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PubMed1991

Influence of hypergravity on the pH profile and proteolytic activity of the avian gastrointestinal tract.

The present study deals with the effect of hypergravity (2xg) on the pH and on the proteolytic activity in the digesta of the gastrointestinal tract of Japanese quails during intense growth. The birds were raised on a semisynthetic diet containing free amino acids (A) and a commercial diet (B). During days 35 till 40 post-hatching the quails were exposed to hypergravity (2xg) using a specially designed centrifuge. On days 40 (experimental group, 2xg) and 41 (control group, 1xg) the animals were sacrificed. The pH of the digesta in various segments of the gastrointestinal tract was measured by means of a semi-microelectrode. Total proteolytic activity was determined by means of azo-dye-modified proteins serving as general proteolytic substrates. Hypergravity leads in general to an alkalization of digesta in various parts of the gastrointestinal tract. In case of the gizzard and duodenum (diet A) and also in the distal jejunum (diet B) the differences are significant. With both diets, hypergravity leads to a considerable decrease in the total proteolytic activity. The reduction is most expressed in the duodenum and jejunum. Changes in the pH of digesta compensate for the decrease in the proteolytic activity. This may explain why hypergravity per se does not seem to impair growth of the Japanese quails.

Amino Acids↗
PubMed1998

The white blood cell line: changes induced in mice by hypergravity.

The effect of hypergravity on the white blood cell (WBC) line of mice was investigated by use of horizontal centrifuge. Several sets of experiments were performed, in which the parameters measured were the WBC and differential cell count in the peripheral blood. In another experiment, lymphocyte counts from the spleen, lymph nodes, and the thymus were measured. The needed samples were taken from the mice during a stay of 7-40 days under a hypergravity of 1.6G. The test groups that were placed on the arms of the centrifuge (1.6G) were compared with stationary control groups (1G) and a rotating control group located at the center of the centrifuge (1G). Such a comparison revealed the test animals to be deficient on all counts, to wit, showing a decrease in total number of WBC's, a decrease in lymphocyte number in the peripheral blood and a decrease in the number of lymphocyte in the spleen and thymus. The decrease of lymphocytes in peripheral blood was characterized by two different slopes--an early and temporary decrease at the first days of the experiment evident in both test and rotating control groups followed by a temporary increase, and a later persistent decrease, evident only in the test group, while in the rotating control lymphocyte counts reverted to normal. There were no significant differences in monocyte or neutrophil counts, except for a temporary increase in the number of neutrophils which peaked on the seventh day. In order to evaluate the effect of hypergravity on restoration of hematopoiesis following hematopoietic suppression, 5-fluoro-uracil (5-FU) was administered i.v. to both the experimental and control mice. Suppression of bone marrow was observed in all groups injected with 5-FU, but while there was later an increase in cell counts in the control groups, there was no such increase in the test group subjected to hypergravity.

Animals↗
PubMed1999

Hypergravity stimulates collagen synthesis in human osteoblast-like cells: evidence for the involvement of p44/42 MAP-kinases (ERK 1/2).

The formation and organization of skeletal tissue is strongly influenced by mechanical stimulation. There is increasing evidence that gravitational stress has an impact on the expression of early response genes in mammalian cells and may play a role in the formation of extracellular matrix. In particular, osteoblasts may be unique in their response to gravitational stimuli since in these cells microgravity has been reported to reduce collagen synthesis, while in fibroblasts the opposite effect was observed. Here, we have investigated the influence of hypergravity induced by centrifugation on the collagen synthesis of human osteoblast-like cells (hOB) and studied the possible involvement of the mitogen-activated protein (MAP) kinase signaling cascade. Collagen synthesis was significantly increased by 42+/-16% under hypergravity at 13 x g, an effect paralleled by the enhanced expression of the collagen I alpha 2 (COL1A2) mRNA. No difference was seen in the proportion of collagen types I, III, and V synthesized by hOB. Hypergravity induced a markedly elevated phosphorylation of the p44/42 MAP kinases (ERK 1/2). The inhibition of this pathway suppressed the hypergravity-induced stimulation of both collagen synthesis as well as COL1A2 mRNA expression by about 50%. Our results show that the collagen synthesis of non-transformed hOB is stimulated under hypergravitational conditions. This response appears to be partially mediated by the MAP kinase pathway.

