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PubMed2000

Aerobic exercise as a countermeasure for microgravity-induced bone loss and muscle atrophy in a rat hindlimb suspension model.

BACKGROUND: Loss of bone and skeletal muscle atrophy resulting from non-weight-bearing are major concerns associated with microgravity environment and spaceflight deconditioning. The objective of this research was to address the fundamental issue of whether bone loss and muscle atrophy could be attenuated using weight-bearing aerobic exercise on a treadmill as a countermeasure in rats subjected to simulated weightlessness by hindlimb suspension. METHOD: Bone and muscle from control and hindlimb-suspended groups with and without exercise were evaluated by bone mineral density (BMD), mechanical tests, bone histomorphometry and muscle mass. RESULTS: Femoral BMD of hindlimb-suspended (HS) rats subjected to treadmill exercise was significantly greater than femoral BMD of HS rats without exercise and also was equivalent to that of weight-bearing controls. Muscle mass from HS rats exercised on a treadmill was significantly greater than muscle mass from HS rats that did not exercise. Exercise did not result in muscle mass equal to that of controls, however. In addition, histomorphometric analysis of the metaphysis of the proximal tibia revealed that HS rats that exercised did not maintain bone formation equivalent to controls. No other bone parameters were found to vary significantly between groups. CONCLUSIONS: It was concluded that moderate aerobic exercise on a treadmill did attenuate bone loss and muscle atrophy due to simulated weightlessness by hindlimb suspension, however its effectiveness differed by tissue, anatomical site and parameter investigated.

Animals↗
PubMed2000

Medical imaging in microgravity.

Microgravity environment induces significant pathophysiological changes in humans. As long-term space habitation and interplanetary missions become commonplace in the next century, researchers and imaging specialists must embrace the unique challenges of microgravity research in developing innovative uses of imaging technology. Microgravity results in cephalad fluid shift, loss of electrolytes, loss of muscle and bone mass, anemia, reduced immune response, variability in gastric emptying and hepatic metabolism, increased bowel transit, and development of space motion sickness. Medical imaging is uniquely capable of assessing all of these physiologic adaptations to weightlessness. The imaging information will also aid in identifying those changes which are potentially beneficial and those which are harmful to humans living in space. Interventions may then be employed to capitalize on the benefits and prevent the harmful effects. This article reviews the physiological adaptations to weightlessness and outlines ways in which medical imaging techniques may provide insight into these adaptations.

Adaptation, Physiological↗
PubMed1993

Effect of short- and long-term spaceflight on the contractile properties of rat skeletal muscles with different functions.

In the Cosmos biosputnik 1514, 1667, 1887, 2044 and 1129 the rats 5, 7, 12,5, 15, 18,5 days were in weightlessness state. Due to the adaptation of the skeletal muscles' weightlessness the adaptation was different in various muscles, which depends on the time of participation in antigravitation, the composition of the fibers and from the biometrical characteristics. In different muscles, the changing of the metabolism and the structure of the muscles more than likely in connection with the changing of the myosin subordinate unit compositions. In our experiments we had studied, as to how the muscular atrophy changes, does it increase all the time, or does it balances out after reaching a certain stage.

Adaptation, Physiological↗
PubMed1995

Changes in blood biochemical parameters in tail-suspended rats.

There have been many studies on the effects of gravity on animals and humans. In particular, weightlessness and the time course of physiological shifts in space acclimation are the most significant problems in a space environment. In a laboratory setting, tail suspension in rats has been utilized for simulation of weightlessness. We therefore utilized this technique in order to study the influence of microgravity on blood constituents in rats. It was clarified that some blood biochemical parameters were effected for the duration of suspension exposure, and they are reported here.

Animals↗
PubMed1995

Sleep-wake cycles in rhesus monkeys during Spacelab flight simulations.

Neurophysiological data has been obtained in orbital flight from various non-human Primates. Aboard Russian satellites during both Bion and Biocosmos missions, impairments in duration and organization of the states of vigilance were observed in rhesus monkeys during flight: increase in nocturnal awakening, decrease of Rapid Eye Movements-sleep (REM-sleep). It was assumed that weightlessness played a role in these changes. The former "Rhesus Project", a joint program between CNES and NASA, was devoted to physiological studies using the rhesus monkey as a human model aboard Spacelab, during 14 to 16 day orbital flights. In the first stage of this project, we investigated the effect of experimental conditions as well as specific restraint and confinement on the circadian sleep-wake rhythm in a group of rhesus monkeys. Prior to flight, our aim was to determine quantitatively and qualitatively sleep-wake cycles. These control data would thus be compared with inflight data in order to assess the influence of weightlessness.

