Morpho-functional alterations in testicular and nervous cells submitted to modelled microgravity

Humans, as well as other life forms, have developed on earth under the terrestrial gravitational field. Questions concerning the effect of the gravity vector changes on the animal physiology have begun to emerge only in the last decades. Physiological alterations were observed during space flights, but space-born investigations at cellular levels are still very limited. Earth-bound simulations of low gravity obtained with the 3-dimensional Random Positioning Machine are extensively utilized to explore the effects of microgravity on cell function. After only a few minutes, weightlessness affected the cytoskeleton of lymphocytes, astrocytes, neurons and testicular cells, disorganizing microtubules, intermediate filaments and microfilaments. Cell division was impaired, mitochondria were disrupted and apoptotic phenomena occurred. Expression of proteins involved in transmembrane ion and water transport were also affected. In the Leydig cells the key enzymes (3beta- and 17beta-hydroxysteroid dehydrogenases) leading to testosterone synthesis were depressed. However, after 20 h of clinorotation the cells were able to synthesize heat shock proteins that initiated protection and recovery. The cytoskeleton was again well organized, normal mitosis occurred and the percentage of apoptotic cells returned to the range of 5%, similar to the control cultures. Ion and water transmembrane proteins and steroid dehydrogenases returned to normal levels. Long-term experiments showed that low gravity induced only transient alterations in the cultured cells, which were able to adapt to the gravity vector changes and to regain normal activity. These data may explain the physiological adaptation occurring in astronauts during and after space flights.

Effects of space flight conditions on the function of the immune system and catecholamine production simulated in a rodent model of hindlimb unloading

The rodent model of hindlimb unloading has been successfully used to simulate some of the effects of space flight conditions. Previous studies have indicated that mice exposed to hindlimb-unloading conditions have decreased resistance to infections compared to restrained and normally housed control mice.

OBJECTIVE

The purpose of this study was to clarify the mechanisms involved in resistance to infection in this model by examining the effects of hindlimb unloading on the function of the immune system and its impact on the production of catecholamines.

METHODS

Female Swiss Webster mice were hindlimb-unloaded during 48 h and the function of the immune system was assessed in spleen and peritoneal cells immediately after this period. In addition, the kinetics of catecholamine production was measured throughout the hindlimb-unloading period.

RESULTS

The function of the immune system was significantly suppressed in the hindlimb-unloaded group compared to restrained and normally housed control mice. Levels of catecholamines were increased in the hindlimb-unloaded group and peaked at 12 h following the commencement of unloading.

CONCLUSION

These results suggest that physiological responses of mice are altered early after hindlimb unloading and that catecholamines may play a critical role in the modulation of the immune system. These changes may affect the ability of mice to resist infections.

The implementation of game in a 20-day head-down tilting bed rest experiment upon mood status and neurotic levels of rest subjects

This study evaluated the effect of the implementation of game on mental health among participants in a bedrest (BR) experiment. Subjects were 12 healthy males aged 20-26, who participated in a 20-day 6-degrees head-down tilting BR experiment. The participants were asked to complete psychometrical questionnaires before, during, and after the experiment. We entrusted the participants to manage their leisure time and they intended a game in which all of them could take part over the experiment period. The general conversation and light-hearted mood among the subjects continued during the experimental period. Longitudinal data analysis showed that levels of neurosis and mood status did not deteriorate during the experiment, while our previous experiments, which were performed under the same protocol as this study except for the implementation of the game showed a distinct deterioration in psychosocial status. We consider that the implementation of game autonomously contributes to the positive effects on the mental health among the participants.

Responses of neuromuscular systems under gravity or microgravity environment

Hindlimb suspension of rats induces induces fiber atrophy and type shift of muscle fibers. In contrast, there is no change in the cell size or oxidative enzyme activity of spinal motoneurons innervating muscle fibers. Growth-related increases in the cell size of muscle fibers and their spinal motoneurons are inhibited by hindlimb suspension. Exposure to microgravity induces atrophy of fibers (especially slow-twitch fibers) and shift of fibers from slow- to fast-twitch type in skeletal muscles (especially slow, anti-gravity muscles). In addition, a decrease in the oxidative enzyme activity of spinal motoneurons innervating slow-twitch fibers and of sensory neurons in the dorsal root ganglion is observed following exposure to microgravity. It is concluded that neuromuscular activities are important for maintaining metabolism and function of neuromuscular systems at an early postnatal development and that gravity effects both efferent and afferent neural pathways.

