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PubMed1994

Sympathetic nervous activity and cardiovascular variability after a 3-day tail suspension in rats.

The effects of a 3-day tail suspension on central and peripheral sympathetic activity were studied in rats by determining the in vivo noradrenaline (NA) turnover in the brain cell groups involved in central blood pressure control (A1, A2, A5 and A6) and in two peripheral organs, heart and kidneys. In addition, cardiovascular parameters and their variabilities were investigated by recording blood pressure (BP) and heart rate (HR) before and after suspension. These measurements were processed by spectrum analysis to assess the influence of tail suspension on autonomic balance. The NA turnover in the suspended rats was markedly reduced in A2 (-49%, P < 0.01) and A5 (-38%, P < 0.01) nuclei but unchanged in A1 and A6 cell groups compared with the control rats. Peripheral NA turnover was decreased in cardiac atria (-44%, P < 0.001) and ventricles (-27%, P < 0.01) while it was unchanged in kidneys after suspension. The BP, HR and their variabilities were similar in both groups of animals and showed no changes after suspension compared with baseline values. Spectrum analysis of BP and HR in our conscious suspended rats revealed no changes in power spectrum density or in peak frequencies. The discrepancy between the decrease in central sympathetic activity and the absence of changes in cardiovascular parameters after tail suspension raises the question of the validity of the tail suspended rat model when studying the cardiovascular deconditioning observed in humans after an exposure to actual or simulated weightlessness.

Animals↗
PubMed1994

Changes in fibre-type composition and myosin heavy-chain IId isoform in rat soleus muscle during recovery period after hindlimb suspension.

We examined the changes in myosin heavy-chain (HC) isoforms and fibre-type composition in rat soleus muscle using both myosin adenosine triphosphatase staining and sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS-PAGE) analyses during the recovery period after 4 weeks of hindlimb suspension. Although there was no change in type IIc fibres after the suspension, an increase in this type of fibres was observed during the 1- to 4-week recovery period. The increase in type IIc fibres was considered to be due to a shift from type IIa to IIc fibres. The SDS-PAGE analysis revealed the presence of the HC IId isoform, which was not observed in the control muscle, after a 4-week hindlimb suspension. The HC IId isoform gradually decreased over 3 weeks of recovery and disappeared in the 4th week of recovery after the suspension. These results suggest that the hypogravity conditions induced by hindlimb suspension stimulated the synthesis of the HC IId isoform, whereas an increase in mechanical load to the muscle accelerated the degradation of the HC IId isoform and the synthesis of type IIc fibres during the recovery period after hindlimb suspension.

Animals↗
PubMed1993

Relationship between myosin heavy chain IId isoform and fibre types in soleus muscle of the rat after hindlimb suspension.

The relationship between the myosin heavy chain (HC) IId isoform and histochemically defined fibre types was investigated in the rat soleus muscle after hindlimb suspension. After 4 weeks of suspension, right and left muscles were removed and fibre type composition and total fibre number were examined by histochemical myosin adenosine triphosphatase staining sections. Myosin HC isoforms were analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. After the suspension, there was a significant decrease in the percentage of type I fibres and a concomitant increase in that of type IIa fibres. However, the total number of fibres was not affected by suspension. The synthesis of HC IId isoform, which was not found in the control, and the decrease in the ratio of slow type myosin heavy chain isoform (HC I) were observed after suspension. These results would may suggest that the change of fibre type composition was caused by a shift from type I to IIa fibres after suspension. Furthermore, it could be suggested that the synthesis of HC IId isoform occurred during the stage of type shift from type I to IIa fibres.

Animals↗
PubMed1981

Comparative rheology of nucleated and non-nucleated red blood cells. II. Rheological properties of avian red cells suspensions in narrow capillaries.

