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At least 1,387 records · Page 77Linked to original sources
PubMed1980

Estimation of the percentage of free steroid in undiluted serum by centrifugal ultrafiltration-dialysis.

A new method is described for the estimation of the percentages of free steroids in undiluted serum or plasma. Samples were incubated with 3H-steroid and [14C]glucose, and duplicate aliquots of the mixture were subjected to centrifugal ultrafiltration through a dialysis membrane at 37 degrees C. The percentages of free estradiol, testosterone, and progesterone in serum were estimated by comparing the ratio of 3H-steroid to [14C]glucose in the ultrafiltrate with the corresponding ratio in the serum retained by the dialysis membrane. In addition to being highly reproducible, the present method affords several advantages over existing methods. The use of [14C]glucose to monitor the movement of unbound serum components obviates measurement of the ultrafiltrate volume, and because the ultrafiltrate remains in contact with the dialysis membrane, small molecular weight components are able to pass through the dialysis membrane in either direction during centrifugal ultrafiltration. This latter feature, which could be described as "isodialysis," allows the estimation of the percentage of free steroid under conditions which closely approximate the in vivo situation.

Blood Glucose↗
PubMed1978

The effect of sectioning auditory centrifugal fibers on the cochlear microphonic and action potential in guinea pigs.

This investigation on 8 guniea pigs determined the immediate effect on the cochlear microphonic (CM) and action potential (AP) of ipsilateral sectoning of the autitory centrifugal fibers. An acoustic signal was used to evoke the CM and AP of one ear of guinea pig and the homolateral olivo-cochlear bundle and lateral lemniscus were then sectioned. Differences between pre- and post-section CM and AP were measured. The results demonstrated an increase in the CM and a decrease in the AP in all animals. Speculation with regard to the overall function of the auditory centrifugal system was offered.

Action Potentials↗
PubMed1993

[Comparative analysis of various plasmapheresis methods--modern procedures of mechanical plasma collection compared with each other and with manual bag centrifugation procedures].

Four plasmapheresis procedures (manual blood bag centrifugation plasmapheresis, and the three plasmapheresis machines P.C.S./Haemonetics, Autopheresis-C/Baxter-Travenol, Plasmapur Monitor/Organon Teknika) were studied comparatively. The three machine procedures could be performed more easily and more rapidly and were well accepted by donors, autologous donors (patients) and staff. Compared with the traditional, well established manual procedure, a possible impairment of the plasma donors seems reduced rather than raised. Activation of the hemostatic system of the donors, measured with very sensitive methods, was found to be less pronounced when plasmapheresis was performed with the machines than when it was performed conventionally. The plasma product obtained by machine plasmapheresis was found to be of higher quality. All three systems showed less activation of the clotting system. Especially the plasma obtained by the P.C.S. showed a higher clotting factor yield. Plasma obtained by the Autopheresis-C and by the Plasmapur Monitor (both systems are equipped with filters) was markedly less contaminated with cells. The recently found low activation of the clotting system of plasma recipients, however, showed no differences when plasma obtained conventionally or by the Plasmapur Monitor was used. In summary, the new machine plasmapheresis devices offer a good alternative to the conventional blood bag centrifugation method and set new standards for the production of high quality plasma.

Blood Coagulation Tests↗
PubMedDate not supplied

Flow visualization evaluation of secondary flow in a centrifugal blood pump.

To design a less hemolytic and more antithrombogenic centrifugal blood pump, secondary flow, i.e., vortex and turbulent flow, must be properly controlled. An irregular stream pattern is a cause of hemolysis, and good wash-out around the shaft minimizes thrombus formation. In this study, flow visualization methods were applied to evaluate secondary flow in a centrifugal blood pump. Correlation with results of in vitro hemolysis tests was investigated. Separation of the stream lines from the vanes and patterns implying the existence of vortices were observed in the impeller that showed high hemolysis. By adjustment of vane angles, these irregular patterns could be minimized, and hemolysis decreased as well. Using a similar technique, the flow pattern at the back of the impeller could be visualized, which enabled further investigation of the effects of secondary flow on thrombus formation. This flow visualization was effective in examining secondary flow patterns.

Animals↗
PubMed1977

[Centrifugal annular erythema of Colcott-Fox type (erythema gyratum perstans)].

The case of a child with Colcott-Fox type of centrifugal annular chronic erythema is reported. It is a sporadic, non-familial form, associated with a bullous eruption, and an atrophic conjonctivitis with trichiasis. A review is made of 11 previously published cases, allowing a synthesis of their essential features. The action played by the slow reactive substances (S. R. S. A.) in the extension of the erythematous margin is discussed. The clinical diagnosis of centrifugal annular erythema is exposed.

Child, Preschool↗
PubMed1996

Characteristics of a blood pump combining the centrifugal and axial pumping principles: the spiral pump.