Plasma volume restoration with salt tablets and water after bed rest prevents orthostatic hypotension and changes in supine hemodynamic and endocrine variables

Head-down bed rest changes the values of many cardiovascular and endocrine variables and also elicits significant hypovolemia. Because previous studies had not controlled for hypovolemia, it is unknown whether the reported changes were primary effects of bed rest or secondary effects of bed rest-induced hypovolemia. We hypothesized that restoring plasma volume with salt tablets and water after 12 days of head-down bed rest would result in an absence of hemodynamic and endocrine changes and a reduced incidence of orthostatic hypotension. In 10 men, we measured changes from pre-bed-rest to post-bed-rest in venous and arterial pressures; heart rate; stroke volume; cardiac output; vascular resistance; plasma norepinephrine, epinephrine, vasopressin, renin activity (PRA), and aldosterone responses to different tilt levels (0 degrees, -10 degrees, 20 degrees, 30 degrees, and 70 degrees); and plasma volume and platelet alpha2- and lymphocyte beta2-adrenoreceptor densities and affinities (0 degrees tilt only). Fluid loading at the end of bed rest restored plasma volume and resulted in the absence of post-bed-rest orthostatic hypotension and changes in supine hemodynamic and endocrine variables. Fluid loading did not prevent post-bed-rest increases in beta2-adrenoreceptor density or decreases in the aldosterone-to-PRA ratio (P = 0.05 for each). Heart rate, epinephrine, and PRA responses to upright tilt after bed rest were increased (P < 0.05), despite the fluid load. These results suggest that incidents of orthostatic hypotension and many of the changes in supine hemodynamic and endocrine variables in volume-depleted bed-rested subjects occur secondarily to the hypovolemia. Despite normovolemia after bed rest, beta2-adrenoreceptors were upregulated, and heart rate, epinephrine, and PRA responses to tilt were augmented, indicating that these changes are independent of volume depletion.

Active hexose correlated compound enhances the immune function of mice in the hindlimb-unloading model of spaceflight conditions

Hindlimb unloading is a ground-based model that simulates some of the aspects of spaceflight conditions, including lack of load bearing on hindlimbs and a fluid shift to the head. It has been shown that treatment with active hexose correlated compound (AHCC) restores resistance to infection in mice maintained under hindlimb-unloading conditions. The present study was designed to clarify the mechanisms by which AHCC enhances resistance to infection in this model. We hypothesized that oral administration of AHCC will enhance the function of the immune system, which could lead to the increased resistance to infection observed in this model. AHCC or the excipient was orally administered to mice, and the function of the immune system was assessed in spleen and peritoneal cells isolated from those groups. The results of the present study showed that administration of AHCC for 1 wk before and throughout the second day of the hindlimb-unloading period enhanced the function of the immune system assessed by spleen cell proliferation and cytokine production in spleens and nitric oxide and cytokine production in peritoneal cells. These findings suggest that AHCC can be used as a potent immunoenhancer, especially in cases in which the immune system is suppressed by any condition, including diseases such as human immunodeficiency virus infection and cancer.

Influence of simulated weightlessness on the pharmacokinetics of acetaminophen administered by the oral route: a study in the rat

During space flights, the human body is submitted to weightlessness which induces physiological variations that could modify drug disposition during space missions. Since space experiments are infrequent and difficult to perform, in order to evaluate pharmacokinetic modifications, simulation experiments of weightlessness have to be carried out on earth, using animal-models such as the Morey-Holton model. In this model, rats are suspended by the tail with their front paws on the ground. We studied the effects of simulated weightlessness on drug absorption and on gastric emptying, using acetaminophen as a probe. Three periods of suspension (1, 2 and 5 days) were compared with two control groups (free and attached rats). The attached group was used to evaluate a possible 'stress effect' caused by the suspension device. Each group was composed of 36 rats (12 sampling times and three rats per time). An oral dose of acetaminophen (100 mg/kg) was administered and blood samples were collected before and up to 12 h after administration. Plasma assays were performed using an high-performance liquid chromatography method with UV detection. The calculated population pharmacokinetic parameters were Ka, Kel (first order absorption and elimination constants) and Vd/F (apparent volume of distribution). The statistical interpretation of the population pharmacokinetic parameters indicated that 2 days of suspension significantly decreased the Vd/F by 83% and the Ka by 125%. The increase in the Ka was probably because of an increased acceleration of the gastric emptying and/or to a decrease in the total peripheral resistance which increased intestinal blood flow.

