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PubMed2006

[Effect of tail-suspension on the reproduction of adult male rats].

OBJECTIVE: To study the effects on the male reproduction in adult male rats and its mechanisms through simulated weightlessness using tail-suspension, in order to do a basic works of exploring the effects on human being's reproduction in outer space. METHODS: Forty Spraque-Dawley adult male rats were randomly divided into four groups, two experimental groups and two control groups. Rats in the two experimental groups were tail-suspended for 14 d and 28 d respectively, then we examined the weight and morphology of testis, the quality and amount of sperm, also tested the serum hormone by radioimmunoassay and analyzed apoptosis rate of testicular cells by TUNEL in the experimental rats and control rats. RESULTS: After tail-suspension, the weight of testis, the sperm count and sperm motility significantly decreased (P <0.05), while the apoptosis rate of testicular cells and the amount of abnormal sperm markedly increased (P <0.05). The content of testosterone significantly decreased (P <0.05), but the contents of FSH and LH mildly increased (P > 0.05). These changes were not significant between two experimental groups (P > 0.05). In addition, the seminiferous tubules became atrophy with the reduction of the layers of seminiferous epithelium, and sperm amount in lumens of seminiferous tubules decreased in experimental groups. The above were more remarkable in the 28 d experimental group. CONCLUSION: Simulating weightlessness has a harmful effect on reproduction of adult male rats. These may be caused by inducing apoptosis. The blocking apoptosis of testicular cells may be useful in improving the harmful effect.

Animals↗
PubMed1994

Early development of Xenopus embryos is affected by simulated gravity.

Early amphibian (Xenopus laevis) development under clinostat-simulated weightlessness and centrifuge-simulated hypergravity was studied. The results revealed significant effects on (i) "morphological patterning" such as the cleavage furrow pattern in the vegetal hemisphere at the eight-cell stage and the shape of the dorsal lip in early gastrulae and (ii) "the timing of embryonic events" such as the third cleavage furrow completion and the dorsal lip appearance. Substantial variations in sensitivity to simulated force fields were observed, which should be considered in interpreting spaceflight data.

Animals↗
PubMed1994

Protozoa as model systems for the study of cellular responses to altered gravity conditions.

The orientation behavior of Paramecium changed in a similar way after transition to conditions of free-fall in a sounding rocket and after transition to conditions of simulated weightlessness on a fast rotating clinostat. After a period of residual orientation, Paramecium cells distributed themselves randomly 80 s (120 s) after onset of free-fall (simulated weightlessness). Swimming velocity increased significantly; however, the increase was transient and subsided after 3 min in the rocket experiments, while the velocity remained enhanced even during 2 h of rotation on a fast clinostat. Trichocysts were present and without morphological changes in Paramecium cells which had been exposed to a rocket flight, as well as to fast or slow rotation on a clinostat. Regeneration of the oral apparatus of Stentor and morphogenesis of Eufolliculina proceeded normally on the clinostat. The results demonstrate that the clinostat is a useful tool to simulate the conditions of weightlessness on earth and to detect gravisensitive cellular functions.

Animals↗
PubMed1999

[Alterations of arterial vasoconstrictor responsiveness in rats during and after tail-suspension].

Objective. To characterize the time course of alterations in vasoconstrictor properties of arteries during simulated weightlessness, and to examine whether these alterations are reversible. Method. The tail-suspended rat model was used to simulate weightlessness, and the alterations in vasoconstrictor response were examined in vitro using isolated arterial rings. Result. Compared with that of controls, contractile tension evoked by KCl and phenylephrine (PE) were lower in abdominal aortic, mesenteric and femoral arterial rings from 2 wk tail-suspended rats (P<0.05); after 4 wk tail-suspension, the responses of mesenteric and femoral arterial rings to KCl or PE were further decreased (P<0.05); but contraction responses of arterial rings from 8 wk tail-suspended rats were similar to that of 4 wk simulated microgravity rats. The reversibility of altered arterial vasoreactivity after 4 wk tail-suspension was observed for 5 wk. Vasoreactivity of abdominal aortic rings was recovered after first week of recovery, but it took five weeks that altered vasoreactivity of mesenteric and femoral artery got back to normal. Conclusion. The alterations in constrictor properties of arteries are dependent on both the duration of tail-suspension and the position of artery, the diminished vasoconstrictor properties appear to reach a new steady state after 4 wk tail-suspension, and the changes are reversible.

Animals↗
PubMed2006

Induction of three-dimensional assembly and increase in apoptosis of human endothelial cells by simulated microgravity: impact of vascular endothelial growth factor.

