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At least 703 records · Page 39Linked to original sources
PubMed1996

The effect of gravity on plant germination.

An axis clinostat was constructed to create micro and negative gravity also a rotated flat disk was constructed with different rotation rates to give increased gravity, by centrifugal force up to 48 g. Rice seeds were grown on agar in tubes at the constant air temperature of 20 degrees C under an average light condition of 110 micromol/m2/sec(PPF). Humidity was not controlled but was maintained above 90%. Since the tube containers were not large enough for long cultivation, shoot and root growth were observed every 12 hours until the sixth day from seeding. The lengths of shoots and roots for each individual plant were measured on the last day. The stem lengths were increased by microgravity but the root lengths were not. Under the negative gravity, negative orthogeotropism and under microgravity, diageotropism was observed. No significant effect of increased gravity was observed on shoot and root growth.

Centrifugation↗
PubMed1974

Haemodynamic changes caused in rats by prolonged accelerations.

Experiments were performed on 60 rats undergoing about 5 Gz acceleration. The animals were killed in liquid nitrogen at various times after centrifugation (time of centrifugation 1 hour). Before centrifugation 131I-labelled albumin was injected intravenously and after the experiment radioactivity of muscles from the extremities was measured. The following conclusions were drawn from the experiments: (i) About 5 Gz acceleration in the longitudinal axis results in blood displacement to the hind limbs with extravascular leakage of albumin. (ii) Immediately after centrifugation lowering of blood amount in the hind limbs occurred. During the first 15 minutes this decrease progresses very quickly, while later it is much smaller. Nevertheless even 3 hours after centrifugation there was only partial return to normality. (iii) Transudation of albumin in the hind limbs lasts a few hours after centrifugation. (iv) The haemodynamic changes caused by centrifugation consist of blood stasis and extravascular leakage of proteins.

Acceleration↗
PubMed1974

Metabolic responses of monkeys to increased gravitational fields.

A depletion of body fat has been reported by several investigators for various species of homoiotherms exposed to chronic acceleration. Generally the effect is proportional to field strength, and over the size range examined (0.25-5 kg) it becomes more severe in larger animals. There is some evidence that this may be the result of increased secretion of a pituitary hormone, the fat mobilizing substance (FMS). An exception to the defatting effect of chronic acceleration was observed in mature pig-tailed monkeys (Macaca nemestrina)--although they exhibited other changes generally found in homoiotherms exposed to hyperdynamic environments. It is considered that this unusual primate response to chronic acceleration may result from a different geometry of the central nervous system, and its effect upon gravity load distribution in the lower part of the brain.

Acceleration↗
PubMed1974

Gravitational stress and exercise.

This paper deals with the influence of G forces on certain circulatory and metabolic adjustments to dynamic exercise. Leg exercise in the sitting position increases systemic mean pressure both at normal and at increased G, thus improving G tolerance. When the force of gravity is increased to three times its normal value, leg exercise produces a much more marked increment in stroke volume than in heart rate, which contrasts with the case at normal gravity. Beta-adrenergic blockade, which strongly inhibits the heart rate response to gravitational stress, but leaves the systemic mean pressure and G tolerance unaffected, exaggerates the dominance of the stroke volume increase in exercise at increased G. With leg exercise at increasing work loads at 3G, the O2 uptake tends to level off and the arterial lactates to rise at a lower load than at normal gravity, indicating that the upper limit for the O2 uptake is lowered by the G force. A progressive increase of the venous admixture in the lungs suggests that the primary limitation of the O2 transport occurs in the pulmonary gas exchange.

Adrenergic beta-Antagonists↗
PubMed1974

The role of gravity in the phylogeny of structure and function in animal sensors of spatial orientation, and their predicted action in weightlessness.

