of the Morphology of human cells affected by the time dependent variation of gravity acceleration ranging from 10(-3) to 2 g(o) (g(o) = 9.81 m/s2) in 15 s. Both the free floating cells and the cells which came into contact with the upper and lower inclined walls imposed by the time-dependent reduced gravity acceleration were considered in this study. The results show that, when the gravity acceleration increased, the cell morphology changed from spherical to horizontally elongated ellipsoid for both the free floating cells and the stationary cells on the lower inclined wall while the cell morphology varied from spherical to vertically-elongated ellipsoid for the cells hanging on the upper inclined wall. A test of the deformation of human cells exposed to the variation of gravity levels, carried out in the KC-135 free fall aircraft, show that the results of experimental observations agree exactly with the theoretical model computation described in this paper. These results will be useful for study of the behavior and morphology of cells in space.

Cell Size↗
PubMed1995

A novel variable-gravity simulation method: potential for astronaut training.

Zero gravity conditions for astronaut training have traditionally used neutral buoyancy tanks, and with such tanks hypogravity conditions are produced by the use of supplemental weights. This technique does not allow for the influence of water viscosity on any reduced gravity exercise regime. With a water-foam fluid produced by using a microbubble air flow together with surface active agents to prevent bubble agglomeration, it has been found possible to simulate a range of gravity conditions without the need for supplemental weights and additionally with a substantial reduction in the resulting fluid viscosity. This new technique appears to have application in improving the simulation environment for astronaut training under the reduced gravity conditions to be found on the moon or on Mars, and may have terrestrial applications in patient rehabilitation and exercise as well.

Astronauts↗
PubMed1996

An evaluation of two methods used to determine the centre of gravity of a cadaver head in the sagittal plane.

A suitable method to locate the centre of gravity of the head is not available at present. Precise location of that centre will help in the understanding of aspects of cranial balance and what effect skeletal changes, following for example orthognathic surgery, may have on head posture. The objective of this research was to use a mechanical (empirical) method, based on accepted laws of physics, to determine the centres of gravity of cadaver heads in the sagittal plane and to compare these positions with those generated by a computer programme. The two methods located the centre of gravity in the same region but at a different position in each corresponding head. These differences were statistically significant (p < 0.01). It is likely that improved computer techniques together with modern three dimensional imaging methods will be able to locate the centre of gravity of a head in a living subject.

Cadaver↗
PubMed1996

Influence of altered gravity on the cytochemical localization of cytochrome oxidase activity in central and peripheral gravisensory systems in developing cichlid fish.

Cichlid fish larvae were reared from hatching to active free swimming under different gravity conditions: natural environment, increased acceleration in a centrifuge, simulated weightlessness in a clinostat and near weightlessness during space flight. Cytochrome oxidase activity was analyzed semiquantitatively on the ultrastructural level as a marker of regional neuronal activity in a primary, vestibular brainstem nucleus and in gravity receptive epithelia in the inner ear. Our results show, that gravity seems to be positively correlated with cytochrome oxidase activity in the magnocellular nucleus of developing fish brain. In the inner ear the energy metabolism is decreased under microgravity concerning utricle but not saccule. Hypergravity has no effect on cytochrome oxidase activity in sensory inner ear epithelia.

Animals↗
PubMed1972

OFO experimental techniques and preliminary conclusions: is artificial gravity needed during prolonged weightlessness?

The technique of single unit recording from body systems generating electrical pulses coherent with their basic function (CNS, muscles, sense organs) has been proved feasible during the OFO A orbital flight, an automatic physiological experiment. All microelectrode implants survived the lift off of a Scout vehicle. The far-reaching impact of such a technique in biological space research and in the laboratory is discussed. The results of recording 155 hours of orbital flight of pulses from the nerve fibres of four vestibular gravity sensors in two bull frogs indicate that the vestibular organ adjusts to zero g. As all the other biological changes observed during orbit are due to lack of exercise, it is concluded that artificial gravity might not be necessary during prolonged space missions or on low gravity celestial bodies.

Animals↗
PubMed1987

The response to medical litholytic treatment of gallstones according to their specific gravity.

The buoyancy of gallstones was observed by taking anterior-posterior scout X-ray films of two patients standing during endoscopic retrograde cholangiography. In case 1, the large and small gallstones differed in buoyancy, and ursodeoxycholic acid treatment dissolved the floating small stones while failing to dissolve the nonfloating large stone. In case 2, both the large and small stones floated and are being dissolved by ursodeoxycholic acid treatment. Since floating or nonfloating and the plane of flotation depend on the specific gravity of the gallstone, the above findings suggest that a gallstone with a low specific gravity is more readily dissolved than one with a high specific gravity. The present method of estimating the buoyancy of gallstones was therefore considered extremely useful in selecting patients for medical litholytic treatment.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1986

Perception of gravity in the lentil root.

The gravisensing cells (statocytes), responsible for the perception of gravity, are located in the center of the root cap. The statocytes contain voluminous amyloplasts (statoliths) which are capable of moving in the direction of gravity. The sedimentation of the amyloplasts is due to the starch grains, which are much denser than the surrounding cytoplasm. When the starch of these plastids is removed, the statoliths lose their mobility and the roots are no longer able to respond to gravity. When the roots grow in their normal position, the statoliths are sedimented on large aggregates of endoplasmic reticulum. The role of the association between these two types of organelles is still controversial. For some authors, the amyloplast-endoplasmic reticulum complex would play a role in the induction of the gravitropic response. For other authors, this complex would regulate gravitropic curvature and is more likely to be involved in the termination of the response. The goal of the 39F experiment (Biorack) was to dissociate this complex by growing lentil roots in microgravity and to stimulate them on a centrifuge in order to determine if they were still capable of curvature.