Activity Cycles↗
PubMed1996

[Cerebral cortical blood flow during parabolic maneuvers].

Cerebral cortical blood flow (CBF) was measured in 6 rabbits during parabolic flight maneuvers (20 s of weightlessness). During the first seconds of weightlessness, CBF increased up to 100% when compared with CBF at 1 G. Since this transient increase (5 s) was not modified when propranolol or pentobarbital was given to the animals, one can hypothesize that it was not related to stress.

Animals↗
PubMed1991

Tropistic responses of Avena seedlings in simulated hypogravity.

Results from investigation of the gravitropic responses of the Avena coleoptile under simulated weightlessness are presented. The tests were conducted using the flight hardware, identified by NASA as the Gravitational Plant Physiology Facility (GPPF), designed to support the Spacelab experiment, GTHRES. Weightlessness or so-called microgravity-conditions were simulated by the use of a so-called somersault clinostat. The plants were gravitropically stimulated with different g-forces and stimulation durations on a centrifuge. Timelapse video pictures of the plants were taken during the last hour prior to the stimulation and in a period of 3 hours after. The gravitropic responses of the plants were analyzed with the aid of an image analyzing system. Dose-response curves for stimulation forces 0.2, 0.4, 0.6, 0.8, and 1.0 g with different stimulation times ranging from 2 to 250 min were achieved. The results show that the reciprocity between force and stimulation time may be valid for small stimulation doses (lower than 5 g min), but not for larger doses. Furthermore, the threshold values (i.e. the smallest stimulation the plants are able to detect) found by extrapolation of the dose response curves, are less than 30 g s. The results are discussed with respect to an accepted space experiment, GTHRES, where the corresponding experiments will be carried out in the same apparatus under true microgravity conditions.

Avena↗
PubMed1995

Gravitropic responses of the Avena coleoptile in space and on clinostats. I. Gravitropic response thresholds.

We conducted a series of gravitropic experiments on Avena coleoptiles in the weightlessness environment of Spacelab. The purpose was to test the threshold stimulus, reciprocity rule and autotropic reactions to a range of g-force stimulations of different intensities and durations The tests avoided the potentially complicating effects of earth's gravity and the interference from clinostat ambiguities. Using slow-speed centrifuges, coleoptiles received transversal accelerations in the hypogravity range between 0.l and 1.0 g over periods that ranged from 2 to 130 min. All responses that occurred in weightlessness were compared to clinostat experiments on earth using the same apparatus. Characteristic gravitropistic response patterns of Atuena were not substantially different from those observed in ground-based experiments. Gravitropic presentation times were extrapolated. The threshold at 1.0 g was less than 1 min (shortest stimulation time 2 min), in agreement with values obtained on the ground. The least stimulus tested, 0.1 g for 130 min, produced a significant response. Therefore the absolute threshold for a gravitropic response is less than 0.1 g.

Acceleration↗
PubMed1997

[The effects of space condition on the germination of medicinal plant Carthamus tinctorius].

OBJECTIVE: To substantiate the effects of space condition on the growth and development of medicinal plants. METHODS: The seeds of Carthamus tinctorius L. were set up in retrievable satellites. After returning earth, the germination of these seeds were observed by electrophoresis. The isozymes of peroxidases, esterase and soluble proteins were also evaluated. RESULTS: The average seed germinative rate of the space flight group was higher than that of the earth controlled group, and the peroxidase activity of the space flight group was higher than that of the earth controlled group either. The electrophoresis patterns of isozymes and proteins between the space flight group and the earth controlled group showed only little difference in bud bursting stage. CONCLUSION: Weightlessness and radiation in space affect the germination of Carthamus tinctorius, and they show little effect on gene expression in the stage of germination. Weightlessness may be the important factor to improve the peroxidase activity.

Cosmic Radiation↗
PubMed1997

[Changes in morphology and calcium content of otoconia in rats after 120 d tail-suspension].