The flow properties of nucleated avian (duck) red cell suspensions were determined in narrow glass capillaries (internal diameter 5- 11 micrometer) perfused at constant pressure. Measurements were carried out of cellular and suspending fluid flow velocity of dynamic (tube) hematocrit. Comparison with previous measurements on human erythrocyte suspensions showed that the dynamic hematocrit reduction (Fahraeus effect) of avian cell suspensions was significantly more sensitive to changes of hematocrit than observed on the human cells. It was in addition found that the Fahraeus effect is the dominating phenomenon determining the viscosity of the nucleated cell suspensions, in contrast to suspensions of non-nucleated human red cells. Furthermore, the apparent viscosity of the nucleated cell suspensions is significantly higher than that of human blood at equal capillary diameter and tube hematocrit. In the living capillary bed of birds, the unfavourable rheological properties of the nucleated red cells could be compensated for by a low capillary hematocrit and/or a higher capillary density compared to mammalian species.

Animals↗
PubMed1984

Protective effect of bone marrow and spleen suspensions on radiation-induced leukemogenesis in C57BL/6 mice.

The present experiments are an attempt to precise the type and localization of the cells involved in the protective effect of hemopoietic suspensions against the radiation-induced thymic lymphosarcoma (TLS) of C57BL/6 mice. Inocula containing variable numbers of BM or spleen CFUs from 60-day-old and 360-day-old donors were tested. According to their origin, the suspensions differed with respect to the CFU replication rate, the CFU ability to differentiate towards the T lineage and the content of the suspensions in thymic precursors. Two levels of inhibition were observed: BM suspensions from 60-day-old donors containing 1,500 CFUs had the best protective effect: 14.5% of TLS; 1,500 CFUs from 360-day-old donors were slightly but not significantly less efficient (28.5%). The second level of inhibition (36-46% of TLS) was obtained with all the following inocula: a) 1,200 and 300 spleen CFUs or 300 and 95 BM CFUs from 60-day-old donors, b) 1,500 spleen CFUs from aged donors. Seventy-six spleen CFUs from 60-day-old donors, 120 BM or 175 spleen CFUs from aged donors had no effect. These results suggest that in addition to the high replication rate of the BM CFUs as compared with spleen CFUs, cells endowed with an optimal protective effect are present in BM suspensions and are either absent or present in very small amount in spleen suspensions. These cells which induce an early repopulation of the thymus might correspond to thymic precursors.

Animals↗
PubMed1986

Increased yield of mouse mammary tumor virus (MMTV) by cultivation of monolayer-derived mammary tumor cells in suspension.

The MJY-alpha epithelial-like mammary tumor cell line was adapted for cultivation in suspension using a shaker culture technique. Replication of suspension (MJY-beta) cells was more sensitive than monolayer cells to decreases in the concentration of serum in the medium. Comparison of amino acid incorporation and lactate production rates revealed additional differences between monolayer and suspension cultures. In addition, growth in suspension resulted in 10- to 400-fold increases in mouse mammary tumor virus (MMTV) production by the mammary tumor cells. Increases in MMTV yield were detected within 48 h of culture initiation and MMTV production remained elevated throughout 20 cell passages in suspension. Exposure of MJY-beta cells to 14 microM hydrocortisone further increased MMTV yield two- to five-fold. The MJY-beta suspension cultures demonstrated that these epithelial-like cells do not require attachment to a solid substrate for replication or for MMTV production. Loss of structural polarization associated with growth as a monolayer resulted in stimulation of MMTV production greater than and independent of steroid exposure.

Animals↗
PubMed1986

Proteoglycan synthesis in suspension cultures of Swarm rat chondrosarcoma chondrocytes and inhibition by exogenous hyaluronate.

