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PubMed1995

Changes of contractile properties of extensor digitorum longus in response to creatine-analogue administration and/or hindlimb suspension in rats.

Changes of contractile properties of extensor digitorum longus in response to hindlimb suspension and/or altered high-energy phosphate contents were studied in rats. A reduction of high-energy phosphates, especially phosphocreatine, was seen in rats fed creatine analogue beta-guanidinopropionic acid (beta-GPA), but they were elevated after 10-d supplementation of creatine. The one-half relaxation time was increased by feeding beta-GPA, but was normalized by creatine supply. The fatigue resistance of creatine-depleted muscle was significantly improved, but tended to decrease by suspension and creatine supply, although it was still better than that in the control diet group. It is indicated that the contractile properties of muscle are influenced by the high-energy phosphate content. It is also suggested that the endurance capacity may be influenced by the mitochondrial respiratory capacity, but not necessarily by the levels of high-energy phosphates.

Animals↗
PubMed1998

Does electrical stimulation of the sciatic nerve prevent suspension-induced changes in rat hindlimb bones?

Osteoporosis due to mineral loss is a major health problem resulting from long-term spaceflight. The development of a suitable countermeasure is essential because an advanced decrease in bone density could be irreversible. Therefore the current study was performed to test our hypothesis that the loading of bones by electrical stimulation-induced muscle contraction may prevent the mineral loss caused by gravitational unloading and bone growth will be maintained. During 10 d of hindlimb suspension, electrical stimulation at 1, 50, or 100 Hz was administered through the left sciatic nerve at the gluteal region of rats with approximately 300 g body weight. The dry weight, mineral content, and mineral density in hindlimb bones were analyzed. The dry weight and mineral content of femur and tibia-fibula in hindlimb-suspended rats tended to be less than in the age-matched cage controls. However, these detrimental effects were prevented by stimulation at 50 and 100 Hz. A positive effect of stimulation was seen even in the nonstimulated limb, although greater effect was induced in the stimulated limb. It is suggested that loading by stimulation-induced muscle contraction at higher frequencies is beneficial for the maintenance of bone growth or the prevention of mineral loss, or both, during hindlimb suspension in rats.

Animals↗
PubMed2000

Neuromuscular adaptation to microgravity environment.

Morphological and/or functional char-acteristics of skeletal muscles have a greater adaptability in response to changes in environmental stimuli. For example, an atrophy associated with a shift of fiber characteristics toward fast-twitch type is a common adaptation of antigravity muscle to a microgravity environment. Neuromuscular responses and possible mechanisms of both neural and muscular adaptations to a microgravity environment are discussed in this article. Responses of morphological, metabolic, and contractile properties, as well as fiber phenotype, of muscles are briefly reviewed. Discussion is further extended to the patterns of electromyogram and tension development of muscle, responses of postural stability and locomotion, and/or motoneurons in order to study the mechanism for muscular adaptation to microgravity.

Adaptation, Physiological↗
PubMed2003

Relationship between transmural pressure and aortic diameter during free drop-induced microgravity in anesthetized rats.

To test the hypothesis that the aortic wall is stretched without increasing aortic pressure (AP) during microgravity (microG), the AP, intrathoracic pressure (ITP), and aortic diameter (AD) were measured in anesthetized Sprague-Dawley rats during 4.5 s of microG produced by freefall. A smooth and immediate reduction in gravity (G) occurred during freefall, microG being achieved 100 ms after the start of the drop. Acute microG elicited an immediate increase in AD, which was not accompanied by an increase in AP. However, the ITP decreased during microG resulted in an increase in the calculated transmural pressure (TP = AP-ITP) of the aortic wall. A simple linear regression analysis showed that the slopes of the plot of AP vs. AD differed at 1 G and microG, whereas those for the plot of TP vs. AD did not. Thus, the increase in AD during microG was accounted for by the increase in TP. These results suggest that a decrease in ITP, resulting in an increase in TP of the aorta, is a key issue in understanding cardiovascular responses to microG.

Anesthesia↗
PubMed2006

Oxygen uptake kinetics following 20 days of unilateral lower limb suspension.