The morphology and calcium content of otoconia in rats after long term (120 d) tail-suspension were studied using scanning electron microscopy (SEM) and X-ray microanalysis, respectively. The results showed that after 120 d simulated weightlessness otoconia were round, irregularly shaped, or with fissures, and there were rough and fine granular or small globular substances on the surface. X-ray microanalysis showed that the calcium content in the otoconia of both utricule and saccule was significantly decreased in the 120 d tail-suspended rats than that in control (P < 0.01). These results suggest that a long term(120 d) simulation of the headward distribution of blood volume and hindlimb underloading effect induced by weightlessness may cause the morphological changes and lower calcium content of the otoconia. Finally, the possible mechanism and the physiologic meaning of these findings are discussed.

Animals↗
PubMed1999

Nutritional biochemistry of space flight.

Humans have flown in space for more than 35 years. Since that time, Americans have walked on the moon, launched two space stations (Skylab and the International Space Station), docked during orbit with a Soviet Soyuz space capsule and the Russian Mir space station, flown the only reusable space vehicle, and visited a Russian space station for more then 6 months at a time. Nutritional intake has not been considered a high priority during relatively brief flights of the Space Shuttle and other programs (i.e., less than 21 days). However, as we embark on extended-duration (i.e., > 30 days up to several years) missions, nutrition becomes a critical issue. The impact of weightlessness on human physiology is profound. We are in the very early stages of understanding how space flight affects nutrient requirements and related issues such as absorption, metabolism, and excretion. Apart from the obvious role of providing energy and required nutrients, nutrition is also important in terms of enhancing psychosocial interactions among crews, and ameliorating some of the effects of microgravity on the body (i.e., acting as a "countermeasure"). The interrelationships among space flight, nutrition, and physiology suggest that a program of specified nutritional intake may be required to enhance mission safety and crew productivity. Defining which nutrients are essential for the space flight environment depends on a more complete understanding of how weightlessness affects physiology. Providing the required nutrients is also limited by the types of foods that can be provided by the food system on board the space craft, and the dietary habits of space crews.

Adaptation, Physiological↗
PubMed1993

Fungi in space--literature survey on fungi used for space research.

A complete review of the scientific literature on experiments involving fungi in space is presented. This review begins with balloon experiments around 1935 which carried fungal spores, rocket experiments in the 1950's and 60's, satellite and moon expeditions, long-time orbit experiments and Spacelab missions in the 1980's and 90's. All these missions were aimed at examining the influence of cosmic radiation and weightlessness on genetic, physiological, and morphogenetic processes. During the 2nd German Spacelab mission (D-2, April/May 1993), the experiment FUNGI provided the facilities to cultivate higher basidiomycetes over a period of 10 d in orbit, document gravimorphogenesis and chemically fix fruiting bodies under weightlessness for subsequent ultrastructural analysis. This review shows the necessity of space travel for research on the graviperception of higher fungi and demonstrates the novelty of the experiment FUNGI performed within the framework of the D-2 mission.

Cosmic Radiation↗
PubMed1998

Microvibrations: an interrelation between heart beat, muscle tremor and resting muscle tone.

The phenomenon of microvibrations was described by Rohracher in Vienna in the 1950s. Microvibrations consist of oscillationns in the frequency range of 7 to 13 Hz which can be observed on the surface of the body during a complete muscle relaxation. We had the opportunity to study the changes of microvibrations and physiological tremor under the condition of weightlessness in the Russian Space Station MIR during the so called "Austromir" project and the following Russian long term flights including the record flight of cosmonaut Polyakow. The recordings have been made by accelerometers from the body surface. It was found that during wieghtlessness the typical 7 to 13 Hz oscillations disappeared as well from microvibrations as from physiological tremor. By the application of a simple model it can be shown that microvibrations are due to mechanical resonance. The oscillations are apparently elicited by the heart beat. Therefore it appears that microvibrations are cardioballistic phenomena. It can be shown that cardioballistic forces are transmitted by osseous structures to soft tissues like e.g. relaxed muscles. Local resonance finally leads to the oscillations as mentioned above. From the model calculations we conclude that the relaxation is much more pronounced during weightlessness. Thus, resonance is abolished in the frequency region mentioned above. On the ground even during muscle relaxation there is still some muscle tone with an elastic component which under this condition permits the generation of resonance phenomena. Our results permit a new interpretation of microvibrations. Furthermore, the results may have importance for the interpretation of the generation of certain pathological forms of tremor.

Adult↗
PubMed1998

Muscle sympathetic nerve activity and plasma norepinephrine during 6 degrees head-down bed rest.

