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PubMed2002

Effect of clinorotation on in vitro cultured explants of Mentha piperita L.

An in vitro culture system was used to study the influence of gravity on axillary shoot formation and adventitious root regeneration in Mentha piperita L. The direction of the gravity vector was altered by displacing stem node explants in different orientations. Also, microgravity conditions were simulated by rotating the explants on a horizontal clinostat so that the main axis of nodes was either parallel (Cpa) or perpendicular to the clinostat axis (Ccp and Ccf, centripetally and centrifugally oriented, respectively). Mint nodes were cultured on solidified Linsmaier and Skoog's medium [Physiol. Plant. 18 (1965) 100] adding a filter-sterilized aqueous solution of 2 mg/l benzyladenine (BA) in half of the cultures. The proliferation of axillary shoots as well as adventitious root formation were not affected by altering upright explant orientation. On the contrary clinorotation was able to modify plantlet development. In absence of BA, leaf width was hindered by Cpa treatment and penultimate internode length was enhanced by Ccp. Furthermore, a negative effect of Cpa treatment was observed in root length parameter, while Ccp increased the root number both in absence and in presence of BA. An effect strictly connected to clinorotation in presence of BA was the occurrence of hyperhydricity. Moreover, explants under clinorotation treatments switched their gravitropic response modifying shoot curvature.

Adenine↗
PubMed2003

[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.

Animals↗
PubMed2002

Effect of simulated microgravity on endocrine response to insulin-induced hypoglycemia in physically fit men.

Adaptation to microgravity is associated with alteration in some endocrine functions. In the present longitudinal study, the counterregulatory hormonal response to insulin-induced hypoglycemia (ITT, 0.1 IU/kg short acting insulin i. v.) was evaluated under simulated microgravity conditions in 15 physically fit subjects. ITT was performed at the beginning of the investigation, and again after completion of 6 weeks of endurance training and after a subsequent period of 4 days of head-down bed rest at a backward tilt of 6 degrees from the horizontal. Endurance training showed a significant increase in maximal aerobic capacity in previously well-trained subjects (increase by 12 %), as well as on attenuation of counterregulatory response of epinephrine to hypoglycemia. After 4 days of bed rest, basal concentrations of plasma norepinephrine was diminished (p < 0.002) and plasma renin activity was enhanced (p < 0.02). After bed rest, decreased responses of the two catecholamines (norepinephrine, p < 0.001; epinephrine, p < 0.001), growth hormone (p < 0.001), and cortisol (p < 0.05) were observed. Response of plasma renin activity after bed rest was increased (p < 0.01). This longitudinal study indicated that 4 days of bed rest in endurance-trained subjects induced increased response of PRA to hypoglycemia and attenuation of other counterregulatory neuroendocrine responses.

Adult↗
PubMed2001

Validity of microgravity simulation models on earth.

Many studies have used water immersion and head-down bed rest as experimental models to simulate responses to microgravity. However, some data collected during space missions are at variance or in contrast with observations collected from experimental models. These discrepancies could reflect incomplete knowledge of the characteristics inherent to each model. During water immersion, the hydrostatic pressure lowers the peripheral vascular capacity and causes increased thoracic blood volume and high vascular perfusion. In turn, these changes lead to high urinary flow, low vasomotor tone, and a high rate of water exchange between interstitium and plasma. In contrast, the increase in thoracic blood volume during a space mission is combined with stimulated orthosympathetic tone and lowered urine flow. During bed rest, body tissues are compressed by pressure from gravity, whereas microgravity causes a negative pressure around the body. The differences in renal function between space and experimental models appear to be explained by the physical forces affecting tissues and hemodynamics as well as by the changes secondary to these forces. These differences may help in selecting experimental models to study possible effects of microgravity.

Baroreflex↗
PubMed2000

Postural modulation of soleus H-reflex under simulated hypogravity by head-out water immersion in humans.

