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PubMed2004

Counteracting effect of head-up tilt on increased femoral venous compliance after simulated weightlessness in rabbits.

BACKGROUND: The increased femoral venous compliance is one of the factors of orthostatic intolerance after space flight. The purpose of this study was to observe the effect of daily head-up tilt (HUT) on stress-strain relationship of femoral vein during simulated weightlessness in rabbits. METHODS: Head-down tilt (HDT) 20 degrees rabbit model was used to simulate weightlessness. Twenty-four healthy male New-Zealand rabbits were randomly divided into three groups: simultaneous control, 21 d HDT, and 21 d HDT plus daily 2 h HUT 45 degrees, with 8 in each. Twenty-one days later, stress-strain relationship of femoral vein was examined. RESULTS: Under the same stress, the circumferential strain both in the 21 d HDT group and the 21 d HDT plus daily 2 h HUT group increased significantly than those in the control group. There were no significant differences between these two groups. There were no significant changes in the longitudinal strain among three groups under the same stress. CONCLUSIONS: The femoral venous compliance of rabbits increase significantly after 21 days simulated weightlessness. Daily 2 h HUT 45 degrees could not prevent increase of femoral venous compliance in rabbits induced by 21 days simulated weightlessness.

Adaptation, Physiological↗
PubMed1998

Effects of simulated weightlessness and gamma-irradiation on myocardial cells and osteoblasts.

The effects of simulated weightlessness and gamma-irradiation on the structure and function of the myocardial cells and osteoblasts were investigated with a rotating clinostat and 2 Gy 60Co gamma-irradiation. The results showed: (1) Under the simulated weightlessness (SWL), the diameter of the myocardial cells decreased 40%. And the long-short diameter proportion decreased 70%, (P < 0.01); SWL affected the cell skeleton and the distribution of microfilament became ununiform, the orientation was unclear; SWL had significant effects on osteoblast disintegration and proliferation. The disintegration function decreased and the proliferation process was inhibited; (2) 2 Gy 60Co gamma-ray irradiation had significant effects on Lactate Dehydrogenase (LDH) activity and Superoxide Dismutase (SOD), Malonaldehyde (MDA) content in the myocardial cells, (P < 0.05) (5) A synergistic effect was observed between irradiation and SWL.

Animals↗
PubMed2001

[Changes of early components of auditory ERPs during HDT-simulated weightlessness].

Objective. To study changes of early components of the auditory ERPs during simulated weightlessness. Method. The event-related potentials (ERPs) during an auditory location discrimination were compared between head down tilt (HDT) and head up tilt (HUT) conditions in 14 normal subjects. Result. The early components of T-ERPs and NT-ERPs decreased significantly during HDT as compared with that during HUT. The reduction of mean potential amplitude during HDT was more marked at left-forehead area (F5). Conclusion. These data provided further evidence showing that the early activity process of brain was also affected by simulated weightlessness.

Adult↗
PubMed2000

[Effects of simulated weightlessness on carbohydrate intake and serum lipids].

OBJECTIVE: To observe the effects of simulated weightlessness on the nutritional state and contents of serum lipids in human. METHOD: Eighteen healthy men were exposed to 21 d bed rest with -6 degrees head down tilt (HDT -6 degrees). Nutrients intake was calculated and the lipids levels were determined on the first, eleventh and twenty-first day. RESULT: Intake of the three main nutrients, carbohydrates, protein and fat met the physiological requirement essentially, but carbohydrates intake was significantly reduced in the second week. There were no significant differences among the lipid levels during different periods. CONCLUSION: Simulated weightlessness may exert a short-term and reversible influence on human nutritional intake except for lipids.

Adolescent↗
PubMed2001

[Changes of brain potentials related to auditory location discrimination during simulated weightlessness].

