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At least 397 records · Page 22Linked to original sources
PubMed2003

Composition and digestive tract retention time of ruminal particles with functional specific gravity greater or less than 1.02.

The objective of this study was to determine composition, particle size distribution, and in vivo kinetics of ruminal particles having functional specific gravity (FSG) greater or less than FSG of particles found in the omasum and reticulum of lactating dairy cows. Particles from the reticulum and the omasal had FSG of 1.03 and 1.02, respectively. Particles from ruminal contents with FSG higher (HP) or lower (LP) than 1.02 were isolated and labeled with Er or Dy, respectively. Four ruminally cannulated, lactating Ayrshire dairy cows were fed all-grass silage (AS) or 54% grass silage:46% concentrate (SC) diets in a cross-over design trial and used to study chemical composition and ruminal and total tract kinetics of HP and LP. Labeled particles were pulse dosed into the rumen of the cows and disappearance of the markers from ruminal HP and LP pools and excretion in feces was monitored for 72 and 120 h, respectively. Fecal marker excretion data were fitted using two-compartment mathematical age-dependent/age-independent (Gn-->G1) models. Inclusion of concentrate in the diet (SC) increased (P < 0.05) apparent total tract digestibility of dietary DM, OM and N. Digestibility of fiber fractions, NDF and ADF, was lower (P < 0.01 and P < 0.05, respectively) for SC compared with AS. The heavy particles had higher (P < 0.01) indigestible NDF and lower (P < 0.01) N concentration than LP. Particles from the HP pool passed from the rumen more rapidly (P < 0.01) than particles from LP (0.044 and 0.019 h(-1), respectively). Diet had no effect on particle rate of disappearance or pool size in the rumen. Across diets, pool size of LP was consistently larger (P < 0.05) than that of HP. Diet had no effect on total tract mean retention time (MRT) of LP or HP. Total tract MRT of LP was greater (P < 0.05) than MRT of HP (59.6 vs. 49.0 h, respectively). Results from this study support the hypothesis that functional specific gravity is an important factor determining the rate of outflow and residence time of feed particles within the reticulo-rumen and total digestive tract. Our data indicate that digesta particles with functional specific gravity greater or less than 1.02 have different composition and flow characteristics. Heavier particles contain more indigestible fiber and less N and are likely depleted of substrate available for microbial fermentation, are smaller in size, and have a higher passage rate/shorter retention time in the digestive tract than lighter particles.

Animal Feed↗
PubMed1975

The effect of light and specific gravity on embryo weight and embryonic mortality.

Eggs from Single Comb White Leghorn chickens were divided into two approximately equal groups with the range of specific gravities being present in each group. One group was incubated in a darkened Humidaire Hatchett while the other was incubated in an identical machine equipped with two 20 Watt fluorescent tubes which produced 8.3 X 10(3) ergs/cm.2-sec. at the surface of the eggs. The recommended temperature and humidity settings were used in both machines. After 7 days of incubation embryos from the lighted incubator were significantly (P less than .01) larger than those incubated in the dark. There were significantly more live embryos from low and high specific gravity eggs in the light than in the dark. There was no difference in embryonic mortality between groups for the eggs with intermediate specific gravities. Embryos from White Leghorn eggs incubated in the presence of light were significantly (P less than .01) larger on each day of incubation from day 2 through hatch. Eggs incubated in the lighted incubator hatched at 18 and 19 days and produced larger chicks than those hatched at 20 and 21 days in the dark.

Animals↗
PubMedDate not supplied

[Ultrastructure of the neuromuscular junctions in the rat soleus muscle under varying gravity conditions].

Changes in the ultrastructure of neuromuscular junctions have been considered as an index to adaptation of Wistar rats (whose pre- and postnatal ontogenesis proceeded on a centrifuge under constant rotation until the age of two months) to the hypergravity conditions (2G) and, then, to earth gravity (1G): on the 2nd and 15th days after centrifuge stoppage. The dynamic of synaptic vesicles was shown: their number increased at 2G and gradually decreased at 1G. Local damage of muscle fibers, partial separation of the motor axonal terminal from intrafusal fiber, and membrane twisting were noted at the increased gravity-dependent static load (2G). Neuromuscular junctions with signs of remodeling occurred more frequently in the experimental rats than in the control ones. It was proposed that adaptation of rats to 1G gravity after a prolonged sojourn under the hypergravity conditions (2G) was not completed within the studied period.

Animals↗
PubMed2000

Gravity cue has implicit effects on human behavior.

