Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Polyethylene”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50Linked to original sources
PubMed1987

Polyethylene glycol-induced heteroassociation of malate dehydrogenase and citrate synthase.

Studies by dynamic and total intensity light scattering, ultracentrifugation, electron microscopy, and chemical crosslinking on solutions of the pig heart mitochondrial enzymes, malate dehydrogenase and citrate synthase (separately and together) demonstrate that polyethylene glycol induces very large homoassociations of each enzyme, and still larger heteroenzyme complexes between these two enzymes in the solution phase. Specificity of this heteroassociation is indicated by the facts that heteroassociations with bovine serum albumin were not observed for either the mitochondrial dehydrogenase or the synthase or between cytosolic malate dehydrogenase and citrate synthase. The weight fraction of the enzymes in the mitochondrial dehydrogenase-synthase associated particles in the solution phase was less than 0.03% with the dilute conditions used in the dynamic light scattering measurements. Neither palmitoyl-CoA nor other solution conditions tested significantly increased this weight fraction of associated enzymes in the solution phase. Because of the extremely low solubility of the associated species, however, the majority of the enzymes can be precipitated as the heteroenzyme complex. This precipitation is a classical first-order transition in spite of the large particle sizes and broad size distribution. Ionic effects on the solubility of the heteroenzyme complex appear to be of general electrostatic nature. Polyethylene glycol was found to be more potent in precipitating this complex than dextrans, polyvinylpyrrolidones, ficoll, and beta-lactoglobulin.

Animals↗
PubMed1992

Subunit interactions of Rubisco activase: polyethylene glycol promotes self-association, stimulates ATPase and activation activities, and enhances interactions with Rubisco.

The effect of polyethylene glycol (PEG) on the enzymatic and physical properties of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase was examined. In the presence of PEG, Rubisco activase exhibited higher ATPase and Rubisco activating activities, concomitant with increased apparent affinity for ATP and Rubisco. Specific ATPase activity, which was dependent on Rubisco activase concentration, was also higher in the presence of Ficoll, polyvinylpyrrolidone, and bovine serum albumin. The ability of Rubisco activase to facilitate dissociation of the tight-binding inhibitor 2-carboxyarabinitol 1-phosphate from carbamylated Rubisco was also enhanced in the presence of PEG. Mixing experiments with Rubisco activase from two different sources showed that tobacco Rubisco activase, which exhibited little activation of spinach Rubisco by itself, was inhibitory when included with spinach Rubisco activase. Polyethylene glycol improved the ability of tobacco and a mixture of tobacco plus spinach Rubisco activase to activate spinach Rubisco. Estimates based on rate zonal sedimentation and gel-filtration chromatography indicated that the apparent molecular mass of Rubisco activase was two- to fourfold higher in the presence of PEG. The increase in apparent molecular mass was consistent with the propensity of solvent-excluding reagents like PEG to promote self-association of proteins. Likewise, the change in enzymatic properties of Rubisco activase in the presence of PEG and the dependence of specific activity on protein concentration resembled changes that often accompany self-association. For Rubisco activase, high concentrations of protein in the chloroplast stroma would provide an environment conducive to self-association and cause expression of properties that would enhance its ability to function efficiently in vivo.

Adenosine Triphosphatases↗
PubMed1977

Liquid-phase method for peptide synthesis utilizing photolytic cleavage from a new o-nitrobenzoyl polyethylene glycol support.

Photolysis as a method for removal of a tert-butyloxycarbonyl-protected peptide possessing a free C-terminal carboxyl group from a polystyrene support in the solid-phase method of peptide synthesis was introduced by Rich, D. H. and Gurwara, S. K.((1975) J. Am. Chem. Soc. 97, 1575-1578). Using this basic concept we prepared a photosensitive 3-nitro-4-bromomethylbenzoyl polyethylene glycol support for use in the liquid-phase method of peptide synthesis. Photolytic cleavage of a protected tetrapeptide possessing a free C-terminal carboxyl group from the polyethylene glycol support resulted in a 98% yield compared with a 69% yield for the photolytic leavage from the polystyrene support. This application of photolysis as a cleavage method in liquid-phase peptide synthesis avoids the low yields and rather drastic conditons needed to remove a peptide attached directly to the poly-ethylene glycol support in the conventional liquid-phase method.

Alanine↗
PubMed1983

A new micromethod for the quantification of low molecular weight oligomers of polyethylene glycol.