Base Sequence↗
PubMed2000

Changes in the apoplastic pH are involved in regulation of xyloglucan breakdown of azuki bean epicotyls under hypergravity conditions.

Hypergravity inhibited elongation growth of azuki bean (Vigna angularis Ohwi et Ohashi) epicotyls by decreasing the mechanical extensibility of cell walls via the increase in the molecular mass of xyloglucans [Soga et al. (1999) Plant Cell Physiol. 40: 581]. Here, we report that the pH value of the apoplastic fluid in epicotyls increased from 5.8 to 6.6 by hypergravity (300 x g) treatment. When the xyloglucan-degrading enzymes extracted from cell walls of the 1 x g control epicotyls were assayed in buffer at pH 6.6 and 5.8, the activity at pH 6.6 was almost half of that at pH 5.8. In addition, when enzymically active cell wall preparations obtained from 1 x g control epicotyls were autolyzed in buffer at pH 5.8 and 6.6 and then xyloglucans were extracted from the autolyzed cell walls, the molecular mass of xyloglucans incubated at pH 5.8 decreased during the autolysis, while that at pH 6.6 did not change. Thus, the xyloglucans were not depolymerized by autolysis at the pH value (6.6) observed in the hypergravity-treated epicotyls. These findings suggest that in azuki bean epicotyls, hypergravity decreases the activities of xyloglucan-degrading enzymes by increasing the pH in the apoplastic fluid, which may be involved in the processes of the increase in the molecular mass of xyloglucans, leading to the decrease in the cell wall extensibility.

Biomechanical Phenomena↗
PubMed2001

Dome formation and tubule morphogenesis by Xenopus kidney A6 cell cultures exposed to microgravity simulated with a 3D-clinostat and to hypergravity.

Confluent high-density cell cultures of A6 cells derived from adult male Xenopus kidney exhibit spontaneous dome-formation at 1 g. To determine whether this morphogenetic property is altered by gravity, we used a three-dimensional (3D) clinostat to subject the cells to simulated microgravity, and a centrifuge to subject them to hypergravity. We used the generation orbit control method as the new rotation control system of the 3D-clinostat, not the random method. The growth of A6 cells was significantly enhanced by hypergravity, but significantly reduced by simulated microgravity. Dome formation by A6 cells at high confluence was inhibited under simulated microgravity conditions, whereas hypergravity promoted dome formation and induced tubule morphogenesis, compared to the control at 1 g. These results indicated that changes in gravity influence the morphogenetic properties of A6 cells, such as dome formation and tubule morphogenesis. When dome formation by A6 cells at high confluence was induced spontaneously in the control 1 g culture, the gene expression of the HGF family of pleiotropic factors, such as HGF-like protein (HLP) and growth factor-Livertine (GF-l.ivertine), an epithelial serine protease of channel activating protease 1 (CAP1), and Na+, K+-adenosine triphosphatase (ATPase), increased. Simulated microgravity increased the gene expression of activin A and reduced the gene expression of HLP, GF-Livertine, CAP1, and Na+, K+-ATPase. Hypergravity, on the other hand, decreased the gene expression of activin A and increased the gene expression of HLP, GF-Livertine, CAP1, and Na+, K+-ATPase. These results suggest that the effects of gravitational changes on expression of the HGF family member gene, CAP1, and Na+, K+-ATPase gene may be important for the cell growth, tubule morphogenesis, and dome formation of A6 cells in altered

Animals↗
PubMed1996

Reduction of the elevator illusion from continued hypergravity exposure and visual error-corrective feedback.