The purpose of the present study was to examine the effect of unilateral lower limb suspension (ULLS) deconditioning on oxygen uptake kinetics. Eight healthy males underwent ULLS for 20 days and performed a series of 6-min square-wave transitions from rest to 60-W single-leg cycling exercises just before and after ULLS. To characterize the kinetics of the oxygen uptake response, a single exponential model was applied to the data until the end of the fast component omitted the first 15 s of the on-transit using a nonlinear least-squares fitting procedure. The following results were found: (i) the time constant of oxygen uptake was unchanged before and after ULLS; (ii) although there was no significant difference in the baseline and the asymptotic amplitude of the fast component, the asymptote, i.e., the absolute asymptotic amplitude of the fast component (the sum of the baseline and the asymptotic amplitude), and the end exercise oxygen uptake were decreased after ULLS; (iii) the contribution of the slow component to the total response of oxygen uptake was unchanged at pre- and post-ULLS. In conclusion, the asymptote in the fast component and the end exercise oxygen uptake were decreased after 20-d ULLS, though the response speed and the amplitude of the slow component of oxygen uptake were not changed. It is suggested that deconditioning as a result of limb disuse affects oxygen uptake response.

Adaptation, Physiological↗
PubMed1996

Postural control under clinorotation in upside-down catfish, Synodontis nigriventris.

The upside-down catfish Synodontis nigriventris has a unique habit of swimming and resting upside-down in free water. This behavior leads to the assumption that the catfish has a specific gravity information processing system. We examined the postural control behaviors in the catfish under clinorotation which is usually used for producing pseudo-microgravity. Synodontis nigriventris kept its body posture at a stable area of the rotated flask in which the catfish was kept, when it was clinorotated at the rate of 60 rpm. In contrast to Synodontis nigriventris, a related species, Corydoras paleatus, did not show such steady postural control. When the flask was rotated at a lower rate of 30 rpm or a higher rate of 100 rpm, Synodontis nigriventris as well as Corydoras paleatus showed a considerable disturbed control of body posture. In this condition, they were frequently rotated with the flask. These findings suggest that Synodontis nigriventris has a high ability to keep upside-down posture and the gravity sensation in this catfish is likely to contribute to its different postural control from that of many other fishes.

Animals↗
PubMed2000

STS-95 space experiment for plant growth and development, and auxin polar transport.

The principal objective of the space experiment, BRIC-AUX on STS-95, was the integrated analysis of the growth and development of etiolated pea and maize seedlings in space, and the effect of microgravity conditions in space on auxin polar transport in the segments. Microgravity conditions in space strongly affected the growth and development of etiolated pea and maize seedlings. Etiolated pea and maize seedlings were leaned and curved during space flight, respectively. Finally the growth inhibition of these seedlings was also observed. Roots of some pea seedlings grew toward the aerial space of Plant Growth Chamber. Extensibilities of cell walls of the third internode of etiolated pea epicotyls and the top region of etiolated maize coleoptiles which were germinated and grown under microgravity conditions in space were significantly low. Activities of auxin polar transport in the second internode segments of etiolated pea seedlings and coleoptile segments of etiolated maize seedlings were significantly inhibited and extremely promoted, respectively, under microgravity conditions in space. These results strongly suggest that auxin polar transport as well as the growth and development of plants is controlled under gravity on the earth.

Biological Transport↗
PubMed2003

Reduced allelopathic inhibition of lettuce (Lactuca sativa) growth caused by velvet bean (Mucuna pruriens) under 3D-clinorotation.

Allelopathy between Mucuna pruriens (velvet bean) and Lactuca sativa (lettuce) was studied under 3D-clinorotation. Growth of both roots and shoots of lettuce seedlings was suppressed by the presence of velvet bean. The degree of suppression was less on the clinostat compared to the normal static earth gravity. L-DOPA (L-3, 4-dihydroxyphenylalanine) is known to be a major substance in allelopathy of velvet bean. Amount of L-DOPA diffused out from a sintered filter paper into agar medium was compared between clinorotation and control group, and found no significant difference. It was concluded that some factors related to release, transport, and sensing phenomena of allelopathic substances may be responsible to the new findings in this study.