Gravity modifies us without our knowing it. Possible functional disabilities of eye, head and body movements were investigated under 1 G and microgravity environments to evaluate the gravity cue for human behavior. The system for visual stability might be explained from the viewpoint of ordination between eye and head under microgravity. It is important ascertain the significance of gravity in the maintenance of human visual stability. Coordination of eye position and head motion behavior by neck muscle discharge was examined in the mission SL-J, as well as a subjective evaluation of visual stability during spaceflight. The results shows that: 1) poor performance of eye movement can be observed; 2) unusual neck muscle activity can be observed; 3) there is decreased visual stability in microgravity; and 4) egocentric body axis is emphasized under microgravity conditions.

Eye Movements↗
PubMed1992

Altered gravity conditions affect early EGF-induced signal transduction in human epidermal A431 cells.

Epidermal growth factor (EGF) activates a well-characterized signal transduction cascade in human A431 epidermal carcinoma cells. Among the early responses evoked by EGF are receptor clustering, cell rounding, and early gene expression. These processes have been studied under various gravity conditions. In addition, we have investigated signalling pathways as induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), forskolin, and A23187 that bypass the EGF receptor, but mimic the partial activation of signal transduction pathways. Hypergravity, simulated microgravity, and real microgravity have been obtained by means of centrifuge, fast-rotating clinostat, and sounding rocket, respectively. EGF-induced c-fos gene expression is suppressed in simulated microgravity (clinostatting) and even more so in real microgravity, while hypergravity increases early gene expression. This indicates that gravity inhibits early EGF-induced signal transduction. However, neither microgravity nor clinostatting affect EGF-induced EGF receptor clustering, suggesting that inhibition of EGF-induced signal transduction by microgravity and clinostatting is independent of EGF receptor clustering. EGF-induced cell rounding is enhanced under clinostatting, while hypergravity does not significantly influence this process. Furthermore, both under clinostatting and real microgravity, EGF- and TPA-induced c-fos expression is decreased, while forskolin and A23187-induced c-fos expression remains unaltered. These observations demonstrate that gravity affects specific components in the EGF-induced signal transduction circuitry, in particular the protein kinase C pathway which is common to EGF and TPA activated intracellular signalling.

Calcimycin↗
PubMed1993

Postural control of fish related to gravity input.

The disappearance of gravity input during space flight causes many functional disorders in animal and human postural control system. On the other hand, it has been shown that these functional deficits reduce or disappear with time and adapt to weightlessness. Unusual fish behavior was reported during the first few days of orbit flight and also during postflight recovery in Skylab 3 experiment. Similar fish behavior was observed in microgravity obtained during the parabolic flight of airplane. These results suggest that fish might provide a good model for investigating adaptation of sensory-motor interaction in microgravity. The fish generally show a "dorsal light response (DLR)" indicating how these postural mechanisms concern with the environment. That is, when a light is presented laterally, a fish rolls its dorsal surface toward the light an equilibrium point between the gravity vector and the light source vector. In addition, the DLR after bilaterally labyrinthectomy or changes of the DLR in microgravity show the involvement of other factors related to the changes of gravity. In this investigation, the behavioral changes of bilaterally labyrinthectomized (BL) and unilaterally labyrinthectomized (UL) fish adapted for more than 3 months on the ground postoperatively were used to analyze whether buoyancy was affected by injecting of a contrast medium into the swimming bladder.

Adaptation, Physiological↗
PubMed1994

Artificial gravity in space flight.

Clearly, physiologic adaptation to terrestrial life for all animals is assured only by frequent encounters with gravity. Indeed, upon exposure to weightlessness in space flight, losses of physiologic functions quickly begin. Some physiologic parameters change more rapidly than others, but the deconditioning process starts rapidly. The rates of functional losses for all affected parameters are interesting in that they appear to approach a limit; i.e., losses of these functions may not continue until indefinitely. The regulation of this functional asymptotic response to space is not known, but probably based on functional requirements of the body to life itself and perhaps genetic expression. The latter controlling mechanism (DNA) functions only on aquatic (weightless) animals on Earth--land animals must stimulate these physiologic functions as they relate to gravity on a regular frequent basis. This loss of regulation upon entering the weightless environment is fascinating since land-based animals including the humans have evolved from millions (perhaps billions) of years of terrestrially adapted ancestors. One would expect some DNA involvement in the regulation of its physiology, but it appears to be absent. Therefore, if the functional debilitation of space is to be denied, we must begin to understand the adaptation process of the sole basis for the control of our physiologic processes on land; i.e., how gravity regulates our biologic functions. To learn about this regulatory mechanism, some inquiry into how aquatic animals first adapted to living on land might be helpful.

Adaptation, Physiological↗
PubMed1989

Gravitropism in a starchless mutant of Arabidopsis: implications for the starch-statolith theory of gravity sensing.