Daily short-period gravitation can prevent functional and structural changes in arteries of simulated microgravity rats

This study was designed to clarify whether simulated microgravity-induced differential adaptational changes in cerebral and hindlimb arteries could be prevented by daily short-period restoration of the normal distribution of transmural pressure across arterial vasculature by either dorsoventral or footward gravitational loading. Tail suspension (Sus) for 28 days was used to simulate cardiovascular deconditioning due to microgravity. Daily standing (STD) for 1, 2, or 4 h, or +45° head-up tilt (HUT) for 2 or 4 h was used to provide short-period dorsoventral or footward gravitational loading as countermeasure. Functional studies showed that Sus alone induced an enhancement and depression in vasoconstrictor responsiveness of basilar and femoral arterial rings, respectively, as previously reported. These differential functional alterations can be prevented by either of the two kinds of daily gravitational loading treatments. Surprisingly, daily STD for as short as 1 h was sufficient to prevent the differential functional changes that might occur due to Sus alone. In morphological studies, the effectiveness of daily 4-h HUT or 1-h STD in preventing the differential remodeling changes in the structure of basilar and anterior tibial arteries induced by Sus alone was examined by histomorphometry. The results showed that both the hypertrophic and atrophic changes that might occur, respectively, in cerebral and hindlimb arteries due to Sus alone were prevented not only by daily HUT for 4 h but also by daily STD even for 1 h. These data indicate that daily gravitational loading by STD for as short as 1 h is sufficient to prevent differential adaptational changes in function and structure of vessels in different anatomic regions induced by a medium-term simulated microgravity.

[Male fertility in space]

The effects of simulated microgravity on mammalian reproduction were studied using tail-suspended mice, during parabolic flight in a jet plane and in a horizontal clinostat device. In the tail-suspended mouse, which is a model of the shift of body fluid in a microgravity environment, atrophy of the testis and decrease of serum testosterone level were observed. The sperm motility decreased in the muG condition produced by the parabolic flight. There were no statistically significant differences in the efficiency of achieving normal fertilization in vitro, but there was a statistically significant decrease in the number of embryos reaching the morula and blastocyst stages after 96 hours in culture under clinostat rotation. These results suggest that the process of fertilization in vitro is not sensitive to the gravitational vector. However, the possibility exists that microgravity increases the disturbance of spermatogenesis and sperm motility or the frequency of early embryonic lethality. On the possibility of reproduction in space, there are some problems such as the cosmic radiation besides gravity. It is necessary to carry out further experiments in outer space.

Enhanced insulin action on glucose transport and insulin signaling in 7-day unweighted rat soleus muscle

Hindlimb suspension (HS), a model of simulated weightlessness, enhances insulin action on glucose transport in unweighted rat soleus muscle. In the present study, we tested the hypothesis that these changes in glucose transport in 3- and 7-day HS soleus of juvenile, female Sprague-Dawley rats were due to increased functionality of insulin signaling factors, including insulin receptor (IR), IR substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3-kinase), and Akt. Insulin-stimulated (2 mU/ml) glucose transport was significantly ( P < 0.05) enhanced in 3- and 7-day HS soleus by 59 and 113%, respectively, compared with weight-bearing controls. Insulin-stimulated tyrosine phosphorylation of IR and Ser473phosphorylation of Akt was not altered by unweighting. Despite decreased (34 and 64%) IRS-1 protein in 3- and 7-day HS soleus, absolute insulin-stimulated tyrosine phosphorylation of IRS-1 was not diminished, indicating relative increases in IRS-1 phosphorylation of 62 and 184%, respectively. In the 7-day HS soleus, this was accompanied by increased (47%) insulin-stimulated IRS-1 associated with the p85 subunit of PI3-kinase. Interestingly, the enhanced insulin-stimulated glucose transport in the unweighted soleus was not completely inhibited (89–92%) by wortmannin, a PI3-kinase inhibitor. Finally, protein expression and activation of p38 MAPK, a stress-activated serine/threonine kinase associated with insulin resistance, was decreased by 32 and 18% in 7-day HS soleus. These results indicate that the increased insulin action on glucose transport in the 7-day unweighted soleus is associated with increased insulin signaling through IRS-1 and PI3-kinase and decreased p38 MAPK protein expression. However, PI3-kinase-independent mechanisms must also play a small role in this adaptive response to HS.