Conditions were established for short-term primary suspension culture of chondrocytes from the Swarm rat chondrosarcoma. Proteoglycan and hyaluronate synthesis on Day 0 to Day 2 in culture was investigated and compared with that for plated cultures. Incorporation of [35S]sulfate into proteoglycans was the same for both suspension and plated cultures. 35S-Proteoglycan synthesis decreased by about 80% between Days 0 and 1 irrespective of culture conditions. Suspension culture chondrocytes synthesized proteoglycans which were very similar to those made in plated cultures, with respect to hydrodynamic size, glycosaminoglycan, chain length, and composition. [3H]Hyaluronate synthesis accounted for 18 and 23% of the total 3H-glycosaminoglycans synthesized from [3H]glucosamine by suspension and plated cultures, respectively. Suspension culture chondrocytes responded to exogenous hyaluronate (1 mg/ml) by reducing their 35S-proteoglycan synthesis by about 50%. [3H]Hyaluronate synthesis was inhibited by 13% under these conditions. The inhibition was dependent on the concentration of exogenous hyaluronate and reached a plateau level within 2 h. Plated chondrocyte cultures showed little or no response to hyaluronate. Suspension cultures of chondrocytes were prelabeled with [3H]lysine and lysed, and a heavy membrane fraction (12,000g) was extracted with the detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate. A Sepharose-hyaluronate affinity gel was used to show that the extract contained hyaluronate binding 3H-labeled proteins and evidence was obtained suggesting that these came from the external face of the plasma membrane.

Animals↗
PubMed1987

Early (1 to 24h) plasma atrial natriuretic factor changes in the rat during antiorthostatic hypokinetic suspension.

Antiorthostatic hypokinetic suspension (AOH) in rat is currently used as an animal model for simulating weightlessness. This maneuver is responsible for a diuresis, a natriuresis and an increase in central venous pressure (CVP). Knowing the role of CVP in atrial natriuretic factor (ANF) secretion, the aim of the study was to examine the early plasma ANF changes during AOH (angle 30-35 degrees) using Morey's model (tail suspension). The rats were divided into 4 groups: 24 population cage (PC), 24 isolated in separate cages (I), 24 were attached by the tail (Morey's model) and remained in the horizontal position (attached horizontal: AH). At the end of this period of 7 d, 12 AH were suspended for 1, 2, 6 and 24 h (AOH) and sacrificed with the controls for plasma ANF determination. Our results show that the level of ANF is significantly (p less than .05) higher in AOH rats after 2 h of suspension (16.6 +/- 2 pg/ml vs 10.9 +/- 1.5). A significant increase is also observed between AOH and AH after 2h of suspension (p less than 0.05). Six hours after suspension ANF presents a sharp decline in AOH and no difference is observed between AOH and AH and I. Morey's tail suspension model seems to be valid for the study of the early hormonal effects of simulated weightlessness for ANF.

Animals↗
PubMed1985

Monitoring of cell viability in suspensions of embryonic CNS tissue and its use as a criterion for intracerebral graft survival.

Neuronal cell suspensions, prepared by trypsination and mechanical disruption from embryonic CNS tissue, are currently used for intracerebral neuronal grafting to deep brain sites. In the present study the viability of suspended neurons from different brain regions has been monitored with a fluorescent vital stain, and studied as a function of time after dissociation and age of the donor rat embryos. Subsequently, the validity of the in vitro viability rates as a criterion for the in vivo survivability of each individual suspension was tested for suspensions prepared from the developing mesencephalon, rich in dopamine-containing neurons. The results indicate that mechanically dissociated embryonic CNS neurons remain viable for several hours in a simple glucose-saline solution at room temperature. The in vitro viability scores declined faster in suspensions prepared from mesencephalon than in those prepared from telencephalon (striatum and basal forebrain), and they declined faster in suspensions prepared from older embryos. The fetal cells were sensitive to the mechanical trauma caused by excessive pipetting, and tissue from older embryos seemed generally more vulnerable in the trypsination-dissociation procedure. The grafting experiments showed a good correlation between the in vitro cell viability counts and in vivo neuronal survival after grafting, indicating that the vital stain, at least under certain conditions, can be used as a simple and practical routine test to check and standardize cell suspensions to be used in intracerebral grafting experiments.

Animals↗
PubMed1995

Finite element analysis of nonlinear pulsatile suspension flow dynamics in blood vessels with aneurysm.

