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PubMedDate not supplied

[Changes in several indicators of blood rheology in experiments simulating weightlessness].

Changes in blood rheological parameters of 21 male volunteers, aged 25-37 years, were studied. The test subjects were subdivided into three groups. Nine subjects of Group 1 were exposed to head-down tilting (-8 degrees) for 14 days, six subjects of Group 2 were exposed to 7-day continuous immersion, and six subjects of Group 3 to intermittent immersion. During head-down tilting the apparent viscosity and hematocrit and then caisson viscosity increased. By day 7 the coefficient of red blood cell aggregation decreased significantly. These changes persisted till the end of the tilt study. The above rheological parameters returned to normal three days after the exposure. During continuous immersion the apparent viscosity showed the largest changes. Other specific changes included a moderate decrease of hematocrit, lack of significant changes in the yield limit of blood and a tendency towards an increase in the erythrocyte aggregation coefficient. Three days after the exposure the blood viscosity was much higher than before the study. During intermittent immersion rheological changes were induced by the first 36-hour exposure when shifts in blood viscosity and other parameters were most significant. It should be noted that following this exposure 72 hours of normal motor activity did not result in the normalization of the above rheological parameters.

Adolescent↗
PubMedDate not supplied

[Biogenic amines in the small intestines in guinea pigs in simulated weightlessness and vibration].

The dynamics of changes in epinephrine (E), norepinephrine (NE), dopamine (DA), serotonin (5-HT) and its metabolite 5-HIAA in the duodenal and iliac wall was studied in the initial period of support unloading (the "dry" immersion method) and general low frequency vibration (LFV). It was found that 15-min unloading led to a sharp increase in 5-HT and DA in the duodenum, accompanied by an elevation in total electrical activity of smooth muscles, to a decrease in E, NE, and DA and, in contrast, to an increase in 5-HT and 5-HIAA in the ileum. Normalization of monoamine metabolism observed 2 h after the beginning of the unload 4 hour later was followed by inactivation of duodenal serotoninergic structures and iliac adrenergic structures. The LFV induced mostly the opposite response, decreasing 5-HT in the duodenum with accumulation of E and NE in it, and a more marked activation of inhibitory adrenergic innervation of the ileum.

Animals↗
PubMed2003

[Changes of bone morphogenesis proteins and transforming growth factor-beta in hind-limb bones of 21 d tail-suspended rats].

OBJECTIVE: To investigate changes of bone morphogenesis proteins (BMP), transforming growth [correction of grouth] factors-beta (TGF-beta) in tibia and the growing of femur in tail-suspended rats after 21 d simulated weightlessness. METHOD: Fourteen male SD rats were randomly divided into control group (CON) and tall-suspension group (TS). After 21 d tail-suspension, basic physical parameters of the femur were measured; changes of BMP, TGF-beta in tibia were assayed by immunohistochemical method. RESULT: During 21 d tail-suspension, all rats grew well without apparent stress reaction. After 21 d weightlessness simulation, wet weight, dried weight, ash, diameter and density of femur in TS group declined significantly (P<0.01). Immunohistochemical results of tibia showed that both BMP and TGF-beta declined in tissues from all regions of the tibia. CONCLUSION: After 21 d tall-suspension, the growth of rat's weight bearing bones were suppressed, production and secretion of BMP and TGF-beta was holdback.

Animals↗
PubMed1995

Cardiovascular variability and baroreceptor reflex sensitivity over a 14-day tail suspension in rats.

To verify whether a long-term weightlessness simulation was associated with development of cardiovascular deconditioning, male Wistar rats were tail suspended for 13 days and then removed for a 24-h recovery. Blood pressure (BP) and heart rate (HR) responses, their spectral properties, and the pharmacologically tested baroreceptor reflex sensitivity were studied throughout the suspension period and after removal from the tail suspension device. BP, HR, and their variability were not altered over the experimental period, and there were no indications of orthostatic intolerance on release from head-down suspension. Spectral properties of BP and HR were unchanged during the experiment, and tail suspension did not induce modifications in the baroreceptor reflex sensitivity. These results taken together suggest that cardiovascular deconditioning may not be developed even after long-term hindlimb suspension in rats, in contrast to humans exposed to actual or simulated weightlessness. Our results raise issue with the use of tail-suspended rats as a valid model for the study of alterations in cardiovascular function induced by spaceflight in humans.

Animals↗
PubMed2000

[Effects of 6-degree head-down bed rest on physical fitness].