Two well-known centrifugal and axial pumping principles are used simultaneously in a new blood pump design. Inside the pump housing is a spiral impeller, a conically shaped structure with threads on the surface. The worm gears provide an axial motion of the blood column through the threads of the central cone. The rotational motion of the conical shape generates the centrifugal pumping effect and improves the efficiency of the pump without increasing hemolysis. The hydrodynamic performance of the pump was examined with a 40% glycerin-water solution at several rotation speeds. The gap between the housing and the top of the thread is a very important factor: when the gap increases, the hydrodynamic performance decreases. To determine the optimum gap, several in vitro hemolysis tests were performed with different gaps using bovine blood in a closed circuit loop under two conditions. The first simulated condition was a left ventricular assist device (LVAD) with a flow rate of 5 L/min against a pressure head of 100 mm Hg, and the second was a cardiopulmonary bypass (CPB) simulation with a flow rate of 5 L/min against 350 mm Hg of pressure. The best hemolysis results were seen at a gap of 1.5 mm with the normalized index of hemolysis (NIH) of 0.0063 +/- 0.0020 g/100 L and 0.0251 +/- 0.0124 g/100 L (mean +/- SD; n = 4) for LVAD and CPB conditions, respectively.

Animals↗
PubMed1962

Electron microscopy of lysosome-rich fractions from rat thymus isolated by density-gradient centrifugation before and after whole-body x-irradiation.

Fractions from rat thymuses were isolated by sucrose density-gradient centrifugation, before and after 1000 r whole-body x-irradiation, and examined by electron microscopy. Cytochrome oxidase and acid phosphatase activities of these fractions were tested as well. Electron-opaque bodies with diameters ranging from 0.10 to 0.35 micro, with a mean of 0.25 micro, were found in fractions having high acid phosphatase activity, while the fractions rich in cytochrome oxidase consisted mostly of mitochondria. After irradiation, there was an increased ratio of dense bodies to mitochondria. These particles are considered to be lysosomes similar to those identified in other rat tissues. Their relationship to the mitochondria is discussed.

Animals↗
PubMed1964

DENSITY GRADIENT CENTRIFUGATION OF A MURINE LEUKEMIA VIRUS.

The Rauscher leukemia virus separated as a single band upon density gradient centrifugation in cesium chloride, rubidium chloride, sucrose, potassium citrate, or potassium tartrate. Prolonged exposure to concentrated potassium citrate or potassium tartrate solutions caused lysis of the virus; the resulting products, having different densities, separated on the density gradients.

Animals↗
PubMed1987

Purification of Cowdria ruminantium by density gradient centrifugation.

The isolation of Cowdria ruminantium by differential and isopycnic density gradient centrifugation is reviewed with special reference to the suitability of Percoll as density gradient medium. Infected sheep brain, Amblyomma hebraeum nymphae and various mouse organs were used as starting material. By these methods, partially purified viable populations of the organism with distinctly different densities were obtained. The conclusions are based upon results of analyses of density fractions by inoculation into sheep or mice, protein determination, electron microscopy and enzyme-linked immunosorbent assay. Morphological differences were observed in the density fractions obtained from infected brain tissue and A. hebraeum.

Animals↗
PubMed1983

Isopycnic density-gradient centrifugation: a separation parameter which improves flow cytometric measurements on heterogeneous tumors.

The analytic and prognostic value of flow cytometric measurements can generally be improved by preseparation of cells. The present data demonstrate clearly the distinct character of bands obtained in density-gradient separation. Density-gradient centrifugation in Percoll after extensive Ca2+ + Mg2+ elimination helps to resolve more detail in flow cytometric measurements (e.g., additional DNA stem lines in human tumors) and can be used in studies of tumor heterogeneity. The significance of investigations of tumor heterogeneity is demonstrated by the different reactivity of subpopulations of the experimental murine tumor S 180 to vincristine.

Animals↗
PubMed1987

Linear Percoll gradient centrifugation of rat anterior pituitary cells. A simple method for prolactin cell enrichment.

Prolactin (PRL) cells were purified from nulliparous normal female adult Wistar rat pituitary cell suspensions by linear Percoll density gradient centrifugation, a procedure yielding single cells. Lactotrophs were found in two different layers, the first containing 70% PRL cells in the density range 1.055 to 1.065 g/ml, the second with 28% PRL cells in the range 1.070 to 1.080 g/ml. Both cell fractions contained more than 90% viable cells with an intact ultrastructure. The physiological integrity of the 70% enriched PRL cells was assessed by their basal PRL secretion, their secretory response to TRH and dopamine, and their cAMP production in a basal situation and after incubation with dopamine.

Animals↗
PubMed1977

Characterization of gastric mucosal membranes. IX. Fractionation and purification of K+-ATPase-containing vesicles by zonal centrifugation and free-flow electrophoresis technique.