A nonlinear pulsatile suspension flow in a dilated vessel is numerically analysed. Two sets of highly coupled nonlinear partial differential equations governing the suspension flow are numerically solved, to simulate the suspension flow dynamics. A transient velocity-pressure (UVP) finite element method (FEM) and a stable time integration scheme, based on a predictor-corrector strategy, with constant error monitoring are employed in the flow analysis. The pulsatile suspension flow is characterized by analysing the flow, pressure and stress fields. Effects of the nonlinear particulate phase on the nonlinear suspending fluid phase are brought out by comparing the suspension flow results with those of homogeneous flow. Particles are seen to dampen the flow velocity, wall and central axis pressure, pressure gradient and wall shear stress. time-dependent recirculation regions which are sensitive to the presence of particles are seen in the dilated portion of the vessel. These recirculation regions favour thrombogenesis. The nonlinear effects due to the vessel geometry and those due to the convective terms dominate the dampening effect of the particles. These nonlinear effects are depicted through the transverse velocity and pressure plots. Wall shear stresses of suspension flow are not only high but also alternate in direction.

Algorithms↗
PubMed2004

Methotrexate differentially affects growth of suspension and adherent cells.

The effects of low concentrations of methotrexate (MTX) on the growth of suspension (FM3A, 2B4 and THP-1) and adherent (NIH3T3 and V79) cells were compared. The concentration of methotrexate to cause the inhibition of cell growth was lower in suspension cells than in adherent cells. The IC(50) for FM3A, 2B4, THP-1, NIH3T3 and V79 cells were 3.5, 5, 9, 30 and 50 nM, respectively. The inhibition of cell growth was reversed completely by tetrahydrofolate and was fully or significantly reversed by adenosine and thymidine, suggesting that the effects of low concentrations of methotrexate result from the inhibition of biosynthesis of purines and pyrimidines. In suspension cells but not in adherent cells there was a decrease in the levels of S-adenosylmethionine and polyamines after methotrexate treatment. Growth of suspension but not adherent cells was significantly recovered by treatment with S-adenosylmethionine. However, treatment with spermidine did not reverse the effects of methotrexate in any of the cell lines. The preferential inhibitory effect of methotrexate in suspension cells versus adherent cells was due mainly to a more rapid uptake of methotrexate. This may be relevant to the in vivo effects of low doses of methotrexate, which have immunosuppressive and anti-inflammatory effects, because lymphocytes are suspension cells.

Adenosylmethionine Decarboxylase↗
PubMed2005

Transmembrane voltage induced on a cell membrane in suspensions exposed to an alternating field: a theoretical analysis.

We present analytical equations for the transmembrane voltage (DeltaPsi) induced by an alternating field on spherical cells arranged in orderly suspensions. For physiologically normal cells, the cell membrane was assumed to be non-conductive. With increasing alternating field frequency, capacitive property of the cytoplasm and the external medium become increasingly important and thus must be accounted for. Considering the symmetry of the arrayed cells and the tiny volume of the unit cell compared to that of the suspensions, the influence exerted on a unit cell by other cells was posited to be approximately symmetrical with respect to the symmetrical axis. This implies that the shape of the equipotential plane of spherical cells in the suspensions is similar to that of the single cell exposed to the external field, though the value of the potential of both cells should be different. Therefore, the internal field of the cytoplasm and the equivalent body of a unit cell in the suspensions should be approximately constant. This allows for calculating the effective average field in the equivalent body with Maxwell-Wagner and Bruggeman-Hanai equations for low and high cell concentrations, respectively. We investigated the conditions, under which the local electric field of a unit cells in suspension is approximately equal to that of a single cell. Under these conditions the analytical solution for DeltaPsi induced by alternating fields on cells in suspensions can be derived from that of the single cell.

Cell Membrane↗
PubMed2006

The effect of school suspensions and arrests on subsequent adolescent antisocial behavior in Australia and the United States.