Endothelial cells play a crucial role in the pathogenesis of many diseases and are highly sensitive to low gravity conditions. Using a three-dimensional random positioning machine (clinostat) we investigated effects of simulated weightlessness on the human EA.hy926 cell line (4, 12, 24, 48 and 72 h) and addressed the impact of exposure to VEGF (10 ng/ml). Simulated microgravity resulted in an increase in extracellular matrix proteins (ECMP) and altered cytoskeletal components such as microtubules (alpha-tubulin) and intermediate filaments (cytokeratin). Within the initial 4 h, both simulated microgravity and VEGF, alone, enhanced the expression of ECMP (collagen type I, fibronectin, osteopontin, laminin) and flk-1 protein. Synergistic effects between microgravity and VEGF were not seen. After 12 h, microgravity further enhanced all proteins mentioned above. Moreover, clinorotated endothelial cells showed morphological and biochemical signs of apoptosis after 4 h, which were further increased after 72 h. VEGF significantly attenuated apoptosis as demonstrated by DAPI staining, TUNEL flow cytometry and electron microscopy. Caspase-3, Bax, Fas, and 85-kDa apoptosis-related cleavage fragments were clearly reduced by VEGF. After 72 h, most surviving endothelial cells had assembled to three-dimensional tubular structures. Simulated weightlessness induced apoptosis and increased the amount of ECMP. VEGF develops a cell-protective influence on endothelial cells exposed to simulated microgravity.

Apoptosis↗
PubMed2001

[The dynamic changes of NOSmRNA in endothelial cells of aortae and pulmonary arteries in rats under tail suspension].

Objective. Through the observations of dynamic changes of eNOSmRNA and iNOSmRNA in arterial endothelial cells of systematic circulation and pulmonary circulation under simulated weightlessness, to collect some data for studies of the adaptive mechanisms of local regulation in arterial systems. Method. Wistar rats were -30 degrees tail suspended to simulate the effects of weightlessness. The rats were randomly divided into three groups: control group (CON), 7-day tail suspension group (TS7) and 14-day tail suspension group (TS14). Changes of NOSmRNA expresses in endothelial cells of the thoracic aortae and pulmonary arteries were observed with in situ hybridization technique. Result. The eNOSmRNA and iNOSmRNA of thoracic aortic and pulmonary arterial endothelial cells in TS7 rats increased very significantly. The eNOSmRNA of thoracic aortic endothelial cells from TS14 rats returned to control level, but remained very significantly increased in pulmonary arteries. The iNOSmRNA in pulmonary arterial endothelial cells from TS14 rats decreased very significantly, but that in thoracic aortae returned to the control level. Conclusion. The responses of eNOSmRNA and iNOSmRNA in arterial endothelial cells of systematic circulation to tail suspension were similar, but they were different in pulmonary arterial endothelial cells, which might be due to the difference in the peak course of the shift of fluid from lower body entering the pulmonary or systematic circulation during initial period of simulated weightlessness. It could be a kind of important sign of depressed local regulative function under simulated weightlessness and might contribute to orthostatic intolerance after simulated weightlessness.

Animals↗
PubMedDate not supplied

Effect of simulated and real weightlessness on early regeneration stages of Brassica napus protoplasts.

Results from experiments using protoplasts in space, performed on the Biokosmos 9 satellite in 1989 and on the Space Shuttle on the IML-1-mission in 1992 and S/MM-03 in 1996, are presented. This paper focuses on the observation that the regeneration capacity of protoplasts is lower under micro-g conditions than under 1 g conditions. These aspects have been difficult to interpret and raise new questions about the mechanisms behind the observed effects. In an effort to try to find a key element to the poor regeneration capacity, ground-based studies were initiated focusing on the effect of the variable organization and quantity of corticular microtubules (CMTs) as a consequence of short periods of real and simulated weightlessness. The new results demonstrated the capacity of protoplasts to enter division, confirming the findings in space that this was affected by gravity. The percentage of dividing cells significantly decreased as a result of exposure to simulated weightlessness on a 2-D clinostat. Similar observations were made when comparing the wall components, which confirmed that the reconstitution of the cell wall was retarded under both space conditions and simulated weightlessness. The peroxidase activity in protoplasts exposed to microgravity was slightly decreased in both 0 g and 1 g flight samples compared with the ground controls, whereas activity in the protoplasts exposed to simulated weightlessness was similar to activity in the 1 g control. The observation that protoplasts had randomized and more sparse corticular microtubules when exposed to various forms of simulated and real weightlessness on a free-fall machine on the ground could indicate that the low division capacity in 0 g protoplasts was correlated with an abnormal CMT array in these protoplasts. This study has increased our knowledge of the more basic biochemical and cell biological aspects of g effects. This is an important link in preparation for the new space era, when it will be possible to follow the growth of single cells and tissue cultures for generations under microgravity conditions on the new International Space Station, which will be functional on a permanent basis from the year 2003.