Biological Transport↗
PubMed2003

Growth of endophyte, Neotyphodium, and its host plant, tall fescue (Festuca arundinacea), under 3D-clinorotation.

Growth of a filamentous fungus endophyte, Neotyphodium, and its host plant, tall fescue, Festuca arundinacea, was examined during the seed germination process under pseudo-microgravity [correction of micrgravity] generated by three dimensional (3D-) clinorotation. The shoot growth of tall fescue infected with the endophyte was remarkably suppressed on a 3D-clinostat compared with that of the ground control. Without being infected, shoot growth of tall fescue was not strongly affected by the 3D-clinorotation. Many aggregated hyphae were observed in the plant seed incubated for 1-day on the 3D-clinostat [correction of clinost] than in those kept on the ground. These results indicate that the clinorotation induces responses in the endophyte and its host plant different from those under normal gravity.

Festuca↗
PubMed2005

Interventions to prevent bone loss in astronauts during space flight.

This paper reviews the interventions to stabilize calcium balance and bone metabolism and prevent bone loss in astronauts during space flight. Weightlessness during space flight results in calcium, vitamin D, and vitamin K deficiency, increases urinary calcium excretion, decreases intestinal calcium absorption, and increases serum calcium level, with decreased levels of serum parathyroid hormone and calcitriol. Bone resorption is increased, whereas bone formation is decreased. The loss of bone mineral density (BMD) in the spine, femoral neck and trochanter, and pelvis is 1.0-1.6% per month. High calcium intake and vitamin D supplementation during space flight does not affect bone metabolism, but prevents an elevation of serum calcium level through increased calcitriol level, while vitamin K counteracts the reduction in bone formation. However, there are no data to show the efficacy of pharmaceutical agents for prevention of development of osteoporosis in astronauts during flight, although the preventative effect of bisphosphonates, testosterone, and vitamin K2 on cancellous bone loss in the tibia or BMD loss in the hindlimb was reported in tail-suspended mature rats. It still remains uncertain whether these agents can prevent cortical bone loss caused by weightlessness in tail-suspended rats. Therefore, in addition to calcium, vitamin D, and vitamin K supplementation, agents that have both potent anti-resorptive and anabolic effects on cancellous and cortical bone may be needed to stabilize calcium balance and bone metabolism and prevent bone loss in astronauts during space flight.

Aerospace Medicine↗
PubMed2001

Human characteristics of pair assembly work in a microgravity environment.

This research focuses on analyzing the human characteristics of pair assembly work in a microgravity environment. To obtain the necessary data, two groups of test subjects participated in an experiment in a pseudomicrogravity environment, and how such factors as work allotment, sizes of assembled objects, and conditions of parts influence the work efficiency were studied. The results show when the assembled object is smaller that it is easier to change the object's position and that workers can move it to an appropriate site and work easily. If the assembly object is attached to an object with very large mass, the work allotment does not result in a difference in work time. As for positioning the objects, step-saving processes can shorten the work time. For instance, if a part can be put so that both ends automatically touch the proper spots, time can be shortened.

Cooperative Behavior↗
PubMed1991

Effect of water immersion on post-rotatory and caloric nystagmus.

Caloric nystagmus and post-rotatory nystagmus were recorded with and without head-out water immersion. As water immersion reduces body weight by about 90% owing to buoyancy, it decreases somatosensory inputs. Thus water immersion can be used to simulate a weightless environment. Caloric nystagmus was enhanced significantly by water immersion; however, post-rotatory nystagmus was not. These findings demonstrate that caloric nystagmus is easily affected by water immersion which decreases somatosensory inputs, but that post-rotatory nystagmus is not.

Caloric Tests↗
PubMed2002

Effect of different dietary protein composition on skeletal muscle atrophy by suspension hypokinesia/hypodynamia in rats.