The starch-statolith theory of gravity reception has been tested with a mutant of Arabidopsis thaliana (L.) Heynh. which, lacking plastid phosphoglucomutase (EC 2.7.5.1) activity, does not synthesize starch. The hypocotyls and seedling roots of the mutant were examined by light and electron microscopy to confirm that they did not contain starch. In upright wild-type (WT) seedlings, starch-filled plastids in the starch sheath of the hypocotyl and in three of the five columellar layers of the root cap were piled on the cell floors, and sedimented to the ceilings when the plants were inverted. However, starchless plastids of the mutant were not significantly sedimented in these cells in either upright or inverted seedlings. Gravitropism of light-grown seedling roots was vigorous: e.g., 10 degrees curvature developed in mutants rotated on a clinostat following a 5 min induction at 1 g, compared with 14 degrees in the WT. Curvatures induced during intervals from 2.5 to 30 min were 70% as great in the mutant as the WT. Thus under these conditions the presence of starch and the sedimentation of plastids are unnecessary for reception of gravity by Arabidopsis roots. Gravitropism by hypocotyls of light-grown seedlings was less vigorous than that by roots, but the mutant hypocotyls exhibited an average of 70-80% as much curvature as the WT. Roots and hypocotyls of etiolated seedlings and flower stalks of mature plants were also gravitropic, although in these cases the mutant was generally less closely comparable to the WT. Thus, starch is also unnecessary for gravity reception in these tissues.

Arabidopsis↗
PubMed2001

[Biomedical problems of artificial gravity: overview and challenge].

The limitations of the currently used exercise-based countermeasures and the scientific rationale for the gravity-based countermeasures are addressed. Then, an overview of the physiological effects and requirements for the two types of artificial gravity (AG), i.e., the continuous AG provided by full-time spinning of the entire space system/habitat and the intermittent AG by incorporating a short-arm centrifuge into the spacecraft, is presented. Finally, significance and challenge faced in future research on biochemical problems of artificial gravity are discussed.

Adaptation, Physiological↗
PubMedDate not supplied

[Correlation between osmolarity and specific gravity of urine. Changes caused by the presence of abnormal solutes].

There is a high correlation index (0.97) in the measurement of urine osmolality and specific gravity in healthy children and adults and in children with renal disease without heavy proteinuria or glucosuria. This is a useful tool, because osmometers are not used in many laboratories, but specific gravity is of general use, so that urine concentration in mOsm/kg. can be derived from the specific gravity. The same parameters in urines with heavy proteinuria or glucosuria were also measured and the correlation index and the modifications per gram of abnormal solute that should be applied in order to obtain the correct urine concentration figures, were established.

Adult↗
PubMed1976

The evolutionary role of gravity.

Analysis of the part played by gravity in development in the organic world shows that this factor has had an impact on evolution. All terrestrial organisms, including man, have adapted themselves to gravity by developing a number of important features of their composition and functions. Variations of gravitational field in any direction bring about numerous changes in organisms, ranging from metabolism to changes in more conservative systems which also include hereditary structures. Gravitational forces determine the form and the size of organisms, the development of skeletal supporting organs, and energetics. The study of the role of gravity in the variability of the organic world will be of great importance for long-term systems of life support and for work on space orbital stations or at bases on the moon and planets where gravitational forces may differ greatly those from on the earth.

Adaptation, Biological↗
PubMed2000

Search for gravity-responsive genes by PCR-based mRNA differential display in human cells.

Mechanisms of molecular responses of human cells to gravity change and/or space radiation are one of the most important physiological problems in space science. We have previously reported that expression levels of several genes are changed in cultured human cells after UVC irradiation, and a few of those genes are responsible for UVC sensitivity. In this study, to find candidates for genes that play roles in susceptibility of human cells to gravity stressors, including those responsible for genetic stability in humans, we analyzed genes expressed differentially after gravity stress in human cells, using a PCR-based mRNA differential display (D.D.) method. Cells used were RSa and its variant cell lines, with discrepant sensitivity to radiation cell-killing and mutagenicity [correction of mutagenecity].

Cell Line↗
PubMed2003

Ionic signaling in plant gravity and touch responses.

Plant roots are optimized to exploit resources from the soil and as each root explores this environment it will encounter a range of biotic and abiotic stimuli to which it must respond. Therefore, each root must possess a sensory array capable of monitoring and integrating these diverse stimuli to direct the appropriate growth response. Touch and gravity represent two of the biophysical stimuli that plants must integrate. As sensing both of these signals requires mechano-transduction of biophysical forces to biochemical signaling events, it is likely that they share signal transduction elements. These common signaling components may allow for cross-talk and so integration of thigmotropic and gravitropic responses. Indeed, signal transduction events in both plant touch and gravity sensing are thought to include Ca(2+)- and pH-dependent events. Additionally, it seems clear that the systems responsible for root touch and gravity response interact to generate an integrated growth response. Thus, primary and lateral roots of Arabidopsis respond to mechanical stimuli by eliciting tropic growth that is likely part of a growth strategy employed by the root to circumvent obstacles in the soil. Also, the mechano-signaling induced by encountering an obstacle apparently down-regulates the graviperception machinery to allow this kind of avoidance response. The challenge for future research will be to define how the cellular signaling events in the root cap facilitate this signal integration and growth regulation. In addition, whether other stimuli are likewise integrated with the graviresponse via signal transduction system cross-talk is an important question that remains to be answered.