To test our hypothesis that somatosensory inputs would influence postural modulation of soleus H-reflex, eleven subjects were investigated under the head-out water immersion (HOWI) conditions. Subjects were supine or standing on a tilting bed in each condition. They were instructed to maintain an upright posture with both legs. The water was filled to the subject's neck level in a test tank to reduce 95% of the gravitational effect by buoyancy. Surface electromyography of the soleus and tibialis anterior was measured. The soleus H-reflex was elicited at a stimulation intensity of 1.05 times the motor threshold. The recruitment profile of the motor response was unchanged between the conditions. The background activities of the soleus and tibialis anterior were not detected in any condition. The peak-to-peak amplitude of the H-reflex was significantly different between the conditions while the stimulation intensity (small M size) was not different. The soleus H-reflex during standing was significantly decreased compared with being supine in the control condition, whereas it did not in the HOWI condition. It was concluded that somatosensory inputs due to gravity exert an influence on postural modulation of the soleus H-reflex to maintain static posture in humans.

Adult↗
PubMed1996

Animal models and their importance to human physiological responses in microgravity.

Two prominent theories to explain the physiological effects of microgravity relate to the cascade of changes associated with the cephalic shifts of fluids and the absence of tissue deformation forces. One-g experiments for humans used bed rest and the head-down tilt (HDT) method, while animal experiments have been conducted using the tail-suspended, head-down, and hindlimbs non-weightbearing model. Because of the success of the HDT approach with rats to simulate the gravitational effects on the musculoskeletal system exhibited by humans, the same model has been used to study the effects of gravity on the cardiopulmonary systems of humans and other vertebrates. Results to date indicate the model is effective in producing comparable changes associated with blood volume, erythropoiesis, cardiac mass, baroreceptor responsiveness, carbohydrate metabolism, post-flight VO2max, and post-flight cardiac output during exercise. Inherent with these results is the potential of the model to be useful in investigating responsible mechanisms. The suspension model has promise in understanding the capillary blood PO2 changes in space as well as the arterial PO2 changes in subjects participating in a HDT experiment. However, whether the model can provide insights on the up-or-down regulation of adrenoreceptors remains to be determined, and many investigators believe the HDT approach should not be followed to study gravitational influences on pulmonary function in either humans or animals. It was concluded that the tail-suspended animal model had sufficient merit to study in-flight and post-flight human physiological responses and mechanisms.

Animals↗
PubMed2000

Structural and functional remodeling of skeletal muscle microvasculature is induced by simulated microgravity.

Hindlimb unloading of rats results in a diminished ability of skeletal muscle arterioles to constrict in vitro and elevate vascular resistance in vivo. The purpose of the present study was to determine whether alterations in the mechanical environment (i.e., reduced fluid pressure and blood flow) of the vasculature in hindlimb skeletal muscles from 2-wk hindlimb-unloaded (HU) rats induces a structural remodeling of arterial microvessels that may account for these observations. Transverse cross sections were used to determine media cross-sectional area (CSA), wall thickness, outer perimeter, number of media nuclei, and vessel luminal diameter of feed arteries and first-order (1A) arterioles from soleus and the superficial portion of gastrocnemius muscles. Endothelium-dependent dilation (ACh) was also determined. Media CSA of resistance arteries was diminished by hindlimb unloading as a result of decreased media thickness (gastrocnemius muscle) or reduced vessel diameter (soleus muscle). ACh-induced dilation was diminished by 2 wk of hindlimb unloading in soleus 1A arterioles, but not in gastrocnemius 1A arterioles. These results indicate that structural remodeling and functional adaptations of the arterial microvasculature occur in skeletal muscles of the HU rat; the data suggest that these alterations may be induced by reductions in transmural pressure (gastrocnemius muscle) and wall shear stress (soleus muscle).

Animals↗
PubMed2001

MAPK and SRC-kinases control EGR-1 and NF-kappa B inductions by changes in mechanical environment in osteoblasts.