We describe a gas-liquid chromatographic technique for quantifying the low molecular weight (Mr 106-634) oligomers of polyethylene glycol (PEG) in clinical specimens. The deionized sample, containing tetra-ethylene glycol as an internal standard, is applied on column. This technique readily quantifies as little as 2.5 micrograms of an individual oligomer; with such a quantity, the coefficient of variation is +/- 2.5 percent (N = 25 analyses). Small volumes (250 microliter) of urine are conveniently analyzed, and a single column can be utilized for the analysis of approximately three hundred specimens. We have analyzed timed urine specimens from humans who received 0.15 g of PEG 400 per kilogram. Individuals varied markedly with regard to the total amount of PEG excreted into the urine; each subject, however, consistently excretes a uniform percentage of the ingested dose. The urinary oligomeric profile of PEG does not vary from subject to subject nor from hour to hour, during the first six hours following oral administration, so that a random urine obtained during this period provides a reliable clinical specimen. This technique should facilitate clinical studies that utilize polyethylene glycol 400 as an index of passive intestinal transport.

Adult↗
PubMed1979

Comparison of segmented polyether urethane with polyethylene IUDs in rabbits.

A segmented polyether urethane IUD was compared with a polyethylene IUD in rabbits. The contraceptive efficacy of urethane IUDs was excellent. Moreover, the purulent slippery deposit present with the polyethylene IUDs and observed by Davis et al. (1) was absent. Our studies indicate that the polyether urethane IUDs have a high degree of antifertility activity in rabbits and these IUDs have reduced inflammatory response, based on leucocytic infiltration and tissue debris in the uterine lumen. It is suggested that polyether urethane IUDs not requiring copper or other medication can be designed for high contraceptive efficacy, intrauterine compatibility and with the necessary rigidity for proper uterine retention in humans.

Animals↗
PubMed1985

Effect of polyethylene glycol on the kinetic behaviour of pyruvate kinase and other potentially regulatory liver enzymes.

Assay in the presence of 10% polyethylene glycol has been systematically used with potentially regulatory liver enzymes as an indirect way to induce aggregation of enzymes corresponding to that which could occur at their physiological concentrations. Pyruvate kinase L was markedly affected by polyethylene glycol, as was muscle phosphorylase a, while pyruvate kinase M as well as glucokinase, fructose-1,6-bisphosphatase and other liver enzymes examined were not affected.

Adenosine Triphosphate↗
PubMed1987

Treatment of vitamin E deficiency during chronic childhood cholestasis with oral d-alpha-tocopheryl polyethylene glycol-1000 succinate.

Treatment of vitamin E deficiency during chronic childhood cholestasis is hampered by the poor intestinal absorption of available oral preparations of vitamin E when bile flow is severely impaired; thus parenteral vitamin E has been the only effective therapy for many children with this problem. We studied the intestinal absorption, efficacy, and safety of a water-soluble oral form of vitamin E, d-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS), in 22 children (7 mo to 19 yr old) with severe cholestasis and vitamin E deficiency who were unresponsive to massive oral doses (100-200 IU/kg.day) of dl-alpha-tocopherol. The results of oral vitamin E tolerance tests showed that TPGS was well absorbed in virtually all study subjects, that TPGS intestinal absorption was superior to that of dl-alpha-tocopherol, and that TPGS absorption in teenage children with chronic cholestasis was similar to that of normal adults. In addition, 1.7% +/- 1.6% (mean +/- SD) of the administered polyethylene glycol 1000 contained in the TPGS was absorbed and excreted in the urine of the 13 subjects analyzed, compared with 3.0% +/- 1.3% in 4 normal adults. A chronic oral dose of 15-25 IU/kg.day of TPGS corrected the biochemical vitamin E deficiency state over 1-19 mo (mean, 10.6 mo) of TPGS therapy. No clinical or biochemical evidence of gastrointestinal, renal, hepatic, or hematologic toxicity was demonstrated. This study suggests that TPGS administered orally in a dose of 15-25 IU/kg.day may be a safe and effective form of vitamin E for prevention and correction of vitamin E deficiency during severe childhood cholestasis.

Administration, Oral↗
PubMed1989

Mechanisms of polyethylene glycol 400 permeability of perfused rat intestine.