We investigated changes in enduring physical fitness during a ground-based weightlessness simulation of 6-degree head-down bed rest (HDBR). Ten healthy volunteers participated in the 6 days of HDBR. In each, their physique, muscular strength, physical fitness, cardiovascular function, and hematocrit were measured before and after HDBR. The results are as follows: (1) Thigh extensor power: the cross-sectional areas of the thigh and leg muscles were significantly decreased after HDBR, but recovered immediately afterwards. (2) Hand grip power and instantaneous power: the body response time showed no significant change before and after HDBR. (3) High physical capacity was correlated with a greater decrease in physical capacity after HDBR. (4) Remarkable functional depression appeared in the cardiovascular system compared with the gas exchange system as measured by the enduring physical fitness test. (5) The functional depression in the cardiovascular system lasted for more than 3 days after HDBR. (6) Six days of HDBR had little influence on physical fitness attributable to the inactivity and seemed to effectively simulate weightlessness for the cardiovascular system.

Activities of Daily Living↗
PubMed2002

Acetylcholinesterase activity in soleus muscle intrafusal and extrafusal fibres in tail suspended rats.

Objective. To explore the mechanisms involved in muscle atrophy and conversion of the fiber types induced by simulated weightlessness. Method. Weightlessness was simulated by tail suspension of female rats. Intrafusal and extrafusal fibers of soleus muscles in the rat were examined histochemically for their activity of acetylcholinesterase (AChE) and succinic dehydrogenase (SDH) in 7 d, 14 d, 21 d tail-suspended groups and control groups. Result. Staining for succinic dehydrogenase showed that simulated weightlessness caused obvious atrophy and change in fiber type composition in soleus muscle, with decrease of the proportion of type I fiber and increase of type II fiber. Acetylcholinesterase activities of intrafusal and extrafusal fibers were both decreased significantly after 21 d tail suspension. Conclusion. Simulated weightlessness could induce decrease of AChE activity in neuromuscular junctions, which might be linked with decrease in motor neuron activity.

Acetylcholinesterase↗
PubMed2004

Effects of tail suspension on electrophysiological characteristics of muscle spindles in isolated rat soleus muscle.

OBJECTIVE: To study changes in electrophysiological characteristics of muscle spindles induced by simulated weightlessness in isolated rats soleus. METHOD: Weightlessness was simulated by tail-suspension in female rats. Using electro-physiological technique, the spontaneous discharge of muscle spindle and its response to ramp-and-hold stretch were observed in isolated soleus of 7 d, 14 d tail-suspended and control rats. RESULT: Soleus muscle spindles of rat manifest a sharp decrease in spontaneous discharge frequency and the response to ramp-and-hold stretch after 7 d tail-suspension. More significant changes were observed in rats after 14 d tail-suspension. CONCLUSION: Simulated weightlessness could induce time-related changes in electrophysiological characteristics of soleus muscle spindles in rat.

Animals↗
PubMed1997

Evaluation of the three-dimensional clinostat as a simulator of weightlessness.

Concerns regarding the reliability of slow-and fast-rotating uni-axial clinostats in simulating weightlessness have induced the construction of devices considered to simulate weightlessness more adequately. A new three-dimensional (3-D) clinostat equipped with two rotation axes placed at right angles has been constructed. In the clinostat, the rotation achieved with two motors is computer-controlled and monitored with encoders attached to the motors. By rotating plants three-dimensionally at random rates on the clinostat, their dynamic stimulation by gravity in every direction can be eliminated. Some of the vegetative growth phases of plants dependent on the gravity vector, such as morphogenesis, are shown to be influenced by rotation on the 3-D clinostat. The validity of 3-D clinostatting has been evaluated by comparing structural parameters of cress roots and Chara rhizoids obtained under real microgravity with those obtained after 3-D clinostatting. The parameters analyzed up to now (organization of the root cap, integrity and polarity of statocytes, dislocation of statoliths, amount of starch and ER) demonstrate that the 3-D clinostat is a valuable device for simulating weightlessness.

Plant Physiological Phenomena↗
PubMed1986

Gravisensitivity of the acellular slime mold Physarum polycephalum demonstrated on the fast-rotating clinostat.

The acellular slime mold Physarum polycephalum was used to investigate a postulated general gravisensitivity of cells. Physarum was subjected i) to a rotation on the fast-rotating clinostat, which enables the simulation of weightlessness (0 g), and ii) to single horizontal turns of 180 degrees. On the fast-rotating clinostat the response consists of a frequency increase in radial contractile activity, an oscillation of the mean values (frequency regulation phenomena) and an increase in standard deviation. A combination of 0 g and respiration impediment inhibits the response to 0 g, i. e., the frequency increase in radial contractile activity during weightlessness simulation. Turning the specimens horizontally about 180 degrees in a normally positioned light microscope also leads to a frequency increase in radial contractile activity, but the temporal pattern of the frequency increase differs in comparison to the experiments performed on the clinostat during weightlessness simulation. These results demonstrate the occurrence of gravisensitivity in Physarum polvcephalum. Regulation phenomena and the possible role of mitochondria in graviperception are discussed.

Animals↗
PubMed2006

[Effects of inosine injection in expression of myosin heavy chain in intrafusal and extrafusal myofibers in soleus muscle of tail-suspended rats].