The evolution of the structural, functional and cytochemical organization of the gravity receptor which determines a body position in the gravitational field of the earth by means of muscular regulation was traced both invertebrates and vertebrates, using electron microscopic and histochemical methods. In the course of evolution of vertebrates, the specialized gravity receptor-statocyst which, as a rule, consists of primary sensory cells and supplies otoliths, is formed. In vertebrates, there exists a vestibular apparatus made up of secondary sensory cells and also having otoliths. The receptor cells, both of statocysts and the vestibular apparatus, are supplied with special antennas (kinocilia and stereocilia). Deviation of the antennas stimulated by displacement of the otoliths resulting from locomotor activity of animals leads to excitation of the receptor cells. When exposed to a modified gravitational field (linear accelerations of 10 g, for 3 min), the receptor cells of the vestibular apparatus, in all classes of vertebrates, show progressive changes in RNA content and protein synthesis (increase followed by decrease) which return to normal only after 12 days. Thus, immediate transfer of animals and man from acceleration to weightlessness appears to be a reason for movement disease. The above consideration showed the need for an experiment in which an animal (with its vestibular apparatus) which had not undergone previous accelerations, would be exposed to weightlessness. Frog embryos, Rana temporaria, at the stage preceding the organogenesis, when the vestibular apparatus and other organs were lacking, were chosen as a suitable subject. Frog embryos at the stage of an early gastrula were placed in a special container Emkon aboard the Soyuz 10 spacecraft. After short accelerations, they were exposed to weightlessness for 44 hours. The embryos were allowed to continue to develop to the stage of early tail bud. The experimental embryos showed normally developed acoustic vesicles and vestibular ganglia. Clear differentiation of the receptor cells with antennas (kinocilia and stereocilia) was found in the acoustic vesicles. Thus, in weightlessness, vestibular apparatus develops just as well as in the gravitational field of the earth. However, only a much longer stay in weightlessness conditions will indicate whether there are any changes in the structural, cytochemical and functional organization of vestibular apparatus. The similarity in the structural, functional and cytochemical organization of the gravity receptor in vertebrates and invertebrates appears to allow the prediction of the behaviour of the gravity receptor as a whole, and of its receptor elements, both in normal and changed gravitational fields. The first attempts were carried out only on the vestibular apparatus of vertebrates.

Acetylcholinesterase↗
PubMed1978

Changes in the body composition of monkeys during long-term exposure to high acceleration fields.

Adult, 10-14 kg, male pig-tailed monkeys (Macaca nemestrina) were subjected to continuous centrifugation for 7 months in acceleration fields up to 2.5 g. Several major parameters of body composition, body-fluid distribution, and hematology were evaluated at various levels of high g by in vivo analytical techniques. Statistically significant decreases in total body mass, lean body mass, total body water, extracellular water content and interstitial water content proportional to the level of high g were also demonstrated. Body cell mass, total body fat, dry body mass, lean body solids, and red cell volume did not change significantly. Significant decreases in red cell count, blood hemoglobin level and venous hematocrit value accorded with the plasma volume and red cell volume findings. Total plasma protein concentration did not change significantly. The results indicate a substantial loss of total body mass in the form of body water. The loss apparently occurred from the interstitial spaces of the body in the face of a sizeable increase in plasma volume. Physiological significance of the body composition and fluid distribution changes at high g is discussed and compared to the changes described for astronauts at low g. Current theory of fluid-balance physiology favors the concept that interstitial volume and blood volume are tightly coupled and change in the same direction. However, it appears that the changes which occur where the ambient acceleration field is varied may represent an exception to the general hypothesis for the regulation of the extracellular fluid volume.

Acceleration↗
PubMed1978

Thermoregulatory responses of unanesthetized rats exposed to gravitational fields of 1 to 4g.

Rats exposed to 2g environments (achieved by centrifugation) exhibit a decreased ability to maintain colonic temperature (Tco) when challenged with a 1 hr drop in ambient temperature (Ta). As an extension of this work the present study considers whether the altered ability to maintain Tco is proportional to the magnitude of the acceleration field in the range from 1g-4g, and whether the magnitude of the decreased thermoregulatory ability is related to the onset time of the temperature drop relative to that of the acceleration. Male, Sprague-Dawley rats were instrumented on the experimental day with thermistors for measuring Tco. The unanesthetized rat was then placed in a plexiglas chamber, positioned on a centrifuge 1.37 m in radius, and exposed to 1.5, 2, 2.5, 3, 3.5, or 4g for 5-7 hrs. The exposure to reduced temperature (Ta = approximately 7 degrees C) for 1 hr began 3 hrs after initiation of centrifugation. These experiments indicated that the magnitude of the cold-induced drop in Tco was linearly related to the acceleration field. The effect of a specific stressor (cold) on the thermoregulatory system is therefore a direct function of the gravitational field.