Ten subjects served as their own controls in two conditions of continuous, centrifugally produced hypergravity (+2 Gz) and a 1-G control condition. Before and after exposure, open-loop measures were obtained of (1) motor control, (2) visual localization, and (3) hand-eye coordination. During exposure in the visual feedback/hypergravity condition, subjects received terminal visual error-corrective feedback from their target pointing, and in the no-visual feedback/hypergravity condition they pointed open loop. As expected, the motor control measures for both experimental conditions revealed very short lived underreaching (the muscle-loading effect) at the outset of hypergravity and an equally transient negative aftereffect on returning to 1 G. The substantial (approximately 17 degrees) initial elevator illusion experienced in both hypergravity conditions declined over the course of the exposure period, whether or not visual feedback was provided. This effect was tentatively attributed to habituation of the otoliths. Visual feedback produced a smaller additional decrement and a postexposure negative after-effect, possible evidence for visual recalibration. Surprisingly, the target-pointing error made during hypergravity in the no-visual-feedback condition was substantially less than that predicted by subjects' elevator illusion. This finding calls into question the neural outflow model as a complete explanation of this illusion.

Adult↗
PubMed1998

Cortical bone responses to 2G hypergravity in growing rats.

BACKGROUND: Rat cortical bone adaptation to chronic hypergravity (2G) was studied using young growing male Wistar rats (60 d). METHODS: Animals (10 rats) were subjected to chronic hypergravity (14 d) in order to understand the plastic nature of bone under a constant hypergravity stress using a special rodent habitat that was attached to a 12-ft. radius centrifuge. Also, an equal number of stationary controls were housed in a rodent vivarium containing identical cages that were used for centrifugation. After 14 d of centrifugation, femur bones were excised and prepared for morphological and biochemical measurements. RESULTS: Results showed that 2G had significantly shortened the femurs (3%) and reduced the cortical bone area (13%). In particular, hypergravity induced significant reductions in the thicknesses of cortical bone at the anterior (13%) and medial regions (15%) of the mid-diaphysis. However, femoral bone density, collagen and calcium concentrations were unaltered. The content of mature, stable bone collagen cross-links hydroxylysylpyridinoline (HP), lysylpyridinoline (LP), were significantly greater in bones from centrifuged animals. CONCLUSION: Our findings suggest that short term exposure to 2G does not enhance bone formation or induce changes in cortical bone composition, or alter specific gravity. These data also suggest that bone maturation as reflected by collagen cross-linking is upregulated. However, it is undetermined at this time whether the enhanced content of mature bone collagen in the centrifuged rats is a result of either an increased rate of cross-linking or reduction in the degradation of "older collagen."

Adaptation, Physiological↗
PubMed2001

Restoration of gravitropic sensitivity in starch-deficient mutants of Arabidopsis by hypergravity.

Despite the extensive study of plant gravitropism, there have been few experiments which have utilized hypergravity as a tool to investigate gravisensitivity in flowering plants. Previous studies have shown that starch-deficient mutants of Arabidopsis are less sensitive to gravity compared to the wild-type (WT). In this report, the question addressed was whether hypergravity could restore the sensitivity of starch-deficient mutants of Arabidopsis. The strains examined include a WT, a starchless mutant and a reduced-starch mutant. Vertical orientation studies with dark-grown seedlings indicate that increased centrifugal acceleration improves orientation relative to the acceleration vector for all strains, even the WT. For starchless roots, growth of seedlings under constant 5 g acceleration was required to restore orientation to the level of the WT at 1 g. In contrast, approximately 10 g was required to restore the orientation of the starchless mutant hypocotyls to a WT level at 1 g. Examination of plastid position in root cap columella cells of the starchless mutant revealed that the restoration of gravitropic sensitivity was correlated with the sedimentation of plastids toward the distal cell wall. Even in WT plants, hypergravity caused greater sedimentation of plastids and improved gravitropic capability. Collectively, these experiments support the hypothesis of a statolith-based system of gravity perception in plants. As far as is known, this is the first report to use hypergravity to study the mechanisms of gravitropism in Arabidopsis.