Brain vessels in the rats exposed to primary and repeated tail-suspension. Minimization of structural changes after repeated exposure

The aim of study was histological examination of brain vessels in the rats exposed to repeated tail-suspension (TS). The rats were subjected to 30-day TS, then readapted to horizontal position for 30 days and again exposed to 14-day TS simultaneously with the rats which were underwent to 14-day TS for the first time. 30-day TS induced in brain vessels the adaptive changes hindering the excessive blood inflow to brain--spasm and hypertrophy of muscle-elastic valves in extra- and intracerebral arteries and also the destructive changes--loss of vascular tone in extra- and intracerebral arteries, plethora in extra- and intracerebral veins, intracerebral venules and capillaries, conglutination of erythrocytes in capillaries, plasmatization of veins and capillaries and edema of brain tissue pointing out in total the increase in blood inflow to the brain and difficulty of blood outflow. After 30-day readaptation of TS-rats to horizontal position only adaptive changes in extracerebral arteries and intracerebral capillaries (cell proliferation) and edema of brain tissue were revealed. After repeated, 14-day TS in spite of new redistribution of blood to the head, in contrast to the vessel alterations after primary 14-day TS, the adaptive and destructive changes in brain vessels were lack, excluding only moderate plethora of intracerebral veins, cell proliferation in capillaries and weak signs of edema.

Interactions of cells in zones of bone resorption under microgravity and hypokinesia

With the use of the methods of electron microscopy and autoradiography employing 3H-glycine the study was made of some morpho-functional cells-cells interactions (osteoblasts, osteocytes, macrophages, fibroblasts) in zones of adaptive remodeling of bone structures of the metaepiphyseal femoral bones of white rats which were during 28 days under experimental hypokinesia conditions, as well as of rats, flown on SLS-2 during 2 weeks. It is established that in zones of an increase of mineral matrix resorption some osteoblasts and osteocytes undergo destruction; a part of osteoblasts remains intact. The osteoclasts don't take part in destruction of osteoblasts and osteocytes. The utilization of the osteogenic cells detritus is accomplished by macrophages, coming to these zones. The resorption loci are filled not with the differentiating osteoblastic cells, as it is the case in the norm, but with fibroblasts and the bundles of collagen fibrils (fibrotic tissue) which do not undergo mineralization. Such changes are considered as one of the mechanisms of bone tissue response to a reduction of the supporting load.

Centrifugation as a countermeasure during actual and simulated microgravity: a review

This paper summarizes what has been learned from studies of the effects of artificial gravity generated by centrifugation in actual and simulated weightless conditions. The experience of artificial gravity during actual space flight in animals and humans are discussed. Studies using intermittent centrifugation during bed rest and water immersion, as a way to maintain orthostatic tolerance and exercise capacity, are reviewed; their results indicate that intermittent centrifugation is a potential countermeasure for maintaining the integrity of these physiological functions in extended space missions. These results can help set guidelines for future experiments aimed at validating the regimes of centrifugation as a countermeasure for space missions. Current and future research projects using artificial gravity conditions in humans are discussed.

Spaceflight and hindlimb suspension disuse models in mice

Osteoporosis is a disease characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and increased susceptibility to fractures. The microgravity of space creates an extreme environment that provides a model for osteoporosis in humans. This greatly accelerated form of osteopenia results in a 0.5-2% loss of bone mass per month. Rat models for this osteoporosis have been examined on many occasions, but STS-108 was the first Space Shuttle flight to use mice. Data reported to date indicate that spaceflight experiments with mice hold promise in predicting some spaceflight effects on humans. Due to the cost and infrequency of flights, ground-based models have been developed to mimic the deleterious effects of the microgravity environment. Hindlimb suspension is one such localized model. This model removes gravitational loading from the hindlimbs by suspending the animal by its tail to a guy wire that runs lengthwise across the cage. Because mice had not flown before STS-108, a direct comparison of this model's ability to predict spaceflight results has not been examined. The objective of this research is to closely repeat the STS-108 profile, with hindlimb suspension replacing spaceflight. This includes examining the ability of the protein osteoprotegerin, an osteoclast-inhibiting therapeutic, to mitigate the deleterious effects of skeletal unloading. It is expected that the results will lead to better understanding of the mechanisms of mineralization and bone remodeling to aid in development of countermeasures to prevent spaceflight induced osteoporosis and aid the treatment of osteoporosis here on earth.