Bone loss occurs in microgravity whereas an increase in bone mass is observed after skeletal loading. This tissue adaptation involves changes in osteoblastic proliferation and differentiation whose mechanisms remain largely unknown. In this context, we investigated the expression and the nuclear translocation of Egr-1 and NF-kappa B, in a simulated microgravity model (clinostat) and in a model of mechanical strain (Flexcell). We performed RT-PCR and immunocytochemistry analyses at baseline and up to 2 h after stimulation (a mitogenic regimen, 1% stretch, 0.05 Hz, 10 min, or clinorotation 50 rpm, 10 min) in osteoblastic ROS17/2.8 cells. Egr-1 induction as well as NF-kappa B nuclear translocation were activated by mechanical changes. PKC downregulation and COX1/2 inhibition did not alter these inductions. In contrast, ERK1/2, p38(MAPK) and src-kinases pathways were differentially involved in both models. Thus, we demonstrated that changes in the mechanical environment induced an activation of Egr-1 and NF-kappa B with specific kinetics and involved various transduction pathways including MAPKs and src-kinases. These could partially explain the later alterations of proliferation observed.

Animals↗
PubMed1990

Actin filaments responsible for the location of the nucleus in the lentil statocyte are sensitive to gravity.

The location of the nucleus in statocytes or lentil roots grown: 1), at 1 g on the ground, 2), on a 1 g centrifuge in space, 3), in simulated microgravity on a slowly rotating clinostat (0.9 rmp) 4), in microgravity in space was investigated and statistically evaluated. In cells differentiated at 1 g on the ground, the nuclear membrane was almost in contact with the plasmalemma lining the proximal cell wall, whereas in statocytes of roots crown on the clinostat there was a distance of 0.47 micrometers (horizontal clinorotation) and or 0.76 micrometers (vertical clinorotation) between these membranes. However, in microgravity the nucleus was the most displaced, 0.87 micrometers from the proximal cell wall. Centrifugation of vertically grown roots in the root-tip direction showed that the threshold of centrifugal force to detach all nuclei from the proximal cell wall was about 40 g. In statocytes developed in the presence of cytochalasin B at 1 g the nuclei were sedimented on the amyloplasts at the distal cell pole, demonstrating that the location of the nucleus depends on actin filaments. The results obtained are in agreement with the hypothesis that gravity causes a tension of actin filaments and that this part of the cytoskeleton undergoes a relaxation in microgravity.

Actins↗
PubMed2001

Changes in vasoreactivity of rat pulmonary artery after 7 d tail-suspension.

OBJECTIVE: To clarify the effects of simulated microgravity on the local regulating function of the pulmonary circulation. METHOD: Rat tail-suspension (TS) was used as the animal model to simulate the effects of microgravity. The changes in responses of pulmonary artery to several vasoactive agents were determined by using in vitro vessel rings perfusion technique. RESULT: As for the endothelium-intact vessel rings from TS group compared with those from the control (C) group, the contractile responses of pulmonary artery to potassium chloride (KCl, 10 ~ 70 mmol/L) did not change obviously after 7 d tail-suspension, which were markedly diminished as to phenylephrine (PE, 10(-9) ~ 10(-5) mol/L). The vasodilatory responses to acetylcholine (ACh, 10(-9) ~ 10(-5) mol/L) were markedly enhanced, which did not change obviously as to captopril (Cap, 10(-5) ~ 3 x 10(-3) mol/L). The vasoreactivity of endothelium-removed pulmonary artery rings to all vasoactive agents did not change after 7 d tail-suspension as compared with those from control rats. CONCLUSION: The release of nitric oxide (NO) by rat pulmonary arterial endothelium was enhanced after 7 d tail-suspension. The vasodilatory function of pulmonary artery was enhanced.

Acetylcholine↗
PubMed2005

Use of animal models for space flight physiology studies, with special focus on the immune system.