Arabidopsis↗
PubMed1995

Effects of hypergravity on the cell shape and on the organization of cytoskeleton and extracelluar matrix molecules of in vitro human dermal fibroblasts.

In vitro human dermal fibroblasts were submitted to normal gravity (1 g) or to chronic hypergravity ranging from 2 to 20 g for 8 days. Changes only appeared above 15 g. The majority of 20 g-subjected cells showed fine filipods in the shape of a star whereas most control cells had rounded shapes and spread by forming lamellipodia. Indirect immunofluorescence staining of vinculin, alpha-actinin and actin stress fibers showed changes of the arrangement anchoring points of stress fibers under hypergravity. Tubulin staining showed that the centrosomal material generally located above the nucleus in control cells had migrated to the nucleus side in 20 g-exposed cells. After 8 d of culture under 20 g hypergravity the thickness of fibronectin network seemed to be increased and bundles of fibrils appeared linking ordered arrays of fibers. The fibrils of collagen I formed better delimited and thicker bundles of fibers. We may assume that 20 g hypergravity can induce changes in fibroblast cell shape, migration way, and anchorage leading to a reorganization of extracellular matrix without concomitant change of cell proliferation.

Actin Cytoskeleton↗
PubMed1991

Effects of hypergravity on adherent human cells.

In recent years, accumulating evidence has shown that microgravity or hypergravity may affect cell growth and differentiation. Since it is not easy to carry out researches in space or to simulate weightlessness on earth, we conducted experiments on simulated hypergravity (2 to 15 g) by using a centrifuge (radius: 80 cm; speed motor: 180 rpm). We looked for the effects of chronic hypergravity (7 to 10 days) on cultures of three human cell lines: lung or dermic fibroblasts and lung adenocarcinoma A 549 cells. The results showed a significant decrease (10-20%, P<0.05) in cell proliferation connected to a significant decrease (20-50%, P<0.01) in culture DNA content under hypergravity, but only for lung fibroblasts. The protein content was never disturbed. Dermic fibroblast elastase activity was enhanced (8-13%, P<0.02) under 15 g. Total phospholipid content as well as relative amounts of phospholipid components, analysed by thin layer chromatography, were unchanged in A 549 cells.

Adenosarcoma↗
PubMed1994

Induction of early response genes by hypergravity in cultured mouse osteoblastic cells (MC3T3-E1).

Hypergravity as low as 50g transiently stimulated cultured mouse osteoblastic cells (MC3T3-E1) to induce early response genes such as c-fos and egr-1, whereas expression of c-jun was marginally affected. The maximum induction of c-fos required more than 90g, but egr-1 induction became maximum below 50g. Staurosporin inhibited the induction of c-fos by hypergravity almost completely at a concentration of 0.1 microM, but it inhibited the induction of egr-1 only partially. In cells pretreated with 12-O-tetradecanoylphorbol 13-acetate, induction of c-fos by hypergravity was almost completely abolished, whereas that of egr-1 was not affected. Activity of protein kinase C seemed to be activated in cells centrifuged at 900g. These results indicate that hypergravity stimulates multiple signal transduction cascades that are connected with the expression of early response genes.

Animals↗
PubMed1998

Influence of hypergravity on the development of monoaminergic systems in the rat spinal cord.

We have investigated in this study the influence of a moderate hypergravity (1.8 G) on the development of monoaminergic projections to the spinal cord in the rat. Pregnant dams and their offspring were submitted to hypergravity from day 11 of gestation to postnatal day 15. Some animals were sacrificed at birth, other at postnatal day 15 and other after 8 months of normal gravity. In newborn animals, a substantial delay of the development of monoaminergic projections to the spinal cord was evidenced. In 15 days and 8 months animals, the pattern of innervation appeared anarchic, with numerous dystrophic profiles, mainly of serotonergic system. Ultrastructural examination of serotonergic projections revealed a paucity of synapses, and the frequent enveloping of serotonergic boutons by thin astrocytic profiles. We conclude that rats submitted to hypergravity during the critical period of onset of monoaminergic projections to the spinal cord are affected durably in the organization and the ultrastructure of these projections. Future studies are directed to the functional analysis of hypergravity animals, and to the influence of microgravity on the same system.