PURPOSE: To examine the effect of school suspensions and arrests (i.e., being taken into police custody) on subsequent adolescent antisocial behavior such as violence and crime, after controlling for established risk and protective factors in Victoria, Australia and Washington State, United States (U.S.). METHODS: This article reports on analyses of two points of data collected 1 year apart within a cross-national longitudinal study of the development of antisocial behavior, substance use, and related behaviors in approximately 4000 students aged 12 to 16 years in Victoria, Australia and Washington State, U.S. Students completed a modified version of the Communities That Care self-report survey of behavior, as well as risk and protective factors across five domains (individual, family, peer, school, and community). Multivariate logistic regression analyses investigate the effect of school suspensions and arrests on subsequent antisocial behavior, holding constant individual, family, peer, school, and community level influences such as being female, student belief in the moral order, emotional control, and attachment to mother. RESULTS: At the first assessment, school suspensions and arrests were more commonly reported in Washington, and school suspensions significantly increased the likelihood of antisocial behavior 12 months later, after holding constant established risk and protective factors (adjusted odds ratio [OR] 1.5, 95% confidence interval [CI] 1.1-2.1, p < .05). Predictors of antisocial behavior spanned risk and protective factors across five individual and ecological areas of risk. Risk factors in this study were pre-existing antisocial behavior (OR 3.6, CI 2.7-4.7, p < .001), association with antisocial peers (OR 1.8, CI 1.4-2.4, p < .001), academic failure (OR 1.3, CI 1.1-1.5, p < .01), and perceived availability of drugs in the community (OR 1.3, CI 1.1-1.5, p < .001). Protective factors included being female (OR 0.7, CI 0.5-0.9, p < .01), student belief in the moral order (OR 0.8, CI 0.6-1.0, p < .05), student emotional control (OR 0.7, CI 0.6-0.8, p < .001), and attachment to mother (OR 0.8, CI 0.7-1.0, p < .05). CONCLUSIONS: School suspensions may increase the likelihood of future behavior. Further research is required to both replicate this finding and establish the mechanisms by which school suspensions exert their effects.

Adolescent↗
PubMed2005

Optical properties of dilute hematite/silicone oil suspensions under low electric fields.

Electrorheology (ER) is the name given to a set of phenomena related to the significant changes experienced by the rheological properties of certain fluids and suspensions upon application of external electric fields. It is mostly explained in terms of the formation of particle aggregates as a consequence of field-induced particle-particle interactions. In this work, we explore such structures by investigating the changes in optical absorbance of hematite/silicone oil suspensions associated to the application of an electric field. We have studied the effect of particle concentration, phi, electric field strength, E(0), and viscosity, eta(m), of the liquid medium on the absorbance-time behavior of the suspensions. Photographs of the electrified suspensions helped in elucidating the structures formed. At low phi values, the absorbance A of electrified suspensions dramatically decreases with time until a constant plateau is reached. The absorbance fall is faster the higher the field, although at long times curves corresponding to different fields tend to merge. In these dilute suspensions particles are observed to migrate toward the electrodes thus clarifying the medium and reducing A. When the concentration of particles is increased, fibrils stretching between the electrodes can be observed in addition to particle deposition on them, as long as the field is kept low. At high fields, migration of the particles to the electrodes occurs whatever the volume fraction. Two mechanisms producing particle-particle interactions are suggested by these data: the conductivity mismatch between the particles and the medium brings about an interfacial or Maxwell-Wagner polarization of the particles; in addition, solids can acquire a net charge provoked by injection from the electrodes. The first mechanism will produce attractive dipole-dipole interactions and hence columns or fibrils. The second one should lead to electrophoretic migration. Structural observations suggest that the latter predominates at high fields. If the viscosity of the fluid phase is increased, the critical electric field values separating both regimes also increase: the electrophoretic motion is hindered and the particle-particle aggregation is enhanced.

Journal Article↗
PubMed2005

Electrical conductivity and stability of concentrated aqueous alumina suspensions.

This work describes the effect of solids load and ionic strength on the electrical conductivity (K(S)) of concentrated aqueous suspensions of commercial alpha-alumina (1-35 vol% solids). The results obtained show that the dependency of the electrical conductivity of the suspending liquid (K(L)) on the volume fraction of solids is well described by Maxwell's model. The change in the conductivity of the suspensions relative to that of the suspending liquid (K(S)/K(L)) was found to be inversely proportional to the solids content, as predicted by Maxwell's model. The relative conductivity rate, DeltaK, could be interpreted in terms of the DLVO theory and the particles double layer parameter, kappaa, and used as a stability criterion. As kappaa changes, in response to the changes in ionic strength, so does the conducting to insulating character of the particles and, as such, their contribution to the overall suspension conductivity (expressed by DeltaK). When the particles become insulating, the suspension conductivity decreases when the solids load increases. The turning point in this particle behaviour corresponds to a critical concentration of ions in the solution that destabilises the suspension and is associated with the critical coagulation concentration (ccc). It is the electrical double layer that ultimately determines the conducting or insulating character of the particles, and that character can be made to change, as required for suspension stability, and accessed by the relative conductivity rate.