Under microgravity conditions similar to those in space, it is known that various nutritional and physiological changes in the body are induced. Especially in the aspect of nutrition, muscle atrophy is a characteristic phenomenon accompanying weightlessness. This study was conducted to investigate the ameliorated effect of muscle atrophy caused by suspension hypokinesia by using the soy protein isolate (SPI) as the protein source in comparison with casein. Male Wistar strain rats (8 wk old) were divided into two groups, each suspended with a suspension harness, and fed on a 20% SPI diet or a 20% casein diet for 10 d. The body weights of the suspended rats fed casein or SPI decreased similarly. The weight of the gastrocnemius and soleus muscle were decreased by suspension hypokinesia; however, the degree of the decrease of the muscle weights, especially soleus muscles, of rats fed the SPI diet was smaller than that of rats fed the casein diet. Serum Ntau-methylhistidine concentration was significantly lower in rats fed the SPI diet than in rats fed the casein diet. Similarly, the activities of muscle protein-degrading enzymes such as calpain and proteasome were significantly lower in rats fed the SPI diet than in rats fed the casein diet. Cathepsin B+L activities were not affected by the SPI or the casein diet. Therefore it is suggested that SPI caused a reduction of the proteolysis of myofibrillar protein in skeletal muscles through a reduction of calpain and proteasome activities, in consequence to ameliorate the muscle atrophy.

Animals↗
PubMed1999

[Space medicine].

Explore the source record for details and available documents.

Aerospace Medicine↗
PubMed1999

[The effect of support loads and CNS stimulants on the development of the atrophic process in the muscles of suspended rats].

The histomorphometric method there was used to study effects of ephedrine, strychnine, and support loads on the atrophy of m. soleus and m. gastrocnemius in rats with load-deprived lower extremities (14-day tail-suspension). Deficiency of support loads on the lower extremities led to atrophy of the muscles, especially the slow m. soleus. Injections of ephedrine (0.06 mg/kg), strychnine (0.015 mg/kg) as well as ephedrine and strychnine at one and the same time did not affect the development of atrophy. On the contrary, daily 2-hr support loading of the rear extremities had a favourable effect on the muscle atrophy as it was slowed down. Particularly effective were injections of ephedrine on the background of support loads following which the mass of m. soleus in the suspended rats was close to vivarium control. It is suggested that the preventive effect of ephedrine is associated with stimulating the CNS controllers of the somatotropic function of the pituitary body and eventual enhancement of the somatotropic hormone production.

Animals↗
PubMed1999

[The development of the syndrome of congestive parenchymatous organs under conditions of short-term hypokinesia].

Five series of head-down (-10 degrees to -30 degrees, up to 18 hr) tilt tests were performed with participation of 65 healthy male subjects. The ultrasonic technique was used to investigate the liver, spleen, pancreas, kidney, and the main abdominal vessels, i.e. aorta in the abdomen and superior mesenteric artery, interior caval, portal, and splenic veins. A few hours of HDT already brought about a complex of load-deprivation reflexes (the syndrome of stagnant parenchymal organs) characterized by a prolonged venous congestion in the abdominal organs-vessels system, increases in sizes and blood filling of the liver, spleen, pancreas, kidney, and the main arteries and veins in this hemodynamic region. This was the first time when increases in pancreas including its head, body and tail, and the abdominal blood vessels were quantified at the beginning of adaptation to HDT. The load-deprivation reflexes arising in this period were hemodynamic by nature. Considering the significant functional strain of the abdominal organs and vessels and particularly the limited control of excessive blood flow towards the pancreas and kidneys, there is a good reason to look into the ways to improve the existing countermeasures against the consequences of immobilization for humans both in general clinic and preventive medicine, and in short- and long-term space missions.

Abdomen↗
PubMed1999

[Errors in pointing under various body orientation relative to the gravity vector].

Errors in pointing to remembered target locations were measured in healthy subjects in upright, supine and prone positions, i.e. in three positions differing in body and arm movement orientation relative to the gravity vector. The X-error was unaffected by the body position, whereas the Y-error was dependent on subject's orientation relative to the gravity vector. In two lying positions, the subjects pointed below and in the vertical posture above the remembered target locations. On the contrary, the variable error was differentially affected by orientation of the movement trajectory relative to the gravity vector. In the supine position, the variable error was larger and in the prone position, smaller than in the upright posture. The gravity bias in pointing errors suggests that the motor program generated in the lying position is not modified to adapt to altered orientation relative to the gravity vector.

Adult↗