Animals↗
PubMed2000

A mild stress due to hypergravity exposure at young age increases longevity in Drosophila melanogaster males.

Drosophila melanogaster flies were exposed to hypergravity starting at two days of age, the range of gravity levels used being 2.58-7.38 g. No longevity change was observed for exposures of less than 14 days. The longevity of males increased if they were submitted to hypergravity for durations ranging from 14 to 24 days. This increase in longevity was never observed in females. The positive effect of exposure to hypergravity has been replicated in two laboratories using two wild-type strains and different rearing conditions. A short hypergravity exposure seems to be a mild stress, yielding positive effects on longevity. This is in accordance with two previous studies showing a slight longevity increase after heat shock in the nematode Caenorhabditis elegans and in Drosophila melanogaster.

Animals↗
PubMed2001

Effects of hypergravity exposure on the developing central nervous system: possible involvement of thyroid hormone.

The present study examined the effects of hypergravity exposure on the developing brain and specifically explored the possibility that these effects are mediated by altered thyroid status. Thirty-four timed-pregnant Sprague-Dawley rats were exposed to continuous centrifugation at 1.5 G (HG) from gestational Day 11 until one of three key developmental points: postnatal Day (P) 6, P15, or P21 (10 pups/dam: 5 males/5 females). During the 32-day centrifugation, stationary controls (SC, n = 25 dams) were housed in the same room as HG animals. Neonatal body, forebrain, and cerebellum mass and neonatal and maternal thyroid status were assessed at each time point. The body mass of centrifuged neonates was comparatively lower at each time point. The mass of the forebrain and the mass of the cerebellum were maximally reduced in hypergravity-exposed neonates at P6 by 15.9% and 25.6%, respectively. Analysis of neonatal plasma suggested a transient hypothyroid status, as indicated by increased thyroid stimulating hormone (TSH) level (38.6%) at P6, while maternal plasma TSH levels were maximally elevated at P15 (38.9%). Neither neonatal nor maternal plasma TH levels were altered, suggesting a moderate hypothyroid condition. Thus, continuous exposure of the developing rats to hypergravity during the embryonic and neonatal periods has a highly significant effect on the developing forebrain and cerebellum and neonatal thyroid status (P < 0.05, Bonferroni corrected). These data are consistent with the hypothesized role of the thyroid hormone in mediating the effect of hypergravity in the developing central nervous system and begin to define the role of TH in the overall response of the developing organism to altered gravity.

Animals↗
PubMed1989

Reduction of G1 phase duration and enhancement of c-myc gene expression in HeLa cells at hypergravity.

We have found that hypergravity stimulates the proliferation of HeLa cells through reduction of the G1 phase duration, concomitant with enhancement of c-myc gene expression. HeLa cells were grown in monolayer in culture flasks that were centrifuged to generate a constant 18, 35 or 70 g at 37 degrees C for up to 4 days. The cell proliferation was enhanced at 18, 35 and 70 g, most notably at 35 g. Cell cycle analyses with [3H]thymidine (TdR)-colcemid treatment showed that the cell generation time in the 35 g culture was reduced by 17% as compared to the control, which was attributed to a 26% reduction of the G1 phase duration. No differences were observed in the duration of the S, G2 and M phases or in the [3H]TdR incorporation per S phase cell between the 35 g culture and the control. The induction of c-myc gene expression was investigated by RNA blot hybridization during a 15-360 min exposure of cells to 18, 35 and 70 g. Elevated levels of c-myc mRNA were observed after a 15-min exposure, and maintained after a 360-min exposure at all hypergravities examined. The highest induction rate of c-myc mRNA was 3.8-fold higher than the control after a 120-min exposure to 35 g. The 35 g condition was the most effective hypergravity for stimulating both cell proliferation and c-myc gene expression. Our study suggests that the appropriate level of hypergravity stimulates HeLa cell proliferation by reducing the G1 phase duration without affecting DNA synthesis rate, mediated through induction of c-myc gene expression.