Cell Polarity↗
PubMed1984

Relationship between specific gravity, water content, and serum protein extravasation in various types of vasogenic brain edema.

Vasogenic brain edema was induced in cats by cold injury (six animals), brain tumors (five animals), and brain abscesses (six animals). Water and electrolyte content, specific gravity, blood volume, and the amount of extravasated serum proteins were determined in small tissue samples taken from gray and white matter at various distances from the lesion. Edema was strictly confined to the white matter of the affected hemisphere and declined from the lesion to the more peripheral regions. It was characterized by the extravasation of serum proteins and an increase of water and sodium content with little or unpredictable changes of potassium and blood volume. The calculated sodium content of edema fluid varied between 129 and 135 mueq/ml, and serum protein content between 8.1 and 11.9 mg/ml. In all three types of edema, specific gravity and water content correlated closely with the same slope and intercept of the calculated regression (y = 1.119-0.0011 x, r = -0.91). The results obtained indicate that the main denominator of specific gravity of edematous white matter is water content and that this relationship is not significantly altered by variations of blood volume or serum protein content.

Animals↗
PubMed1992

[Research under reduced gravity. Part II: experiments in variable gravitational fields].

Recently, the reduced gravitational field of space laboratories, rockets, or satellites in Earth orbits offers a gravitational field which is variable from 10(-4) g to 1 g by the use of centrifuges. Especially with plants, data concerning gravisensitivity are based on experiments with clinostats. First experiments in reduced gravitational fields, however, demonstrate the uncertainty of these results. Thus, the main task of gravitational biologists is to test the validity of results obtained with the aid of clinostats. On this basis it should be possible to find a common mechanism to explain the influence of gravity on organisms. Experiments under reduced gravity in sounding rockets provided new knowledge on the perception of the gravity stimulus in plant cells.

Biological Science Disciplines↗
PubMed1975

Determination of the glomerular filtration rate by the minute diuresis at a specific gravity of 1001.

A new method is described for determination of the glomerular filtration rate, based on the fact that at an urinary specific gravity of 1001 the final urine is concentrated 6.67 times, as compared with the primary glomerular filtrate. The glomerular filtration rate is evaluated by multiplication of the minute diuresis at a specific gravity of 1001 by the factor 6.67. In this manner the chemical analysis of urine and blood is avoided. Urine with a specific gravity of 1001 is obtained by water loading much the same as in the dilution test of Volhard. For checking the accuracy of the method, comparative studies were conducted with creatinine clearance in 36 patients and with 51Cr-EDTA clearance in 33 patients. The difference in the values of the glomerular filtration rate, evaluated by the above-mentioned two methods and the new method was statistically not significant (p greater than 0.05). The method is recommended for the early detection of disturbances in the glomerular function prior to the occurrence of azotemia.

Diuresis↗
PubMed2006

Effect of gravity in long-term vitreous tamponade: in vivo investigation using perfluorocarbon liquids and semi-fluorinated alkanes.

PURPOSE: In order to investigate whether gravity is the reason for retinal degeneration in long-term vitreous tamponade, perfluorohexyloctane (F6H8), perfluorodecalin (PFD), and a mixture of F6H8/PFD were compared. MATERIALS AND METHODS: Each group of 5 rabbits received a 3-month tamponade with either PFD (pure) (1.93 g/cm(3)), F6H8 (pure) (1.33 g/cm(3)), or a 1:1 mixture of F6H8/PFD (1.62 g/cm(3)). Electroretinograms (ERG) were performed pre- and postoperatively. Lower and upper retinal areas were compared using immunohistochemical methods. Transmission electron microscopy was performed to investigate alterations in the photoreceptors. RESULTS: All three substances were tolerated well in rabbit eyes for up to 3 months. Dispersion was seen earliest with PFD and latest with pure F6H8. None of the substances demonstrated inflammatory reactions or vascular alterations. ERGs were not considerably altered with any of the substances. Histology of the retina showed alterations in the cell counts within the inner and outer nuclear layer that were not attributable to the gravity of the tamponading agent. CONCLUSION: In contrast to previously published work, this study did not detect any tamponade-related structural damage of the retina after a 3-months tamponade in the rabbit model. Based upon this study, we conclude that gravity might not be causally linked to retinal damage.

Animals↗
PubMed2006

Gravity-induced absorption changes in Phycomyces blakesleeanus during parabolic flights: first spectral approach in the visible.

Gravity-induced absorption changes as experienced during a series of parabolas on the Airbus 300 Zero-G have been measured previously pointwise on the basis of dual-wavelength spectroscopy. Only the two wavelengths of 460 and 665 nm as generated by light-emitting diodes have been utilised during our first two parabolic-flight campaigns. In order to gain complete spectral information throughout the wavelength range from 400 to 900 nm, a miniaturized rapid scan spectrophotometer was designed. The difference of spectra taken at 0 g and 1.8 g presents the first gravity-induced absorption change spectrum measured on wild-type Phycomyces blakesleeanus sporangiophores, exhibiting a broad positive hump in the visible range and negative values in the near infrared with an isosbestic point near 735 nm. The control experiment performed with the stiff mutant A909 of Phycomyces blakesleeanus does not show this structure. These results are in agreement with those obtained with an array spectrophotometer. In analogy to the more thoroughly understood so-called light-induced absorption changes, we assume that gravity-induced absorption changes reflect redox changes of electron transport components such as flavins and cytochromes localised within the plasma membrane.

Absorption↗