Brassica napus↗
PubMed1999

Different responses of cerebral vessels to -30 degrees head-down tilt in humans.

This study explored changes of the cerebral circulation and evaluated the responses to weightlessness in 12 volunteers (18-22 yr of age). The velocities, diameters and blood flow volume of the common carotid artery (CCA), internal carotid artery (ICA), vertebral artery (VA) and internal jugular vein (IJV) were measured with color Doppler echogram before and during simulated weightlessness. -30 degrees head-down tilt (HDT) for 45 min was used as a weightlessness simulation model. When the subjects' positions were changed from the supine to -30 degrees HDT, blood flow velocities along the CCA, ICA and IJV decreased significantly (p< 0.05), and their diameters were increased. The subjects were divided into two groups according to measured changes in flow volume of the ICA and IJV: group I with a net in-flow of cerebral blood flow (CBF) and group II with a net out-flow of CBF during HDT. Symptoms were recorded in the two groups during HDT (nasal congestion, sensation of head fullness, headache, and others) and graded on a four-point scale, from absent to serious. Results showed that group I had a higher symptoms score while group II had a lower symptoms score. Although this difference did not reach statistical significance, it suggests that cerebral blood flow changes may be partly responsible for the symptoms observed in subjects during HDT.

Adolescent↗
PubMed2000

A comparison of autonomic responses in humans induced by two simulation models of weightlessness: lower body positive pressure and 6 degrees head-down tilt.

Six-degree head-down tilt (HDT) is well accepted as an effective weightlessness model in humans. However, some researchers utilized lower body positive pressure (LBPP) to simulate the cardiovascular and renal effects of a decreased gravitational stress. In order to determine whether LBPP was a suitable model for simulated weightlessness, we compared the differences between these two methods. Ten healthy males, aged 21-41 years, were subjected to graded LBPP at 10, 20 and 30 mmHg, as well as 6 degrees HDT. Muscle sympathetic nerve activity (MSNA) was microneurographically recorded from the tibial nerve along with cardiovascular variables. We found that MSNA decreased by 27% to a similar extent both at low levels of LBPP (10 and 20 mmHg) and HDT. However, at a high level of LBPP (30 mmHg), MSNA tended to increase. Mean arterial pressure was elevated significantly by 11% (10 mmHg) at 30 mmHg LBPP, but remained unchanged at low levels of LBPP and HDT. Heart rate did not change during the entire LBPP and HDT procedures. Total peripheral resistance markedly increased by 36% at 30 mmHg LBPP, but decreased by 9% at HDT. Both stroke volume and cardiac output tended to decrease at 30 mmHg LBPP, but increased at HDT. These results suggest that although both LBPP and HDT induce fluid shifts from the lower body toward the thoracic compartment, autonomic responses are different, especially at LBPP greater than 20 mmHg. We note that high levels of LBPP (>20 mmHg) activate not only cardiopulmonary and arterial baroreflexes, but also intramuscular mechanoreflexes, while 6 degrees HDT only activates cardiopulmonary baroreflexes. We conclude that LBPP is not a suitable model for simulated weightlessness in humans.

Adult↗
PubMed1994

Autonomic responses to environmental stimuli in human body.

The author reviewed in this paper current microneurographic findings on the responses of muscle sympathetic nerve activity (MSNA) and skin sympathetic nerve activity (SSNA) to the environment in humans with special reference to vibration-induced white finger (VWF). 1) MSNA was enhanced by +Gz gravitational input, while being suppressed by simulated weightlessness through the baroreflex mechanism to maintain hemodynamic homeostasis. 2) MSNA was enhanced by hypobaric hypoxia through the chemoreflex mechanism. 3) SSNA was lowest under thermoneutral ambient temperature condition. Sudomotor component of SSNA increased under hot ambient temperature, while vasomotor component of SSNA increased under cold ambient temperature. 4) MSNA and vasomotor component of SSNA increased by local cold stimuli such as when a hand was immersed into cold water. 5) SSNA was enhanced by local vibration of the human body. The vibratory frequency of 60 Hz was the most effective for vibration-induced SSNA response. With a constant vibratory frequency of 60 Hz, SSNA increased depending on the vibratory acceleration. MSNA was not enhanced by local vibration of the body. 6) SSNA was markedly enhanced by combined stimuli of local vibration and noise. 7) MSNA increased during handgrip exercise, presumably depending on afferent inputs from muscle metaboreceptors. 8) The sympathetic response to environmental stress was markedly influenced by aging. The basal level of MSNA increased with aging, while the MSNA responsiveness to gravitational stress became reduced by aging. MSNA responsiveness to simulated weightlessness was also reduced by aging. 9) Vibration-induced white finger may be related to complex autonomic dysfunctions including excessive somato-sympathetic reflex induced by local vibration, cold stimuli and handgrip exercise. Gravity-dependent sympathetic nerve responses and the influence of aging may also contribute to the underlying mechanisms of VWF.

