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At least 1,297 records · Page 72Linked to original sources
PubMed1995

Clinorotation affects soybean seedling morphology.

Although spaceflight does not appear to significantly affect seed germination, it can influence subsequent plant growth. On STS-3 and SL-2, decreased growth (measured as plant length, fresh weight and dry weight) was noted for pine, oat and mung bean. In the CHROMEX-01 and -02 experiments with Haplopappus and in the CHROMEX-03 experiment with Arabidopsis, enhanced root growth was noted in the space-grown plants. In the CHROMEX-04 experiment with wheat, both leaf fresh weight and leaf area were diminished in the space-grown plants but there was no difference in total plant height (CS Brown, HG Levine, and AD Krikorian, unpublished data). These data suggest that microgravity impacts growth by whole plant partitioning of assimilates. The objective of the present study was to determine the influence of clinorotation on the growth and morphology of soybean seedlings grown in the BRIC (Biological Research In Canister) flight hardware. This experiment provided baseline data for a spaceflight experiment (BRIC-03) flown on STS-63 (Feb. 3-11, 1995).

Gravitation↗
PubMed1995

Root-hair response to vector-free gravity: role of Ca2+ ions.

In plants, apical growth is demonstrated by a variety of cells, including root hairs (RH) which are tubular outgrowths of root epidermal cells. They are likely to be involved in uptake of nutrients and water, anchorage of plants, maintenance of contact between roots and soil, and root exudation. Over the last years, it has become clear that calcium is involved in various processes which result in tip growth. Previous studies from our laboratory have demonstrated an increase in calcium level in root cells of pea seedlings grown under conditions of space flight and clinorotation. On the basis of these data, we have suggested that such effects of microgravity and clinorotation might be due to the enhancement of Ca2+ influx into hyaloplasm evidently through Ca2+ channels. In this regard, it was interesting to examine the effects of clinorotation and Ca2+ channel blockers (verapamil and nifedipine) on orientation and structure of growing RH that might be an appropriate model system being sensitive to calcium for studying the gravitational effects at cellular level.

Calcium↗
PubMed1995

Future research directions in seeking countermeasures to weightlessness.

The goal of this paper is to briefly review the state of knowledge concerning the adaptive properties of mammalian skeletal muscle in response to varying duration in weightlessness, to identify voids in the understanding of this adaptive process, and to provide some insight for undertaking future research on this important topic.

Animals↗
PubMed1984

Cardiovascular and hormonal (aldosterone) responses in a rat model which mimics responses to weightlessness.

Cardiovascular responses and fluid/electrolyte shifts seen during spaceflight have been attributed to cephalad redistribution of vascular fluid. The antiorthostatic (AO) rat (suspended, head-down tilt of 15-20 degrees) is used to model these responses. This study documents that elevated blood pressures in AO rats are sustained for periods of up to seven days, compared with presuspension values. Increased blood pressures in AO rats suggests a specific response to AO positioning, potentially relatable to a cephalad fluid shift. To assess a role for hormonal regulation of sodium excretion, serum aldosterone levels were measured. Circulating aldosterone concentrations were seen to increase approximately 100% during seven days of AO suspension concurrently with a pronounced natriuresis. These results suggest that aldosterone many not be involved in the long term regulation of increased Na+ excretion in AO animals. These studies continue to show the usefulness of models for the development of animal protocols for space flight.

Adaptation, Physiological↗
PubMed1984

Effects of clinostat rotation on mouse meiotic maturation in vitro.

The effects of microgravity on meiosis, fertilization, and early embryonic development in mammals are being examined by using a clinostat to reorient the cells with respect to the gravity vector. A clinostat capable of supporting mammalian cells in tissue culture has been developed. Initial studies have focused on examining the effects of clinostat rotation on meiotic maturation in mouse oocytes. Oocytes recovered from ovarian follicles were subjected to clinostat rotation on a horizontal or vertical axis or to static conditions for a 16 hr period. No gross morphological changes and no effects on germinal vesicle breakdown were observed under any rotation conditions (1/4, 1, 10, 30, 100 RPM). Success of meiotic progression to Metaphase II was comparable among experimental and control groups except at 100 RPM, where a slight inhibition was observed.

Animals↗
PubMed1995

Review of spaceflight and hindlimb suspension unloading induced sarcomere damage and repair.

Hindlimb suspension unloading (HSU) and spaceflight microgravity induce atrophy of the slow adductor longus muscle fibers which, following reloading, exhibit eccentric contraction (EC)-like lesions (abnormal widening of sarcomeres with A band disruption and excessively wavy, extracted Z lines). These lesions are similar morphologically to those produced in normal muscles after strenuous eccentric exercise. It appears that atrophic muscles exhibit increased susceptibility to eccentric damage because lesions are produced during nonstressful voluntary movements upon return to weightbearing. The EC-like lesions are absent in the unweighted conditions, but appear in HSU rats 15-60 minutes after reloading and in space-flown rates about 4 hrs after landing. By 12 hours, many EC-like lesioned sarcomeres are fully covered by longitudinal patches of Z line-like material which increases in density by 48 hours, producing the so-called "Z line streaming" morphology. In this case, Z line streaming is indicative of rapid repair of damaged sarcomeres rather than the onset of sarcomere breakdown. Immunoelectron microscopy is necessary to determine the composition of this dense material. By 9 days of reloading at 1 gravity, sarcomeres have regained normal structure, except for very rare persistence of faint Z patches. The morphological data indicate that Z patches serve at least two functions: 1) to permit contractile force to be transmitted across the damaged sarcomeres and 2) to provide a scaffold upon which sarcomeres are reconstructed in an active functional muscle.

Animals↗
PubMed1996

Gravity related features of plant growth behavior studied with rotating machines.