Cell Cycle↗
PubMed1993

Ultrastructure of the parathyroid gland of magnesium-treated golden hamster exposed to a hypergravity environment: a stereological study.

The ultrastructure of the parathyroid glands of magnesium-treated golden hamsters exposed to a 5 gravity environment was studied. In the parathyroid glands of the magnesium-treated animals exposed to a hypergravity environment, the Golgi complexes and cisternae of the granular endoplasmic reticulum were increased as compared to those of the magnesium-treated animals and decreased as compared to those of animals exposed to a hypergravity environment, but were almost the same as those of the control animals. In the control and experimental animals, the chief cells were rich in free ribosomes and mitochondria. In addition, numerous secretory granules were situated close to the plasma membrane in the magnesium-treated animals exposed to a hypergravity environment. These observations suggest that the synthesis of parathyroid hormone may be stimulated in the parathyroid glands of magnesium-treated hamsters exposed to hypergravity environment.

Animals↗
PubMed1991

[Effects of hypergravity on migration, proliferation and function of mouse osteoblastic cell line MC3T3-E1].

The purpose of this study was to investigate the hypergravity-induced responses and their mediators of osteoblastic cell line, MC3T3-E1. The synchronized G1 or the S Phase cells were exposed to 5 and 18 x g hypergravity at 37 degrees C. The migration velocity was measured and the morphology was observed. MC3T3-E1 cells were cultured for 1, 2 or 3 days at 37 degrees C, exposing to 5, 10, 20 and 40 x g hypergravity. The proliferation, prostaglandin E2 (PGE2) production rate and alkaline phosphatase (ALPase) activity were measured. The results were as follows: 1) In the G1 phase of the cell cycle, the migration of MC3T3-E1 cells was increased by 18 x g. In the S phase, the morphology altered depending on the g-stress. 2) The proliferation of MC3T3-E1 cells was enhanced at 20 and 40 x g but reduced at 10 x g. The proliferation of HeLa cells and JTC-12 cells was also enhanced at 40 x g. 3) Indomethacin (10(-5)M) reduced the proliferation of MC3T3-E1 cells induced by 40 x g. But indomethacin (10(-5)M) did not reduce the proliferation of HeLa cells. 4) The increase of the released PGE2 from the cells depended on the time (1-8h) and the gravity (1-40 x g). 5) The increase of the ALPase activity of MC3T3-E1 cells also depended on the gravity. These results suggest that the hypergravity enhanced the proliferation of MC3T3-E1 cells via PGE2-mediated mechanism.

Alkaline Phosphatase↗
PubMed1990

Electron microscopic study of the parathyroid gland of the calcium-treated hamster subjected to hypergravity environment.

The ultrastructure of the parathyroid glands of calcium-treated golden hamsters subjected to 5 gravity environment was studied. In the calcium-treated animals exposed to hypergravity environment, the Golgi complexes and cisternae of the granular endoplasmic reticulum were significantly decreased compared with those of the animals exposed to hypergravity environment only and appeared to increase compared with those of the calcium-treated animals, but were almost similar to those of the control animals. In addition, many chief cells contained some prosecretory granules in the Golgi areas, some secretory granules situated close to the plasma membrane and many lysosomes. The morphology of the parathyroid glands in the calcium-treated animals exposed to hypergravity environment resembled that of the control animals. These results suggest that the parathyroid glands suppressed by treatment of calcium and stimulated in response to hypergravity environment may indicate the secretory activity of the parathyroid glands of the control animals.

Animals↗