Abnormal permeability to polyethylene glycol 400 (PEG 400) has been demonstrated in various disorders with defective intestinal barrier functions. To understand the basic mechanisms of PEG 400 permeability, we compared PEG 400 permeation in different segments of the intestine and studied the kinetics and influence of intraluminal factors on PEG 400 absorption in vivo in perfused intestinal segments of the rat. The permeation rate of PEG 400 was dependent on the luminal concentration (y = 12.99x + 3.5; r = 0.97), indicating that passive movement is the mechanism involved in PEG 400 absorption. Changing the perfusate pH from 6 to 7.4 or modifying the unstirred water layer resistance by changing luminal flow rate did not affect PEG 400 absorption. When luminal osmolarity was varied from 0.225 to 0.6 osmol/L, higher osmolarity decreased both water and PEG 400 absorption (p greater than 0.01). The relationship between PEG 400 and water absorption at different osmolarities was linear (y = 0.9x + 5.7; r = 0.98). At a luminal osmolarity of 0.3 osmol/L 43% of PEG 400 permeation was mediated by passive diffusion and 57% was mediated by solvent drag. Increasing water absorption by decreasing luminal osmolarity resulted in proportional increase of PEG 400 permeation through solvent drag or convection. The solvent drag reflection coefficient (sigma f) for PEG 400 permeation of the jejunum was 0.1. Taurocholic acid (10 mM) alone or with oleic acid (2.5 mM) did not affect PEG 400 absorption. Permeabilities of 1 mM PEG 400 and water were similar in jejunum and ileum but were markedly increased in the colon (p greater than 0.01). These studies demonstrate that PEG 400 is absorbed by both passive diffusion and by solvent drag, with the latter accounting for a greater fraction of the absorptive drive under normal conditions. Polyethylene glycol 400 uses aqueous pathways for its permeation across the intestinal epithelium.

Animals↗
PubMed1996

A sliding-distance-coupled finite element formulation for polyethylene wear in total hip arthroplasty.

A three-dimensional, nonlinear contact finite element (FE) model of total hip replacement, linked to a sliding-distance-coupled wear algorithm, was used to study polyethylene wear rates for three different femoral head sizes. Hip resultant loads from a validated gait analysis model were used in the FE model to determine contact stress distributions on the polyethylene bearing surface, for 16 discrete instants of stance phase. Sliding distances of points on the femoral head surface were obtained from the corresponding flexion/extension kinematics. Wear rates were determined by a custom-written computer program that used a relationship that coupled contact stress, sliding distance, and a pin-on-disk determined wear coefficient. The wear rates computed by this formulation were well within clinically observed ranges for each component size.

Algorithms↗
PubMed1981

Cell surface fixation of alloantigen bearing plasma vesicles in the presence of polyethylene glycol.

The fixation of plasma vesicles at the surface of intact mouse spleen or tumor cells was studied in order to introduce the foreign alloantigens of the vesicles into the plasma membrane of these cells. A 3-6-fold increase of fixation of radioiodinated vesicles was obtained when cells and vesicles were incubated in the presence of polyethylene glycol 1500 (PEG 1500). The fixation of vesicles on the surface of cells was demonstrated by scanning electron microscopy. Cells treated with vesicles in the presence of PEG acquired the corresponding membrane alloantigens, as demonstrated by cellular binding radioimmunoassay. However, sensitivity to antibody-dependent lysis was obtained only when vesicle fixation was achieved in the presence of both wheat germ agglutinin and polyethylene glycol. The introduction of foreign alloantigens in the plasma membrane of the treated cells might help to define the functional properties of these molecules.

Animals↗
PubMed1983

A quantitative examination of the light scattering properties of immune complexes in polyethylene glycol.

The effect of polyethylene glycol on the light scattering properties of immune complexes prepared in vitro was examined. Immune complexes were prepared in the zone of antigen excess from purified rabbit anti-ovalbumin and ovalbumin at 2-32 times (X) the equivalence ratio. Immune complex concentration was determined by analytical ultracentrifugation. Immune complexes were then incubated for 1 h in solutions containing 0, 1, 2, 3 and 4% polyethylene glycol (PEG), and examined in a laser nephelometer. The effect of PEG on light scattering (%RLS) was different for each immune complex combining ratio, although for each immune complex combining ratio, there was a linear relationship between the light scattered and immune complex concentration. To evaluate the effect of serum proteins on the light scattered by the immune complexes, immune complexes made at 4X and 16X the equivalence ratio were placed in serum and the sera containing these immune complexes were examined in the nephelometer. The ratio of the %RLS of the immune complexes in serum to the sum of the %RLS of the same immune complexes in saline plus the %RLS of serum alone was determined. This ratio varied systematically with changes in combining ratio and PEG concentration, as well as the concentration of the immune complexes themselves. Depending on the combination of these 3 factors, serum could increase, decrease or have no effect on the quantity of light scattered by the immune complexes. Discrimination between serum alone and serum containing immune complexes was best in 3% PEG.

Animals↗
PubMed1992

The transverse strengths of three denture base resins reinforced with polyethylene fibers.

This investigation compared the transverse strengths of three denture base resins with and without polyethylene reinforcement fibers. These fibers were incorporated in 10 specimens each of a high-impact strength resin, a rapid heat-polymerized resin, and a light-activated resin. Each specimen was broken on an Instron universal testing machine using a three-point load after processing and air drying. The values obtained were then compared with values previously recorded for the same type of specimens without incorporated fibers. Only the light-activated denture base resin specimens exhibited a significantly higher mean transverse strength after polyethylene fiber reinforcement.