Research in plant physiology consists mostly of studies on plant growth because almost everything a plant does is done by growing. Most aspects of plant growth are strongly influenced by the earth's gravity vector. Research on those phenomena address scientific questions specifically about how plants use gravity to guide their growth processes.

Centrifugation↗
PubMed1997

[Preliminary study on differentiation of syndromes during HDT -6 degrees bed rest with traditional chinese medicine].

Differentiation of syndromes during 21 d HDT -6 degrees bed rest was made in 15 healthy young men. The results indicated that the subjects showed mainly deficiency of kidney-Yin, deficiency of Yin and hyperactivity of Yang, insufficiency of spleen-Qi and blood stasis in various degrees during the bed rest. The syndromes were most serious on the 3rd day, and then deficiency of kidney and deficiency of Yin and hyperactivity of Yang became mild gradually but insufficiency of spleen-Qi and blood stasis remained the same. The pulse condition was normal through the bed rest period

Bed Rest↗
PubMed1996

Changes in spectra of heart rate and blood pressure variabilities during bed rest and head-up tilt after bed rest.

Changes in the spectra of heart rate and systolic blood pressure variabilities (HRV and SBPV) were recorded during head-down bed rest and head-up tilt (HUT) in 15 healthy young men. After bed rest, five subjects failed to complete HUT test. During bed rest, the low-frequency (LF) and high-frequency (HF) powers of HRV and SBPV spectra were all significantly decreased, the ratio of low-frequency to high-frequency power of HRV spectrum (LF:HFHRV) increased on the 16th day. During the first 6min of HUT after bed rest, the heart rate was faster, but the LF:HFHRV and the LF power of SBPV spectrum in all subjects were similar to the data during HUT before bed rest. The diastolic and mean arterial pressure were significantly increased during HUT except in those who failed to complete the HUT test after bed rest. The results suggest that the peripheral vascular sympathetic activity and the cardiac parasympathetic activity are decreased with a relative increase in the cardiac sympathetic activity during bed rest, but the cardiovascular autonomic responsiveness during HUT after bed rest is basically preserved.

Adult↗
PubMed1995

Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?

Experiments were undertaken to determine if the reciprocity rule is valid for gravitropic responses of oat coleoptiles in the acceleration region below 1 g. The rule predicts that the gravitropic response should be proportional to the product of the applied acceleration and the stimulation time. Seedlings were cultivated on 1 g centrifuges and transferred to test centrifuges to apply a transverse g-stimulation. Since responses occurred in microgravity, the uncertainties about the validity of clinostat simulation of weightlessness was avoided. Plants at two stages of coleoptile development were tested. Plant responses were obtained using time-lapse video recordings that were analyzed after the flight. Stimulus intensities and durations were varied and ranged from 0.1 to 1.0 g and from 2 to 130 min, respectively. For threshold g-doses the reciprocity rule was obeyed. The threshold dose was of the order of 55 g s and 120 g s, respectively, for two groups of plants investigated. Reciprocity was studied also at bending responses which are from just above the detectable level to about 10 degrees. The validity of the rule could not be confirmed for higher g-doses, chiefly because the data were more variable. It was investigated whether the uniformity of the overall response data increased when the gravitropic dose was defined as (gm x t) with m-values different from unity. This was not the case and the reciprocity concept is, therefore, valid also in the hypogravity region. The concept of gravitropic dose, the product of the transverse acceleration and the stimulation time, is also well-defined in the acceleration region studied. With the same hardware, tests were done on earth where responses occurred on clinostats. The results did not contradict the reciprocity rule but scatter in the data was large.

Acceleration↗
PubMed1997

Spaceflight and the skeleton: lessons for the earthbound.

Loss of bone during extended space flight has long been a concern that could limit the ability of humans to explore the universe. Surprisingly the available data do not support the concept that weightlessness leads inexorably to a depleted skeleton unable to withstand the stress of a return to a 1g environment. Nevertheless, some bone loss does occur especially in those bones most stressed by gravity prior to flight, providing confirmation of the proposal formulated over a century ago by Julius Wolff that mechanical stress determines the form and function of bone. Although the phenomenon of bone loss with skeletal unloading, whether by space flight or immobilization or just taking a load off your feet (literally) is well established, the mechanisms by which bone senses load and adjusts to it are not so clear. What actually is the stimulus and what are the sensors? What are the target cells? How do the sensors communicate the message into the cells, and by what pathways do the cells respond? What is the role of endocrine factors versus paracrine or autocrine factors in mediating or modulating the response? None of these questions has been answered with certainty, but as will become apparent in this review, we have some clues directing us to the answers. Although the focus of this review concerns space flight, it seems highly likely that the mechanisms mediating the transmission of mechanical load to changes in bone formation and resorption apply equally well to all forms of disuse osteoporosis, and are likely to be the same mechanisms affected by other etiologies of osteoporosis.

Animals↗
PubMed1996

Spectral characteristics of heart rate and blood pressure variabilities during head-out water immersion.

To elucidate the roles of the autonomic nervous system in cardiovascular adaptation to microgravity, spectral analysis of heart rate and blood pressure variabilities were conducted during thermoneutral head-out water immersion in 8 healthy young subjects aged 23 to 31 years. In all subjects immersed up to the shoulder, the low-frequency (LF: 0.04-0.15 Hz) component in blood pressure variability and the ratio of LF power to high-frequency power (LF/HF ratio) in heart rate variability decreased, while the high-frequency (HF: 0.15-0.5 Hz) component of heart rate variability increased. Concomitantly, a decrease in heart rate was observed without significant changes in blood pressure during immersion. These results suggest that cardiac and vasomotor sympathetic nerve activities are suppressed and cardiac parasympathetic (vagal) nerve activity is activated during head-out water immersion.

Adult↗