Acceleration↗
PubMed1978

The roles of body mass and gravity in determining the energy requirements of homoiotherms.

Studies by Kleiber and by Brody in the 1930's established the 3/4 power of body weight as the unit for comparison of metabolic phenomena in homoiotherms. Later Kleiber conceived of the energy requirement as a composite function, with a thermoregulatory component, proportional to heat loss, and an antigravity component that is directly proportional to body weight. Maintenance feed requirements have been measured with groups of small animals chronically exposed to several acceleration fields. Analysis of the results leads to an arithmetic relationship between the maintenance requirement and acceleration field strength: Fg = Fo+k g Where: F is the maintenance feed requirement (Fg in field of g strength, and Fo where g=0); and, g is the ambient acceleration field strength. When the equations are compared for groups of different body size, Fo tends to vary between the 0.4 and 0.5 power of body mass--and k tends to be the same, irrespective of body mass (BM). These findings tend to confirm the Kleiber concept of a composite nature of homoiotherm maintenance requirements.

Animals↗
PubMed1979

Gravity as a biochemical determinant.

The existence of obvious morphological and physiological changes in living systems exposed to altered gravity immediately informs us that prior changes have taken place in the chemistry of exposed cells, tissues and organs. These changes include transients that return more or less promptly to the norm when the system is restored to the terrestrial g-field. For example, altered serum hormone and electrolyte levels in man, which appear to reflect successful adaptation to the conditions of orbital weightlessness, disappear shortly after return to Earth. Other changes--in mineral and protein constituents of the skeletal system in man, and cell wall composition in plants--are more persistent or even permanent. Hypogravitational departures from the norm include not only "weightlessness" as achieved in orbit, but also experimental modes of compensation, on the clinostat or by flotation. These techniques are useful in the study of hypogravity but cannot replace fully the weightless environment. Plant ethylene and peroxidase both increase under orbital, clinostat and/or flotation conditions whereas 3-phosphoglyceraldehyde-dehydrogenase increases under orbital but not clinostat conditions; cytochrome reductase and malic dehydrogenase levels are affected by the clinostat, but not by actual weightless conditions. How do the altered organismal biochemistries induced by the centrifuge and the clinostat relate to one another? Does gravity operate on living systems as a continuous variable from 0 to superterrestrial values, or do deviations from g(earth) generate non-uniform, discontinuous stress responses, irrespective of sign? In plants, measurements of wall lignin content and peroxidase activity yield opposite answers. Given the limited data so far available we will consider the meaning of these contradictions.

Adaptation, Physiological↗
PubMed1979

Physiological effect of high, sustained +Gz forces on man.

Two studies were conducted to evaluate physiological responses and possible tolerance to high sustained +Gz forces at the USAF School of Aerospace Medicine, using the 20-ft (6.10 m) radius Human Centrifuge. In the first study (A), 14 human volunteer subjects--fully protected with an anti-G suit and performing the M-1 or L-1 straining maneuver--were exposed to +Gz forces. These forces began at +6.5 Gz, and increased weekly in 0.5 G increments to +9.0 Gz, for a duration of 45 sec at each level. Physiological performance was based mostly on the subjects' ability to maintain clear vision during the 45 sec exposure. Of the 14 subjects, 9 were able to maintain vision and remain at the +9 Gz level for 45 sec. In the second study (B), 12 human volunteer subjects--also protected with anti-G suits and using the straining maneuvers--were exposed to levels of +1, 3, 6, and 8 Gz, for 60 sec at each level. Extensive physiologic parameters were recorded in order to detect objective criteria which could be used as determinants for a medical tolerance endpoint to the particular level of +Gz stress. In both studies, the reasons for stopping the runs at levels exceeding +7.5 Gz included: fatigue, cardiac arrhythmias, blackout, and one occurrence of ventricular tachycardia. Other physiological responses to the sustained +Gz stress (such as heart rate, arterial blood pressure, central venous blood pressure, arterial oxygen saturation, gastric pressure, and ankle venous pressure) did not furnish specific information that could be used as "physiological tolerance limit" criteria.