AIM: To study the effects of inosine on myosin heavy chain (MHC) activity in rats soleus muscle after tail-suspension. METHODS: Weightlessness was simulated by tail-suspension of rats. Using immunohistochemistry technique, changes of expression of MHC in intrafusal and extrafusal fibers in soleus muscle were detected. RESULTS: Expression of fast MHC in intrafusal and extrafusal fibers in soleus muscle increased after 14 d of simulated weightlessness, whereas in tail-suspended rats given inosine, the expression of fast MHC was not detected. CONCLUSION: Inosine could counteract the changes in expression of MHC in intrafusal and extrafusal fibers of rats soleus under simulated weightless situation.

Animals↗
PubMed2004

[Effects of high frequency vibration on expression of myosin heavy chain (MHC) in intrafusal and extrafusal fibers in soleus muscles of tail-suspended rats].

OBJECTIVE: To study the effects of high frequency vibration on expression of myosin heavy chain (MHC) in intrafusal and extrafusal fibers in soleus muscles of tail-suspended rats. METHOD: Weightlessness was simulated by tail suspension of female rats. Using immunohistochemistry technique, changes of expression of MHC in intrafusal and extrafusal fibers of soleus muscles were detected. RESULT: Expression of fast MHC in intrafusal and extrafusal fibers of soleus muscles increased during 7 d of simulated weightlessness, whereas during 7 d of tail suspension plus high frequency vibration, these changes were not detected. CONCLUSION: High frequency vibration can counteract the changes in expression of MHC in intrafusal and extrafusal fibers of rats soleus under muscles of rats in simulated weightlessness situation.

Animals↗
PubMed1999

Simulated weightlessness-induced attenuation of testosterone production may be responsible for bone loss.

This study examined the effects of simulated weightlessness on serum hormone levels and their relationship to bone mineral density (BMD). The tail-suspended (i.e., hindlimb suspended, HLS) rat model was used to simulate weightless conditions through hindlimb unloading to assess changes in hormonal profile and the associated bone loss. In the first study, 24 adult male rats were assigned to two groups with 12 rats being HLS for 12 d, and the remaining 12 rats serving as ground controls. On d 0, 6, and 12, blood samples were taken to estimate circulating hormone levels. HLS rats had significant reductions in testosterone, 1,25 (OH)2 vitamin D, and thyroxine levels by d 6 (p<0.01); their testosterone levels were almost undetectable by d 12 (p<0.001). Serum cortisol levels in these rats were elevated on d 6 (p<0.02), but returned to normal levels by d 12. No changes were observed with serum ionized calcium and other hormones examined, as well as the body weights, and weights of thymus, heart, and brain. In the second study, eight rats were ground controls, while an additional eight rats were HLS for 12 d before being removed from tail-suspension and maintained for a further 30 d. Blood samples were collected every 6th d for 42 d. This study showed that both serum thyroxine and 1,25(OH)2 vitamin D levels returned to normal levels soon after hind limb unweighting, while serum testosterone levels matched normal levels only after a further 3-4 wk. These studies showed a significant decrease of femur weights, but not weights of humeri in HLS rats suggesting that this is a specific effect on unloaded bones. On d 12 in both studies, a significant reduction in the lumbar spine (p<0.05) and the femoral neck (p<0.01) BMD appeared in HLS rats. This was confirmed in the second study, where HLS led to a significant decrease in BMD even extending to d 42. Previous studies have shown that space flight and tail-suspension lead to marked reductions in bone formation with little effect on bone resorption. Recently, we reported that androgen replacement can indeed prevent bone losses in this animal model. Therefore, it seems logical to propose that the significant decreases of serum testosterone observed in these tail-suspended animals are, at least in part, responsible for the losses of BMD seen in their affected weight-bearing bones (i.e., lumbar spine and the femur). Considering that 1. testosterone is anabolic to osteoblasts and also decreases the rate of bone turnover 2. serum testosterone levels are markedly suppressed in simulated weightlessness, and 3. testosterone replacement therapy prevented the bone loss in HLS rats, we propose that the testosterone deficiency in this animal model is related to their bone loss.

Animals↗
PubMed1997

Analysis of heart rate variability and its application.

Heart rate variability (HRV) has considerable potentials in assessing the role of autonomic nervous system fluctuations in healthy individuals and patients. This paper reviews the analytical methods of HRV and its application. HRV is a useful parameter for predicting cardiac risk after acute myocardial infarction, and an early warning sign of diabetes neuropath in clinical medicine. In space medical studies, HRV analysis have been used to assess changes in autonomic regulation after weightlessness or simulated weightlessness, evaluate tolerance in various stress test, study regulatory mechanisms of cardiovascular system, and assess the effect of countermeasure against weightlessness.

Aerospace Medicine↗