Modifications of immunological and neuro-endocrine parameters induced by antiorthostatic bed-rest in human healthy volunteers

AIM

Space flight has profound effects on immunological and neuroendocrine parameters. Microgravity plays a major role in the induction of these changes. The aim of the present study was the evaluation on ground of the effects induced by antigravitary posture on immune and neuroendocrine functions.

METHODS

Eight healthy male volunteers (mean age 24+/-1 years) were maintained in antigravitary posture (-10 degrees) for 72 hours. Four of them were also maintained in supine posture for 72 hours as controls. The following immunological and neuroendocrine parameters have been analysed: peripheral white blood cells count, CD11b integrin expression and H(2)O(2) production by neutrophils, lymphocyte and monocyte phenotype, intracytoplasmic cytokine (IFN-gamma, TNF-alpha and IL-4) pattern, lymphocyte proliferation to mitogens and antigens, cortisol, ACTH, catecholamines, GH, LH, prolactin and testosterone plasma levels.

RESULTS

In subjects maintained in antigravitary posture, norepinephrine, dopamine, cortisol, ACTH, GH and prolactin plasma levels increased whereas H(2)O(2) production by neutrophils, lymphocyte proliferation, NK cells number and intracytoplasmic IFN-g expression decreased. No significant modifications were observed in subjects maintained in supine posture.

CONCLUSION

The results of this study indicate that several neuroendocrine and immunological parameters are modulated by a prolonged antigravitary posture on ground and may negatively affect astronauts defenses against pathogens during space flights.

[Impact of simulated microgravity on the expression and distribution of cardiac gap junction protein CX43]

OBJECTIVE

To observe the expression and distribution changes of connexin 43 (CX) in rats' myocardium after simulated microgravity and explore the partial mechanism of arrhythmia.

METHOD

Male Wistar rats were randomly assigned to either tail-suspension group (SUS) or control group (CON). Immunohistochemistry and Western Blot were used to detect the expression and the distribution of CX43. Electromicroscope was used to observe the ultrastructural changes.

RESULT

In SUS group, the decrease of CX43 and the distribution disturbance were obvious (P<0.05), the proportion of the side-to-side gap junction increased (P<0.05), and space between some gap junctions disappeared.

CONCLUSION

The results show that CX43 decreased significantly and distributed irregularly after simulated microgravity. These can cause the changes of cardiac electric conduction velocity and direction. As a result, conduction block and reentry may occur. And these might be the partial mechanism of cardiac arrhythmia.

[Image analysis of cardiac muscle cytoskeleton under simulated microgravity based on gray-level co-occurrence matrix (GLCM)]

OBJECTIVE

To study morphological changes of the cytoskeleton-microtubule (MT) of the fetal rat cardiac myocytes under simulated microgravity, and to quantify its image by utilizing the gray level co-occurrence matrix (GLCM) parameters of the image.

METHOD

Cytoskeleton images, including cellular microphotographs taken under normal or microgravity (clinostat) conditions, were quantified by gray level co-occurrence matrix parameters, and the pharmacological counter effect of quercetin against the influences of microgravity was estimated with these parameters.

RESULT

The results showed that the texture of microtubules in the image became worse under simulated microgravity environment. It also showed that quercetin has certain counter effect against the influence of microgravity.

CONCLUSION

The microtubule of the cardiac myocytes cytoskeleton becomes diffused under microgravity, and the GLCM parameters can well describe these variation. Quercetin has certain counter-effect against the influence of microgravity.

Adaptability of Japanese quail chicks to conditions of simulated weightlessness

The objective of this study was to evaluate the adaptability of young Japanese quail chicks to the simulated weightlessness, represented by hypodynamy. Unsexed hatchlings were subjected to hypodynamy on either the first, second or third day of age and reared under these conditions to 21 days of age. During this period, the control quail chicks were housed in a floor box. The effect of hypodynamy on adaptability of chicks was significant (P < 0.001). Approximately 75% of all chicks exposed to hypodynamy were not able to adapt in three experimental groups, although significant differences in adaptability were not found between these groups. Those birds were considered as non-adapted (eliminated from experiment) that manifested hyperactivity, escape attempts, turning 180 degrees in the sling, soaking in the water from the drinker, as well as the total apathy, at least three times per day. This experiment confirmed that some quail chicks are capable of adapting to conditions simulating weightlessness to 21 days of age and that the first 2-weeks after hatching may be a critical period of quail sensitivity to hypodynamy. This finding raises a key issue relevant to rearing quails in simulated weightlessness until the age of sexual maturity.