Objective. To study changes of brain response in distinguishing auditory location during simulated weightlessness. Method. The event-related potentials (ERPs) during auditory location discrimination were compared between head down tilt (HDT) and head up tilt (HUT) conditions among 14 healthy subjects. Result. (1) Both the target (T) and non-target (NT) auditory signals induced significant ERPS; (2) The slow potential was significantly lower for both T and NT-ERPs during HDT as compared with that during HUT; (3) The reduction of mean slow potential amplitude during HDT was more significant for the target signals from right-rear position and lightest for the target signals from right-front position. This phenomenon was more remarkable at left-front area. Conclusion. These data provide further evidence that the higher brain function was affected by simulated weightlessness.

Aerospace Medicine↗
PubMed2003

Effects of simulated weightlessness on myosin heavy chain expression of soleus intrafusal muscle fibers in rats.

OBJECTIVE: To examine the myosin heavy chain expression in intrafusal fibers in rat soleus muscle before and after simulated weightlessness and to analyse the mechanism involved in muscle spindle deterioration during simulated weightlessness. METHOD: The rats were divided into 3 groups: 7 d, 14 d tail-suspension group and control group. Control and experimental spindles were examined using monoclonal antibodies specific for myosin heavy chains of slow-tonic (ALD58) and fast-twitch (MF30) chicken muscles by the immunoperoxidase reaction utilizing the ABC (avidin-biotin-complex) method. RESULT: The extrafusal muscle fibers did not exhibit immunoreactivity to ALD58 and MF30. Only intrafusal fibers bound these antibodies. The bag 1 fiber and bag 2 fiber reacted to ALD58. The bag 2 fiber and chain fibers stained with MF30. After 7 d suspension the immunoreactivity of the bag 1 fiber and bag 2 fiber to ALD58 decreased, while the immunoreactivity of the bag 2 fiber and chain fibers to MF30 increased. After 14 d suspension the immunoreactivity of the bag 1 fiber and bag 2 fiber to ALD58 decreased remarkably, even disappeared. While all of the intrafusal fibers reacted to MF30 and the immunoreactivity increased obviously. CONCLUSION: The expression level and patterns of MHC in intrafusal fibers of rat soleus muscle changed after simulated weightlessness.

Animals↗
PubMed2005

[Changes in voltage-dependent calcium channel currents of vascular smooth muscle cells isolated from small mesenteric arteries of simulated weightless rats].

The aim of the present study was to examine the changes in the function of voltage-dependent calcium channels (VDC) of vascular smooth muscle cells (VSMCs) isolated from small mesenteric arteries of rats subjected to 1-week or 4-week simulated weightlessness. The whole-cell recording mode was used to record current densities and Ba(2+) was used as charge carrier. Curves and fitting parameters describing steady-state activation and inactivation characteristics of VDC were thus obtained. The inward currents recorded from the VSMCs of small mesenteric arteries were mainly the Ba(2+) currents through the long-lasting type VDC (L-VDC). Compared with that of the control rats, the L-VDC current density of VSMCs from small mesenteric arteries showed a trend toward a decrease in the rats after 1-week , while a significant decrease was observed in the rats after 4-week simulated weightlessness. However, there were no significant differences in the opening and closing rates of L-VDCs, the position of steady-state activation and inactivation curves, and in the parameters, V(0.5) and k, between either of the two groups and its respective control group. The membrane capacitance and the reversal potential of the VSMCs from the small mesenteric arteries of rats after simulated weightlessness also showed no significant changes. These findings suggest that the decreased function of the L-VDC in hindquarter VSMCs might be one of the electrophysiological mechanisms that mediate the depressed vasoreactivity and atrophic change in hindquarter arteries during adaptation to simulated weightlessness in rats.

Animals↗
PubMed2002

Lipid peroxidation in rat brain is increased by simulated weightlessness and decreased by a soy-protein diet.