Acceleration↗
PubMed1979

Prophylactic [correction of prophylatic] effects of intermittent acceleration against physiological deconditioning in simulated weightlessness.

The prophylactic effect on adult human males of intermittent acceleration against physiological deconditioning in weightlessness simulated by water immersion was studied at +0.8, +1.2, and +1.6 g. These prophylactic exposures reduced renal excretion of fluid and plasma volume changes, and increased venous compliance and the time at which the subjects could tolerate an acceleration field of +3 g.

Acceleration↗
PubMed1979

Effect of gravity on lymphocyte proliferation.

Reports on postflight examination of lymphocytes from crew members of soviet and american spaceships show a depression of reactivity towards mitogens in vitro. The purpose of this communication is to present experimental evidence that gravity can interfere with lymphocyte activation. Lymphocytes were incubated in the presence of concanavalin A in a centrifuge at 2 and 4 g for four days. This environment causes a significant acceleration of the response to the mitogen. In addition, remarkable differences in the ultrastructure of cells grown at 1 g and 4 g are observed by electron microscopy. This investigation is related to the experiment "Effect of weightlessness on lymphocyte proliferation" experiment which will be performed during the first Spacelab mission.

Animals↗
PubMed1979

Rat growth during chronic centrifugation.

Female weanling rats were chronically centrifuged at 4.15 g with controls at terrestrial gravity. Samples of 6 to 10 rats were sacrificed for body composition studies at 0, 28, 63, 105, 179 and 308 days of centrifugation and 57 days after centrifugation ended. The centrifuged group had a significantly lower mature body mass than the controls (251 vs 318 g) but the rate of approach to the mature values was the same in both groups. Retirement to 1 g on the 60th day resulted in complete recovery. Masses of muscle, bone, skin, CNS, heart, kidneys, body water and body fat were changed in the centrifuged group. However, an analysis of the growth in mass of individual components relative to growth of the total fat-free compartment revealed that only skin (which increased in mass) was responding to centrifugation per se.

Adipose Tissue↗
PubMed1979

Influence of the ambient acceleration field upon acute acceleration tolerance in chickens.

It has been demonstrated both in the Russian and in the American space programs that there is a progressive deconditioning of the circulatory system with exposure to weightlessness. Astronauts and cosmonauts returned to Earth have a significantly reduced orthostatic tolerance which will persist for a few days. We have measured the acceleration tolerance of domestic fowl, acutely exposed to a 6 g+z field, as the time over which a normal heart rate can be maintained. This period of circulatory accommodation ends abruptly with a marked bradycardia, which with continued treatment is terminal. For animals which have been previously chronically accelerated (e.g., physiologically adapted to a 2.5 g field) the acute acceleration tolerance is greatly increased. It appears that the influence of the ambient acceleration field in conditioning the responsiveness of the circulatory system is a general phenomenon.

Acceleration↗
PubMedDate not supplied

Effectiveness of centrifuge-induced artificial gravity with ergometric exercise as a countermeasure during simulated microgravity exposure in humans.