Acrylic Resins↗
PubMed1994

Effect of polyethylene fiber reinforcement on the strength of denture base resins polymerized by microwave energy.

This study investigated the effect of addition of polyethylene fibers on the transverse strength, deflection, and elastic modulus of two denture base acrylic resins polymerized by microwave irradiation. Specimens of each resin, Lucitone 199 and Acron MC, were fabricated with 0.0%, 0.5%, 1.5%, and 3.0% fiber loading. Specimens were tested with use of a three-point flexure apparatus with an Instron universal testing machine after storage in water for 10 days at 37 degrees C. The results showed that polyethylene fibers significantly decreased the transverse strength of Acron MC resin and slightly increased the transverse strength of Lucitone 199 resin at a loading of 0.5% by weight. Fiber loading did not significantly affect the deflection and the elastic modulus of either material.

Acrylic Resins↗
PubMed1977

Polyethylene tubes as a model for the root canal.

Polyethylene tubes, closed at both ends with casting wax and with four perforations in the middle, were implanted subcutaneously in rats and evaluated as a research model simulating the root canal. As controls, wax bars and unperforated tubes were implanted. Attention was given to the reaction of the tissue surrounding the perforated empty tube, the tissue reaction to polyethylene and casting wax, and to the displacement of the tubes.

Animals↗
PubMed1979

The effects of overfilled polyethylene tube intraosseous implants in rats.

Polyethylene tubes obturated flush at one end overfilled 2 mm. at the opposite end with unset Grossman's cement and gutta-percha were implanted in rat tibias. Microscopic evaluation of the specimens revealed that (1) the gutta-percha, Grossman's sealer, and polyethylene tubing are well tolerated by rat intraosseous tissue and (2) a canal overextended 2 mm. beyond the apex with Grossman's cement and gutta-percha produces an early mild to moderate inflammatory response which resolves by the end of 30 day's. The overfillings did not significantly compromise the healing of rat intraosseous tissue.

Animals↗
PubMed1992

Restoration of immunoglobulin secretion in vitro in common variable immunodeficiency by in vivo treatment with polyethylene glycol-conjugated human recombinant interleukin-2.

Patients with common variable immunodeficiency (CVI) have decreased immunoglobulin levels resulting in frequent infections. Although previous studies have suggested that the B cell is intrinsically defective, numerous T cell deficiencies, including reduced interleukin-2 (IL-2) production, have been described. Since the addition of T cell cytokines to CVI B cells can increase Ig secretion in vitro, hypogammaglobulinemia in CVI may be due to defective T cell functions. To assess this possibility directly, we treated five CVI patients intravenously with a new biologic, human recombinant IL-2 conjugated to polyethylene glycol. Doses were 250,000 IU/m2 weekly for Weeks 1-4, 500,000 IU/m2 for Weeks 5-8, and 10(6) IU/m2 for Weeks 9-12. During and after treatment, B cells of all patients secreted 10- to 1000-fold more Ig in vitro. There was also a striking improvement in T cell helper activity since T cells of treated patients could induce 10- to 10,000-fold increases in Ig secretion by B cells from normal donors. No increase was seen in serum Igs during the study, but the anti-tetanus antibody of the IgG isotype could be detected in cell culture supernatants. Whether the effects of infused polyethylene glycol IL-2 are mediated through T or B cells, or both, is still unknown. However, these data reinforce the concept that CVI B cells may be competent, but, lacking essential T cell growth factors, in vivo maturation to Ig production does not occur.

Adult↗
PubMed1984

The intra-articular response to particulate carbon fibre reinforced high density polyethylene and its constituents: an experimental study in mice.

Carbon fibre reinforced high density polyethylene (CFRHDP) Meuller acetabular cups are available for total hip replacement. Despite the improved mechanical properties of CFRHDP over high density polyethylene (HDP) the wear characteristics of CFRHDP are a contentious issue. The biocompatibility of CFRHDP wear debris was investigated by intra-articular injection into mice and compared with that induced by HDP and carbon fibres. The response to CFRHDP was identical to that seen with HDP: the carbon fibre component did not appear to modify the response. From the biological point of view, therefore, the wear properties of CFRHDP must be better than those of HDP to offer a significant advantage.

Animals↗
PubMed1984

Effect of steam sterilization on polyethylene terephthalate.

Subtle changes on the surface of polymeric materials on autoclaving have been ignored so far. An increase in cyclic trimer content on the surface of polyethylene terephthalate on autoclaving is reported. This increase may affect the biocompatibility of polyethylene terephthalate. Quantification of the cyclic trimer was done by high performance liquid chromatography.

Biocompatible Materials↗