Alterations in autonomic function are evident during spaceflight. These conditions are also simulated by ground-based experimental models of a microgravity environment such as 6 degrees head-down bed rest (BR). They include a reduction in baroreflex function, a decrease in vagal tone and a loss of circulatory blood volume during weightlessness. However, it is not clear whether vasomotor sympathetic outflow, which controls peripheral vascular tone neurally, and plasma norepinephrine concentration will change or not during weightlessness. The purpose of the present study is to examine changes in vasomotor sympathetic nerve activity during six days of 6 degrees head-down BR. Vasomotor sympathetic nervous activity was evaluated by the direct recording of muscle sympathetic nerve activity (MSNA) by a use of microneurographic technique. MSNA on the sixth day during BR was the same as that in a horizontally supine position before BR (before BR; 15.4 +/- 1.6 bursts/min, during BR; 16.7 +/- 3.5 bursts/min), though plasma norepinephrine concentrations during BR were reduced by 25% compared with those before BR (before BR; 263 +/- 33 pg/ml, during BR; 193 +/- 79 pg/ml, p < 0.05). This dissociation cannot be determined precisely, but it suggests the possibility of peripheral changes in terminal sympathetic nerve endings, etc.

Adult↗
PubMed1999

[Changes of blood circulation, muscle and skeletal systems in 30 d tail-suspended [correction of tail-suspented] rats].

OBJECTIVE: To confirm the tail-suspended rat model for the study of countermeasures against weightlessness. METHOD: The changes of blood circulation, muscle and skeletal systems in control group rats (n = 15) and 30 d tail-suspended rats (n = 15) were compared. RESULT: Compared with the control group, the hemorrheology and erythrocyte deformability decreased significantly, muscle-fiber atrophy, muscle contraction function decreased, the type I muscle fibers transformed to the type II muscle fibers, bone-mineral content of L3 and load capacity of femur declined, bone metabolism changed in the suspended rats. CONCLUSION: The tail-suspended rat is a suitable animal model for the study of countermeasures against weightlessness.

Animals↗
PubMed1998

[Effect of space environment on germination and vegetation growth in Carthamus tinctorius L].

OBJECTIVE: To substantiate the effects of space condition on medicinal plants. METHOD: The seeds of medicinal plant Carthamus tinctorius were carried on board a retrievable satellite during 3-18 July, 1994. After returing to earth, the seedling rate, state of growth and development were observed. RESULT: The seeding rates, plant heights and branch quantities of weightless seeds and the seeds which were penetrated once and less than once by the heavy ion rays were higher than those of the seeds which were kept on earth, but these indexes of the seeds which were penetrated 2-3 times by the heavy ion rays were higher than those of the ground controlled seeds. CONCLUSION: Weightlessness and little penetration promote the growth and development of Carthamus tinctorius, but much penetration functions the other way round.

Carthamus tinctorius↗
PubMed1999

[The effects of space flight on medicinal plant Datura innoxia].

OBJECTIVE: To probe the effects of space condition on medicinal plants. METHODS: The seeds of Datura innoxia Mill were put in a retrievable satellite. After returning earth, the isozymes of peroxidases, esterase and soluble proteins were studied. RESULTS: The peroxidase activity and the protein content of weightless group were lower than that of the earth controlled group, but these items of the hit group were higher than that of the earth controlled group. The electrophoresis patterns of isozymes and proteins of these three groups were similar. CONCLUSION: The effects of weightlessness and the high energy heavy ions were different on Datura innoxia, and the effects of space conditions were not enough to produce idiovariation in Datura innoxia.

Cosmic Radiation↗
PubMed2000

[Effects of -30 degrees head down tilt on lung function].

OBJECTIVE: To investigate the effects of short-term simulated weightlessness on lung function in healthy males. METHOD: -30 degrees head down tilt for 45 min was used to simulate short-period weightlessness. Lung function of 12 healthy males, aged 18-21, were studied with plethysmography during seating, supine and head down tilt positions. At the same time, blood flow in pulmonary artery and function of right ventricle were measured with Doppler Echo-Cardiography. Comparative analysis was done. RESULT: As body position changed from seating or supine into head down tilt, FVC, FEV1, FEV1%, MVV, VA and IVC decreased. The change of MVV was the most prominent (P < 0.000). As the position changed, pulmonary diffusion increased dramatically (DL(CO) P<0.001, K(CO) P<0.000). CONCLUSION: HDT may lead to a decrease of pulmonary ventilation and lung capacity. The increased pulmonary diffusion might be related to uniform distribution of pulmonary blood flow and increased effective pulmonary vascular bed.

Adolescent↗