To test the effectiveness of centrifuge-induced artificial gravity with ergometric exercise, 12 healthy young men (20.7 +/- 1.9 yr) were exposed to simulated microgravity for 14 days of -6 degrees head-down bedrest. Half the subjects were randomly selected and loaded 1.2 G artificial gravity with 60 W (four out of six subjects) or 40 W (two out of six subjects) of ergometric workload on days 1, 2, 3, 5, 7, 9, 11, 12, 13, 14 (CM group). The rest of the subjects served as the control. Anti-G score, defined as the G-load x running time to the endpoint, was significantly elongated by the load of the centrifuge-ergometer. Plasma volume loss was suppressed (-5.0 +/- 2.4 vs. -16.4 +/- 1.9%), and fluid volume shift was prevented by the countermeasure load. Elevated heart rate and muscle sympathetic nerve activity after bedrest were counteracted, and exaggerated response to head-up tilt was also suppressed. Centrifuge-induced artificial gravity with exercise is effective in preventing cardiovascular deconditioning due to microgravity exposure, however, an effective and appropriate regimen (magnitude of G-load and exercise workload) should be determined in future studies.

Adult↗
PubMed2005

Graviperception in ciliates: steps in the transduction chain.

Ciliates represent suitable model systems to study the mechanisms of graviperception and signal transduction as they show clear gravity-induced behavioural responses (gravitaxis and gravikinesis). The cytoplasm seems to act as a "statolith" stimulating mechanosensitive ion channels in the cell membrane. In order to test this hypothesis, electrophysiological studies with Stylonychia mytilus were performed, revealing the proposed changes (de- or hyperpolarization) depending on the cell's spatial orientation. The behaviour of Paramecium and Stylonychia was also analyzed during variable acceleration conditions of parabolic flights (5th German Parabolic Flight Campaign, 2003). The corresponding data confirm the relaxation of the graviresponses in microgravity as well as the existence of thresholds of graviresponses, which are found to be in the range of 0.4xg (gravikinesis) and 0.6xg (gravitaxis).

Animals↗
PubMed2004

Feasibility of preparing nanodrugs by high-gravity reactive precipitation.

To study the feasibility of producing nanoparticles of organic pharmaceuticals using a novel high-gravity reactive precipitation (HGRP) technique, reactive precipitation of benzoic acid as a model compound was carried out in a rotating packed bed under high gravity. The main factors such as the rotating bed speed, concentration and volume flow rate of the reactants (sodium benzoate and HCl) affecting the particle size of the precipitate were studied. Particle size was measured by transmission electron microscopy. Benzoic acid was precipitated as nanoparticles as fine as 10nm. The particle size was decreased with increasing rotating bed speed, concentration and volume flow rate of the reactants. The formation of ultrafine particles was due to intensified micro-mixing of reactants in the rotating bed to enhance nucleation while suppressing crystal growth. The results have demonstrated the feasibility to produce nanodrugs by the principle of acid-base precipitating reaction using HGRP.

Benzoic Acid↗
PubMed2006

Production of salbutamol sulfate for inhalation by high-gravity controlled antisolvent precipitation.

The purpose of this study was to produce salbutamol sulfate (SS) as a model anti-asthmatic drug using high-gravity controlled precipitation (HGCP) through antisolvent crystallisation. An aqueous solution of SS was passed through a HGCP reactor with isopropanol as antisolvent to induce precipitation. Spray drying was employed to obtain dry powders. Scanning electron microscopy, X-ray powder diffraction (XRD), density measurement, thermal gravimetric analysis, and dynamic vapour sorption were carried out to characterise the powder physical properties. The aerosol performance of the powders was measured using an Aeroliser connected to a multiple stage liquid impinger operating at 60 L/min. The HGCP SS particles were elongated with 0.1 microm in width but varying length of several mum, which formed spherical agglomerates when spray dried. The particles showed the same XRD pattern and true density (1.3g/cm3) as the raw material, indicating that they belonged to the same crystalline form. However, the spray dried agglomerates had a much lower tapped density (0.1g/cm3) than the raw material (0.6g/cm3). Compared with the powder obtained by spray drying directly from an aqueous solution, the SS powders obtained from HGCP were much less hygroscopic (0.6% versus 10% water uptake at 90% RH). The in vitro aerosol performance showed a fine particle fraction FPFloaded and FPFemitted up to 54.5+/-4.9% and 71.3+/-10.0%, respectively. In conclusion, SS powder with suitable physical and aerosol properties can be obtained through antisolvent HGCP followed by spray drying.

Aerosols↗