This study tested whether or not simulated weightlessness by tail-suspension increases the levels of lipid peroxidation products in rat brain. The brain tissues of rats on a soybean diet were also assayed for lipid peroxidation products to evaluate the possible role of soy-protein as a dietary anti-oxidant. Male Sprague-Dawley rats were used. Group 1 rats were fed standard Purina rat chow ad libidum and served as controls. Group 2 rats were fed a soybean diet containing 37% soy-protein and were not tail-suspended. Group 3 rats were fed standard Purina rat chow ad libidum and were tail-suspended to induce simulated weightlessness. After 2 wk, all of the rats were killed. Each whole brain was segmented into frontal cortex, cerebellum, and brain stem. After a specific weight of each segment was excised, the residual tissues were combined and used as a whole brain sample. The samples were analyzed for lipid peroxidation products by a chromogenic assay that reacts with malondialdehyde (MDA) and 4-hydroxyalkenals (4-HNE). The mean concentrations of lipid peroxidation products (MDA plus 4-HNE) in whole brain, frontal cortex, cerebellum, and brain stem of the control rats ranged from 16 to 18 micromol/g; the corresponding means ranged from 10 to 13 micromol/g in rats fed the soybean diet, and from 22 to 26 micromol/g in the tail-suspended rats. Thus, the mean levels of lipid peroxidation products in brain tissues were decreased in the rats fed the soy diet and were increased in the rats that were tail-suspended to simulate weightlessness, when compared to those of rats fed a regular diet.

Aldehydes↗
PubMed1983

Fluid shifts and muscle function in humans during acute simulated weightlessness.

Head-down tilt is considered an effective experimental model to simulate weightlessness. To determine the acute effects of simulated weightlessness on transcapillary fluid balance, tissue fluid shifts, muscle function, and triceps surae reflex time, eight supine subjects were tilted 5 degrees head down for 8 h. A cephalic fluid shift from the legs was indicated by facial edema, nasal congestion, increased urine flow, decreased creatinine excretion, reduced calf girth, and decreased lower leg volume. As measured by wick catheters inserted under local anesthesia, interstitial fluid pressure in the tibialis anterior muscle (4.6 +/- 0.6 mmHg) and subcutaneous tissue (0.6 +/- 0.5 mmHg) of the lower leg fell significantly to -2.8 +/- 0.5 and -3.8 +/- 0.4 mmHg, respectively. Other transcapillary pressures (capillary and interstitial fluid colloid osmotic pressures) were relatively unchanged. Needle-biopsy specimens, obtained just before and after tilt, indicated that total water content of soleus muscle was unchanged during 8 h of head-down tilt. After head-down tilt, isometric strength and isokinetic strength of the plantar flexors were unchanged. Triceps surae reflex time associated with plantar flexion movement slowed slightly after the tilt maneuver. Collectively these results demonstrated a dehydration effect of head-down tilt on muscle and subcutaneous tissues of the lower leg that may affect muscle function.

Adult↗
PubMed1996

Cortico-adrenal function under simulated weightlessness during gestation in the rat--effects on fetal development.

To examine the effects of simulated weightlessness on cortico-adrenal function and on fetal development, we suspended pregnant rats for 20 days. The levels of adrenal and plasma corticosterone were examined in mothers and in fetuses. The animal control group was kept single in standard cages. Growth of the suspended animals was repressed for the first 8 days of the experiment, but thereafter it increased greatly, as did the daily food intake. By the 18th day of the experiment, the body masses and food intake of the two groups were equal. No modification in circulating corticosterone was found. It appears that there is no stress in pregnant rats submitted to simulated weightlessness.

Adaptation, Physiological↗
PubMed2002

Effects of simulated weightlessness on bone metabolism in rats at different ages.

OBJECTIVE: To compare the effects of simulated weightlessness on age-related bone metabolism and on the mechanical parameters of the weight-bearing bones of rats at different ages. METHODS: Two-month-old and 6-month-old rats (8 in each group) were both subjected to tail suspension test for up to 4 weeks, with 2 groups of rats of corresponding ages (n=8) serving as control. The bone metabolism markers, biomechanical parameters of the femurs, along with the growth and mineral contents of the tibia, were respectively measured and compared with those of the controls. RESULTS: The bone formation markers, alkaline phosphatase and osteocalcin levels, dropped drastically in both groups of rats undergoing tail suspension test (P<0.01), which also induced significant hypocalcaemia (P<0.01). Bone material loss of the tibia occurred in both groups of rats receiving the test (P<0.01) whose effect on the volume and mass of fresh tibia was age-related (P<0.05), but the degree of mineral loss was not consistent with calcium loss in rats at different ages. Except for elastic deformation (P>0.05), both structural and biomechanical properties altered significantly after tail suspension test (P<0.01), and the changes of maximum deformation and maximum load were related to the age of the rats (P<0.05). CONCLUSION: The result is an age-related difference in the response of bone metabolism to simulated weightlessness.