Animal models have been used to study the effects of space flight on physiological systems. The animal models have been used because of the limited availability of human subjects for studies to be carried out in space as well as because of the need to carry out experiments requiring samples and experimental conditions that cannot be performed using humans. Experiments have been carried out in space using a variety of species, and included developmental biology studies. These species included rats, mice, non-human primates, fish, invertebrates, amphibians and insects. The species were chosen because they best fit the experimental conditions required for the experiments. Experiments with animals have also been carried out utilizing ground-based models that simulate some of the effects of exposure to space flight conditions. Most of the animal studies have generated results that parallel the effects of space flight on human physiological systems. Systems studied have included the neurovestibular system, the musculoskeletal system, the immune system, the neurological system, the hematological system, and the cardiovascular system. Hindlimb unloading, a ground-based model of some of the effects of space flight on the immune system, has been used to study the effects of space flight conditions on physiological parameters. For the immune system, exposure to hindlimb unloading has been shown to results in alterations of the immune system similar to those observed after space flight. This has permitted the development of experiments that demonstrated compromised resistance to infection in rodents maintained in the hindlimb unloading model as well as the beginning of studies to develop countermeasures to ameliorate or prevent such occurrences. Although there are limitations to the use of animal models for the effects of space flight on physiological systems, the animal models should prove very valuable in designing countermeasures for exploration class missions of the future.

Animals↗
PubMed2003

Measurement of nutritional status in simulated microgravity by bioelectrical impedance spectroscopy.

The potential of bioelectrical impedance spectroscopy (BIS) for assessing nutritional status in spaceflight was tested in two head-down-tilt bed-rest studies. BIS-predicted extracellular water (ECW), intracellular water (ICW), and total body water (TBW) measured using knee-elbow electrode placement were compared with deuterium and bromide dilution (DIL) volumes in healthy, 19- to 45-yr-old subjects. BIS was accurate during 44 h of head-down tilt with mean differences (BIS - DIL) of 0-0.1 kg for ECW, 0.3-0.5 for ICW, and 0.4-0.6 kg for TBW (n = 28). At 44 h, BIS followed the within-individual change in body water compartments with a relative prediction error (standard error of the estimate/baseline volume) of 2.0-3.6% of water space. In the second study, BIS did not detect an acute decrease (-1.41 +/- 0.91 kg) in ICW secondary to 48 h of a protein-free, 800 kcal/day diet (n = 18). BIS's insensitivity to ICW losses may be because they were predominantly (65%) localized to the trunk and/or because there was a general failure of BIS to measure ICW independently of ECW and TBW. BIS may have potential for measuring nutritional status during spaceflight, but its limitations in precision and insensitivity to acute ICW changes warrant further validation studies.

Adult↗
PubMed2002

Rhythmicity of engraftment and altered cell cycle kinetics of cytokine-cultured murine marrow in simulated microgravity compared with static cultures.

Space flight with associated microgravity is complicated by "astronaut's anemia" and other hematologic abnormalities. Altered erythroid differentiation, red cell survival, plasma volume, and progenitor numbers have been reported. We studied the impact of microgravity on engraftable stem cells, culturing marrow cells in rotary wall vessel (RWV) culture chambers mimicking microgravity and in normal gravity nonadherent Teflon bottles. A quantitative competitive engraftment technique was assessed under both conditions in lethally irradiated hosts. We assessed 8-wk engraftable stem cells over a period spanning at least one cell cycle for cytokine (FLT-3 ligand, thrombopoietin [TPO], steel factor)-activated marrow stem cells. Engraftable stem cells were supported out to 56 h under microgravity conditions, and this support was superior to that seen in normal-gravity Teflon bottle cultures out to 40 h, with Teflon bottle culture support superior to RWV from 40 to 56 h. A nadir of stem cell number was seen at 40 h in Teflon and 48 h in RWV, suggesting altered marrow stem cell cycle kinetics under microgravity. This is the first study of engraftable stem cells under microgravity conditions, and the differences between microgravity and normal gravity cultures may present opportunities for unique future stem cell expansion strategies.

Animals↗
PubMed1998

Measurement of intraocular pressure by both invasive and noninvasive techniques in rabbits exposed to head-down tilt.