Effect of antiorthostatic bed rest on the human body

Head-down (-4 degrees) bedrest brings about a more rapid development of changes in haemodynamics, fluid displacement and nervous tone than traditional recumbent bed rest. Changes occurring during head-down hypokinesia have much in common with the changes typical of real weightlessness. They are characterized by phasic changes in the vascular tone. Under these conditions changes in the tone and blood-filling of the brain are important for the functional state of the vestibular apparatus.

Loss of T cell precursors after spaceflight and exposure to vector-averaged gravity

Using fetal thymus organ culture (FTOC), we examined the effects of spaceflight and vector-averaged gravity on T cell development. Under both conditions, the development of T cells was significantly attenuated. Exposure to spaceflight for 16 days resulted in a loss of precursors for CD4+, CD8+, and CD4+CD8+ T cells in a rat/mouse xenogeneic co-culture. A significant decrease in the same precursor cells, as well as a decrease in CD4-CD8- T cell precursors, was also observed in a murine C57BL/6 FTOC after rotation in a clinostat to produce a vector-averaged microgravity-like environment. The block in T cell development appeared to occur between the pre-T cell and CD4+CD8+ T cell stage. These data indicate that gravity plays a decisive role in the development of T cells.

[Changes of osteocalcin in bone and bone marrow in tail suspended rats]

OBJECTIVE

To study osteocalcin [correction of osteocakin] (OC) changes in bone and marrow and calcium deposition in bone and cartilage under simulated weightlessness.

METHOD

Twenty SD rats were randomly divided into 14 d and 28 d tail suspension group and 2 corresponding control groups. Histological samples were in situ hybridized and trichrome stained.

RESULT

OC expression of bone and marrow of rats were lower in tail suspended rats than that in the control (P<0.05). OC expression in 14 d tail suspended rats were higher than that in 28 d tail suspended group (P<0.05). Mineralization was inhibited, and demineralization of femur [correction of furmer] and cartilage mineralized matrix was prominent. Demineralization was more prominent in 28 d group.

CONCLUSION

OC levels in bone and marrow of rats were lower after tail suspension. Calcium deposition was inhibited in bone and cartilage. Demineralization was prominent after long term hindlimb unloading.

Changes in serum 1,25-dihydroxyvitamin D3 and mRNAs for osteocalcin and alkaline phosphatase in femur unloaded by tail suspension in rats

To elucidate the mechanism involved in the development of disuse atrophy of bone by skeletal unloading, changes in osteocalcin and alkaline phosphatase mRNAs, markers for bone formation, were studied in the hind limb bones of tail-suspended rats. Tail suspension for 8 and 14 days resulted in a significant decrease in osteocalcin mRNA in the femur when compared with age-matched non-suspended controls. Serum 1,25-dihydroxyvitamin D3 decreased to 60% of the control level after 8 days of skeletal unloading but regained almost normal levels over the next 7 days. Since it is known that vitamin D3 up regulates and glucocorticoid down regulates transcription of the osteocalcin gene, the endocrine response evoked by tail suspension may have aggravated the disuse atrophy caused by skeletal unloading in this study.

[Prophylaxis of the unfavorable shifts in mineral turnover in bones during extended exposure to the conditions reproducing the physiological effects of microgravity]

Effectiveness of the countermeasures and methods for mitigation of the unfavorable effects of microgravity on mineral turnover and properties of bones was evaluated in simulation experiments with animals (penal immobilization, suspension) and with participation of human subjects (37 to 120-d head-down bed rest). The experiments with rats were aimed at testing pharmaceutical preparations (bisphosphonates), determining doses, plan and way of administration. Preparations of this group differ considerably in their action on osteogenesis, mostly because of specifics of the chemical structure. Nonetheless, optimization of the course of treatment masked significantly side effects without detriment to the preventive action. Head-down bed rest was used to test effectiveness of physical exercises (PE) as a main countermeasure against the microgravity impacts. Both standard and experimental PE regimens were tested. Several groups of test-subjects combined PE with consumption of xidifon (a bisphosphonate). In addition, mineral supplements (potassium and calcium) were used. The PE + xidifon combination and regulation of mineral intake with foods was found to reduce calcium losses during 370-d bed rest and prevent a material degradation of strength of bone samples, and essentially rehabilitate shifts in the hormonal regulation of calcium turnover and calciuretic function of the kidney.