Environmental Health↗
PubMed1992

Cardiopulmonary function during 10 days of head-down tilt bedrest.

Pulmonary and cardiovascular responses to simulated weightlessness, i. e. 6 degrees head-down tilt bedrest (HDT) were investigated in six healthy male volunteers (mean age 26 yrs). Pulmonary diffusing capacity, functional residual capacity, pulmonary capillary blood flow, and lung tissue volume were measured by inert gas rebreathing. Heart rate and mean arterial blood pressure were obtained from finger blood pressure readings using a plethysmographic technique (Finapres). The short-term (20 min) response to HDT consisted of a 22% increase in pulmonary blood flow, and 13% and 31% falls in blood pressure and heart rate relative to standing. Functional residual capacity fell by 33%, while lung tissue volume increased insignificantly. Subsequent measurements during 10 days of HDT and 5 days of recovery revealed no further changes in lung volume, lung tissue volume, or blood pressure. However, diffusing capacity fell gradually and remained 4%-5% below baseline values after the 7th day of bedrest and during recovery (p less than 0.05). Pulmonary blood flow decreased by 16% during head-down bedrest and recovered partially within the following 5 days (p less than 0.05). We conclude that during and after simulated weightlessness marked alterations in cardiovascular function and marginal affections of gas exchange can be demonstrated already at rest. They may be considered as contributing factors to orthostatic and exercise intolerance observed after space flight.

Adult↗
PubMed1987

Early (1 to 24h) plasma atrial natriuretic factor changes in the rat during antiorthostatic hypokinetic suspension.

Antiorthostatic hypokinetic suspension (AOH) in rat is currently used as an animal model for simulating weightlessness. This maneuver is responsible for a diuresis, a natriuresis and an increase in central venous pressure (CVP). Knowing the role of CVP in atrial natriuretic factor (ANF) secretion, the aim of the study was to examine the early plasma ANF changes during AOH (angle 30-35 degrees) using Morey's model (tail suspension). The rats were divided into 4 groups: 24 population cage (PC), 24 isolated in separate cages (I), 24 were attached by the tail (Morey's model) and remained in the horizontal position (attached horizontal: AH). At the end of this period of 7 d, 12 AH were suspended for 1, 2, 6 and 24 h (AOH) and sacrificed with the controls for plasma ANF determination. Our results show that the level of ANF is significantly (p less than .05) higher in AOH rats after 2 h of suspension (16.6 +/- 2 pg/ml vs 10.9 +/- 1.5). A significant increase is also observed between AOH and AH after 2h of suspension (p less than 0.05). Six hours after suspension ANF presents a sharp decline in AOH and no difference is observed between AOH and AH and I. Morey's tail suspension model seems to be valid for the study of the early hormonal effects of simulated weightlessness for ANF.

Animals↗
PubMed1988

Circulating lactate and FFA during exercise: effect of reduction in plasma volume following exposure to simulated microgravity.

We examined the relationship between changes in plasma volume (PV) following simulated weightlessness and the response of blood lactate (BL) and plasma free fatty acids (FFA) during exercise. Ten healthy men (35-49 yr) performed 15 min of submaximal upright cycle ergoemetry at a workrate of 57% of pre-bed rest (BR) maximal oxygen uptake before and after 10 d of continuous 6 degrees head-down BR. During exercise, oxygen uptake (VO2) was measured to assure equivalent energy expenditure for pre-BR and post-BR workrate. Antecubital venous blood samples were collected at rest and during the last 30 s of exercise and analyzed for concentrations of BL and FFA, and hematocrit. Resting PV was measured pre-BR and post-BR with Evans blue dye and total circulating BL and FFA were calculated as the product of PV and concentrations of BL and FFA, respectively. VO2 and FFA concentration during submaximal exercise were unchanged post-BR. During exercise, post-BR BL concentration of 2.9 mmol . L-1 was slightly greater (p less than 0.05) than pre-BR BL concentration of 2.5 mmol . L-1. However, as a result of a 17% reduction (p less than 0.05) in resting PV, total circulating BL during exercise was unchanged while total circulating FFA was reduced (p less than 0.05) post-BR. We conclude that the concentrations of BL and FFA during exercise following simulated weightlessness can be significantly altered by the reduction in PV.

Adult↗