Journal Article↗
PubMed2005

Flow properties of freshly prepared ettringite suspensions in water at 25 degrees C.

The rheology of a complex, heterogeneous mineral colloid was rationalised using models devised for model rod systems. Mixing a calcium hydroxide slurry with an aluminium sulphate solution produces a suspension of rod-shaped ettringite particles. Ettringite rod suspensions exhibit non-Newtonian flow behaviour, which depends on the shape of the particles, their size distribution, concentration and surface properties as well as the suspension medium characteristics. We have measured the shear viscosity of suspensions of ettringite rods with a median aspect ratio, r(i) approximately 8, at 25 degrees C as a function of particle volume fraction, phi, in the range 0.0001-0.08. It was found that the viscosity of the suspensions increased with phi, and showed a marked change of slope at phi approximately 0.01, which we identified as the minimum overlap concentration phi(*). Above phi(*), the system is in the semi-dilute regime. At phi>phi(*), when Pe(rot)>1, hydrodynamic interactions between rods become increasingly significant, and we observe shear-thinning behaviour. The high effective hydrodynamic volume of rotating rods, resulting in much lower values of the maximum packing fraction, phi(c), than for spheres, dominates the rheological behaviour of ettringite suspensions.

Journal Article↗
PubMed2005

Rheology and UV protection properties of suspensions of fine titanium dioxides in a silicone oil.

Ultrafine particles of titanium dioxide (TiO2) are very attractive as a UV protection ingredient in cosmetic products. The UV-scattering behavior of TiO2 suspensions in a silicone oil are studied in relation to rheological properties. To control the dispersion stability of suspensions, two types of polyether-modified silicones are used as dispersants. When the suspensions are prepared with branch-type dispersants in which the polyether groups are incorporated as side chains along the backbone, the flow is shear-thinning even at low shear rates. The appearance of plateaus in the frequency-dependence curves of storage modulus implies the solidlike responses. On the other hand, the suspensions prepared with linear conformation dispersants, in which the silicone group and polyether group are alternately repeated in one long chain, are Newtonian at low shear rates. The suspensions are regarded as liquids, because the storage modulus decreases rapidly in the low-frequency region. The suspension rheology is strongly associated with flocculated structures that are primarily controlled by the interparticle attractions. The differences in rheological behavior can be explained by the differences in the adsorbed conformation of dispersant silicones. From optical measurements, it is confirmed that UV scattering increases with decreasing flocculation degree. Therefore, good agreement is established between rheological properties and UV protection ability.

Journal Article↗
PubMed2006

The influence of ionic and nonionic surfactants on aggregative stability and electrical surface properties of aqueous suspensions of titanium dioxide.

The influence of concentration of nonionic TRITON X-100 and anionic ATLAS G-3300 surfactants, and pH of medium on the size and zeta-potential of TiO2 particles in the water suspensions has been studied. Suspensions have been prepared by mixing of the titanium dioxide in the suitable mediums at 10 min and 6 h correspondingly. It was established, that the duration of mixing of the suspensions has an essential influence on the dependence of zeta-potential and size of particles versus concentration of surfactant. However, the duration of mixing does not influence the dependence of electrical conductivity and pH of the suspensions on concentration of surfactant. It is shown that anionic ATLAS G-3300 surfactant is more effective stabilizator of aqueous suspensions of titanium dioxide, than nonionic surfactants of TRITON X-100. It is found that hydrophobic interaction has important role in the processes of stabilization of suspensions for nonionic surfactant, and for anionic surfactant--moving of psi(delta)-planes into solution's depth.

Journal Article↗