This study investigates changes in intraocular pressure (IOP) in rabbits during head-down tilt (HDT), which is commonly used as an experimental model to simulate microgravity. IOP was measured by the needle insertion technique (IOPNEEDLE) and Tono-pen tonometry (IOPTONO-PEN). Although the absolute value of the IOPTONO-PEN was significantly smaller than that of the IOPNEEDLE, a significant correlation (r = 0.99) was observed between them. A linear regression analysis yielded an equation as follows: IOPTONO-PEN = 0. 67 IOPNEEDLE - 0.67. Both the IOPNEEDLE and the IOPTONO-PEN changed depending on the tilt angle. Tilting from horizontal (0 degrees) to 75 degrees head-down increased the IOPNEEDLE and the IOPTONO-PEN by 7.3 +/- 0.8 (mean +/- SEM) mmHg and 4.4 +/- 1.3 mmHg. The IOPNEEDLE elevated from 13.1 +/- 1.3 to 16.9 +/- 1.0 mmHg immediately after the onset of 45 degrees HDT and then gradually declined. The value of the IOPNEEDLE during 8 h of HDT was significantly higher than the value in the control animals, which were kept at the horizontal prone position throughout the experiment. Similar findings were observed in the IOPTONO-PEN. These results suggest that the needle insertion technique and the Tono-pen tonometry are both useful for measuring IOP in rabbits.

Animals↗
PubMed2001

Effects of simulated microgravity on metabolic activities related to DNA damage and repair in lymphoblastoid cells.

We adopted a simple experimental framework to follow the dependence of structural aberrations and the modifications in selected metabolic processes correlated with the exposure of cells to microgravity. Alterations to the cellular metabolism induced by exposure to microgravity are evidentiated in the modification of PARP activity (strongly dependent to the presence of DNA damages and to the altered gene expression), in the modification of the repair ability and in the cell's energy homeostasis (NAD and ATP). Cells are exposed continuously to microgravity in a Random Positioning Machine (RPM) in complete medium for 48 hours. At the end of this period a part of these cells are immediately analysed for the parameters reported above and the remaining were furtherly incubated in standard laboratory conditions to document eventual defects during the phases of the recovery process. A part of cells, just after exposure to microgravity, were also subjected to treatment with a strong damaging agent, KBrO3, and these cells were subsequently analyzed. This final treatment was meant to amplify the eventual deficiencies experienced by microgravity-exposed cells in the DNA repair process also in dependence with the alterated metabolic conditions resulting after the exposure to microgravity.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2001

Ontogeny of plants under various gravity condition.

The results of experiments performed under conditions of microgravity (MG) or under its simulation on the horizontal clinostat (HC) with the callus, seedlings of various species and embryogenic structures have revealed a definite role of gravity as an ecological factor in the processes of cytomorphogenesis, growth, and development. The transformation of differentiated somatic cells of arabidopsis seed into undifferentiated callus was not inhibited under MG, though modifications of the whole callus morphology and of mean cell and nucleus size were observed. The morphogenesis of polar structures such as root-hair bearing cells of Lactuca primary root has been shown to be modified in the course of differentiation under mass acceleration diminished below 0.1 g. Seed germination and seedling morphogenesis under MG follow their normal course, but a significant stimulation of shoot growth with no effect on primary root growth has been determined. A successful in vitro regeneration of Nicotiana tabacum plantlets from leaf cells and subsequent formation of shoots and roots on a continuously rotating HC as well as the formation of viable seeds during seed-to-seed growth of Arabidopsis plants under MG have indicated that gravity plays but a limited role in the processes of embryogenesis and organogenesis.

Arabidopsis↗
PubMed2000

Stress-compensation by a food supplement based on yeast plasmolysate in mitogen-activated T lymphocytes under simulated low-gravity.

T lymphocyte function is strongly depressed in vitro and in vivo under low-g conditions in space as well as simulated in clinostat. Here we describe the effect of a food supplement based on yeast plasmolysate on T cells activated in vitro with Concanavalin A and cultured in a random positioning machine. The mitotic index was measured by 3H-thymidine incorporation into DNA, the expression of activation markers CD25, CD69 and HLA-DR on the cell surface by cytofluorimetry and the secretion of the IL-2R by an enzyme immunoassay. Our data indicate that the food supplement used is capable to modulate T lymphocyte function. The addition of the food supplement increased the expression of activation markers in activated and non-activated cells. Cultivation under low-gravity conditions reduced the expression of the activation markers, but this expression was partly restored or even increased upon addition of yeast plasmolysate. On the other hand, cell proliferation and secretion of soluble IL-2 receptor was reduced after addition of the food supplement in all samples.

Antigens, CD↗
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↗