Arabidopsis↗
PubMedDate not supplied

[The evaluation of the specific gravity of Giardia duodenalis and Entamoeba coli cysts].

Cysts of Giardia duodenalis and Entamoeba coli were observed as for floatability in sucrose solutions of different specific gravity, contained in counting-chambers of 0.17 mm height. The cysts that floated and those that sedimented were counted and then calculated the respective percentage. Floatability differences of the cysts of each species were not considerable. Solutions of specific gravity 1,200 kg/m3 made 88.49% of G. duodenalis cysts and 95.71% of E. coli cysts float. The greater values of floatability were associated to specific gravity 1,250 kg/m3 and were 89.15% and 98.59% for cysts of G. duodenalis and E. coli, respectively.

Animals↗
PubMedDate not supplied

[Altered gravity affects subnucleolus localization of fibrillarin and NopA64, the most important proteins of rRNA processing].

Fibrillarin and plant nucleolin homologue NopA64 are two important nucleolar proteins involved in pre-rRNA processing. To understand better the effects of the altered gravity environment on the nucleolus functioning we have investigated the location of fibrillarin and NopA64 in nucleolar subcomponents of cress (Lepidium sativum L.) root meristematic cells grown under simulated microgravity that was compared to the control cells grown in normal conditions at I g. Cress fibrillarin was first shown to have the molecular weight 41 kDa. Both fibrillarin and NopA64 in the cress cell nucleolus are located in the zones known to contain processing pre-rRNA molecules as it has been previously reported in other species. The data confirm participation of these proteins in processomes--RNP complex particles involved in pre-rRNA processing. Under altered gravity a decrease in the quantity of both fibrillarin and NopA64 in the transition zone between fibrillar centres and the dense fibrillar component was observed, compared to control, which could point out to a lowering of the level of early pre-rRNA processing in these experimental conditions. This decrease was also detected in the bulk of the dense fibrillar component. These data support the idea that altered (reduced) gravity results in lowering the level of functional activity of the nucleolus.

Cell Nucleolus↗
PubMed1991

[Exercise-induced pathophysiological changes in asthmatic children. VIII. The changes of specific gravity of peripheral eosinophils and serum cortisol levels].

In order to investigate the mechanism of exercise-induced asthma (EIA) from the aspect of eosinophil function, we determined the changes in the peripheral eosinophil count and the specific gravity of the eosinophils in EIA patients, and also as a parameter of endocrine function, we determined the serum cortisol level. All parameters were analyzed in respect to time before and after inducement of exercise. The subjects selected for this study were 14 asthmatic children, an EIA positive group consisting of 8 subjects and 6 subjects in an EIA negative group. Eosinophil counts with a specific gravity less than 1.0825 gm/ml were recorded in respect to the time sequence of 15, 30, and 60 minutes after inducement of exercise. The eosinophil counts recorded were significantly higher in the EIA positive group in comparison to the EIA negative group. With progression of time after inducement of exercise, the number of eosinophils observed with a specific gravity of less than 1.0825 gm/ml tended to increase in the EIA positive group when compared to the results recorded before inducement of exercise. In respect to the course of time, 15 minutes after inducement of exercise, the serum cortisol level tended to decrease. At the point of 7 hours after inducement of exercise, the serum cortisol levels in the EIA positive group were significantly lower than the EIA negative group. These findings suggest that eosinophils and the endocrine system play an important role in EIA.

Adolescent↗
PubMed1987

Quantitative measurements of retinal edema by specific gravity determinations.

We have quantified retinal edema in rat by specific gravity measurements in vitro. Specific gravity corresponds to tissue water content, which is increased in retinal edema. The gravimetric analysis of retinal edema corresponds well with light and transmission electron microscopy and radiolabelled albumen studies. Specific gravity measurements are the standard method to measure brain edema and are also applicable to the measurement of retinal edema.

Animals↗
PubMed1985

[Evaluation of a method for determining the specific gravity of urine with a reagent strip].

The performance of a new reagent strip method for determining the urine specific gravity was evaluated. 342 clinical specimens were assayed in duplicate by the new method and by the "falling drop" technique. The reproducibility (two lots of strips, four operators) was very good (96.2 per cent agreement between replicates within a range of 0,0100 specific gravity units). The correlation with the comparative method was satisfactory [81,2 per cent concordance within a range of 0,0100 specific gravity units]. No interference was found from ketones, blood or urobilinogen. The influence of proteins and glucose is discussed. The practical advantages of the new method are described.

Acute Kidney Injury↗