Animals↗
PubMed2000

[Counteracting effects of intermittent head-up tilt on simulated-weightlessness induced atrophy of anti-gravity muscles].

Objective. To study the efficacy of intermittent + Gz (45 degrees head-up tilt, HUT) exposures in preventing or alleviating atrophic changes in hind limb muscles induced by simulated weightlessness. Method. Male Sprague-Dawley (SD) rats were assigned randomly to one of three groups: simultaneous control (CON), simulated weightlessness (SUS), and SUS plus 6 h/d HUT (SUS + HUT). Muscles examined included soleus (SOL), medial gastrocnemius (correction from grastrocnemius) (MG), lateral gastrocnemius (LG) and extensor digitorum longus (EDL). Sections were treated with an adenosinetriphosphatase (ATPase) stain or alkaline phosphatase stain. The cross-sectional areas (CSA) of fibers, the relative proportion of type I fiber and the ratio of capillaries/fibers (C/F) were measured using Leica image analysis system. Result. Compared with CON, the wet weight of hind limb muscles in SUS were significantly reduced. The changes of wet weight in different groups were various. The C/F ratios of all muscles were significantly reduced. SUS + HUT rats showed significant increases in SOL and MG wet weight, and the relative counter-effects of intermittent HUT were 93.4% and 34.8%, respectively. In SUS + HUT group, the CSA of both type I and II fibers and relative proportion of type I fibers were completely recovered in SOL, and partially recovered in MG, while the counter-effects were much less obvious in the fibers of LG and EDL. However, HUT resulted in a significant recovery of the C/F ratios in all muscles. Conclusion. The present study demonstrated that intermittent HUT is effective in counteracting the atrophy induced by simulated weightlessness. The result that reactivity to HUT varied among different muscles suggests that the intermittent artificial gravity should be complemented with other countermeasures.

Animals↗
PubMed2003

[Effects of "Qiang Gu Kang Wei" compound prescription on bone metabolism in rats under simulated weightlessness].

OBJECTIVE: To investigate the effect of "Qiang Gu Kang Wei" prescription on bone metabolism in simulated weightless rats. METHOD: Male SD rats were randomly divided into five groups: 1) free active control (FAC); 2) tail-suspended control (TS); 3) tail-suspended and treated with large dose of the prescription (TS + L) (30 g/kg); 4) tail-suspended and treated with middle dose of the prescription (TS + M) (20 g/kg); 5) tail suspended and treated with small dose of the prescription (TS + S) (10 g/kg). The experiment lasted 3 weeks. The effect of the prescription on bone biomechanical properties, bone density, bone mineral contents, and bone biochemical markers of bone metabolism were examined. RESULT: Bone biomechanical properties, bone density, total and bound bone gla protein (BGP) of serum all increased significantly in three groups treated with the prescription. CONCLUSION: "Qiang Gu Kang Wei" prescription prevents bone loss, hence maintains bone density and bone biomechanical properties under simulated weightlessness.

Animals↗
PubMed1987

Skeletal response to simulated weightlessness: a comparison of suspension techniques.

The skeletal response to simulated weightlessness was studied in rats subjected to two different methods of suspension. Skeletal unloading of the hind limbs for a two week period was achieved by use of either a back harness or tail traction. In comparison to pair-fed control rats, back-suspended rats failed to gain weight whereas tail-suspended rats exhibited normal weight gain. Quantitative bone histomorphometry revealed marked skeletal abnormalities in the proximal tibial metaphysis of back-suspended rats. Loss of trabecular bone mass in these animals was due to a combination of depressed longitudinal bone growth, decreased bone formation, and increased bone resorption. In contrast, the proximal tibia of tail-suspended rats was relatively normal by these histologic criteria. However, a significant reduction in trabecular bone volume occurred during 2 weeks of tail suspension, possibly due to a transient inhibition of bone formation during the early stages of skeletal unloading. Lack of weight gain in back-suspended rats may be indicative of a pronounced stress response during which corticosteroids adversely affected the skeleton. Maintenance of normal weight gain by tail-suspended rats provides evidence for the less traumatic nature of this method of suspension. Our findings indicate that tail suspension may be a more appropriate model for evaluating the effects of simulated weightlessness on skeletal homeostasis.

Adipose Tissue↗
PubMed2003

[Preliminary (correction of Priliminary) study on effects of "planning treatment according to diagnosis" on physiological changes during simulated weightlessness].

OBJECTIVE: To observe effects of the planning treatment according to diagnosis on body syndromes caused by simulated weightlessness. METHOD: Ten subjects underwent HDT -6 degrees for 14 d were randomly divided into the traditional Chinese Medicine group (ME) and control group (CON). Differentiation of syndromes were made and parameters related to the differentiation syndromes, including plasma cortisone, blood viscosity, red cell deformation, excretion rate of urine xylose, and amount of urine were surveyed simultaneously. RESULT: Both differentiation of syndromes and the physiological parameters in group ME could be maintained at the pre-bed rest levels or changed only slightly. CONCLUSION: The Chinese herb compound had an adjusting effect on deficiency of kidney-Yin, blood stasis, insufficiency of spleen-Qi and changes of related physiological parameters caused by 14 d bed rest simulated weightlessness, among which the effect on deficiency of kidney-yin and blood stasis were more distinct.

Adolescent↗
PubMed1995

Contractile properties of the human triceps surae muscle during simulated weightlessness.

The effect of a 120-day period of bed rest on the mechanical properties of human triceps surae muscle was studied in a group of male volunteers (n = 6, mean age 38 years). The results shows that the contractile properties of skeletal muscle in response to disuse change considerably. Time to isometric peak tension of the triceps surae muscle increased from 120 (SEM 3.0)ms to 136 (SEM 2.9)ms (P < 0.01), half relaxation time from 92 (SEM 2.1)ms to 100 (SEM 1.6)ms (P < 0.05) and total contraction time from 440 (SEM 9.9)ms to 540 (SEM 18.7)ms (P < 0.001). Isometric twitch force (Ft) decreased by a mean of 36.7% (P < 0.05), maximal voluntary contraction (MVC) and maximal force (Fmax) by a mean of 45.5% and 33.7%, respectively (P < 0.05-0.01). The value Fmax:Ft ratio increased by 3.6% (nonsignificant). The difference between Fmax and MVC, expressed as a percentage of Fmax and referred to as force deficiency, has also been calculated. Force deficit increased by a mean of 60% (P < 0.001) after bed rest. Force-velocity properties of the triceps surae muscle calculated according to an absolute scale of voluntary and electrically evoked contraction development decreased considerably. The calculations of the same properties on a relative scale did not differ substantially from the initial physiological state. The results would suggest that muscle disuse is associated with both atrophy and a reduction in contractility in the development of Fmax and decreased central (motor) drive. The change in the triceps surae muscle contractile velocity properties may indicate changes in the kinetically active state in the muscles.

Adult↗
PubMedDate not supplied

Effects of muscle electrostimulation during simulated weightlessness.

In a 45-day experiment test subjects were exposed to bed rest with their heads down at -4 degrees C. Twice a day their muscles of the stomach, back, femur, and shin were stimulated with electric current for 25-30 min. The value of muscle tension was close to their maximum voluntary contraction. The main objective was to prevent muscle atrophy and to maintain their trophic and functional state. Physiological measurements were carried out together with morphological, cytochemical, and biometric evaluations. The tissue removed during biopsy from M. soleus 7 days before the test and on the 30th hypokinetic day was used as substrate. Electrostimulation affected favourably the tone and strength of muscles as well as their static and dynamic endurance. Morphological studies showed a positive effect of electrostimulation on the muscle tissue, preventing the development of atrophic processes. During the first post-hypokinetic day orthostatic tolerance increased.

Bed Rest↗