Methods are described for purification of a vesicular membrane fraction of hog gastric mucosa using differential centrifugation, density gradient separation on zonal rotors and free-flow electrophoresis. As a result a fraction is obtained enriched 40-fold in terms of K(+)-ATPase and free of any other enzyme marker other than K(+)-activated p-nitrophenyl phosphatase. The 5'-nucleotidase and basal Mg(2+)-ATPase are clearly separated from the latter enzymes. Osmotic shock, Triton X-100 treatment or K+ ionophores increased the K(+)-ATPase activity in isotonic conditions, but K(+)-p-nitrophenyl phosphatase is not affected by these treatments, nor is the ATPase activity in the presence of NH4+. The results suggest that the electrophoretic fraction contains a major population of tight vesicles, whose permeability to K+ is rate limiting for the ATPase activity but not for the p-nitrophenyl phosphatase activity. It is concluded that K+ site for the ATPase is internal whereas the K+ site for the p-nitrophenyl phosphatase is external, hence, the K+ site must be mobile across the membrane.

4-Nitrophenylphosphatase↗
PubMed1979

A new gradient former and a simplified procedure for zonal centrifugation of immune complexes.

A new gradient former for production of optimized sucrose gradients for B-XIV zonal rotors is described. Optimized gradients are gradients with an initial shelf to provide capacity and a shape that ensures isokinetic sedimentation conditions. By exhaustive computer calculations it has been found that optimized gradients can be produced by a very simple two-compartment gradient former. The design is given. Moreover, graphs for choice of gradient strength and run duration for preparative and analytical runs of samples containing soluble immune complexes are calculated. The new gradient former allows the use of a very simple procedure for zonal centrifugation.

Antigen-Antibody Complex↗
PubMed1985

Isolation of bacterial plasmids by density gradient centrifugation in cesium trifluoroacetate (CsTFA) without the use of ethidium bromide.

Plasmids extracted from bacterial cells by alkaline extraction can easily be isolated from linear DNA by isopycnic centrifugation in CsTFA. This is a fast and simple method which circumvents the use of the intercalating dye, ethidium bromide, and consequently the problems associated with its removal. The buoyant densities for covalently closed circular DNA and linear DNA in CsTFA are 1.60 g/ml and 1.65 g/ml, respectively. The isolation is achieved regardless of plasmid size and can be accomplished at temperatures of between 4 and 30 degrees C. Plasmid DNA isolated in gradients of CsTFA are of a high purity and have been found to be intact when cleaved with restriction enzymes and ligated with T4 DNA ligase.

Centrifugation, Density Gradient↗
PubMed1969

A study of nucleated erythrocytes by density-gradient centrifugation in a zonal rotor.

1. Several substances of high molecular weight were examined for their suitability as suspension media in the formation of density gradients for the zonal centrifugation of avian erythrocytes. None proved satisfactory. 2. The behaviour of pigeon erythrocytes in rate-sedimentation experiments in a type A zonal rotor with density gradients of sucrose was examined. The mature cells sediment more rapidly than the younger cells and have a lower RNA/DNA ratio. Maturation is accompanied by a greater loss of RNA from the nucleus than from the cytoplasm. 3. The base composition of the nuclear RNA and of the two species of cytoplasmic ribosomal RNA is reported. 4. The RNA of erythrocytes may be labelled in vivo by injection of inorganic [(32)P]phosphate. The cells most active in the synthesis of RNA sediment less rapidly than the bulk of the cells. 5. Reticulocyte nuclei sediment more slowly than those from erythrocytes. Reticulocyte nuclei have a mean volume of 35mu(3) and are isopycnic with sucrose of density 1.2871 (measured at 20 degrees ). Maturation of the nuclei causes them to shrink to a volume of 25mu(3) and the density to increase to 1.2944.

Animals↗
PubMed1979

Tissue-culture cell fractionation. Fractionation of cellular membranes from 125I/lactoperoxidase-labelled Lettrée cells homogenized by bicarbonate-induced lysis: resolution of membranes by zonal centrifugation and in sucrose and metrizamide gradients.

1. Lettrée cells were grown intraperitoneally in MF-1 mice and labelled extrinsically by the 125I/lactoperoxidase technique. 2. The cells were swollen in 1 mM-NaHCO3 and disrupted in a Dounce homogenizer. 3. Crude fractions of endoplasmic reticulum, plasma membrane and mitochondria were separated from a post-nuclear supernatant by sedimentation-rate gradient centrifugation in a BXIV zonal rotor. 4. Further resolution of these membranes was carried out in isopycnic sucrose gradients. 5. Bands of material from the latter were subfractionated in gradients of metrizamide. Some very pure subfractions of plasma membrane and endoplasmic reticulum were obtained. In addition, one subfraction containing 125I and NADPH-cytochrome c reductase but no Na++K+-stimulated adenosine triphosphatase and another containing these two enzymes but no 125I were resolved.

Animals↗
PubMed1980

The comparative diagnostic accuracy of cancer-cell detection obtained with Ficoll-Hypaque gradient separation and standard centrifugation technics on body-cavity fluids.

Ninety-two consecutive samples of body-cavity fluids from patients with confirmed or suspected cancer were compared for accuracy of diagnosis using a Ficoll gradient test and a standard centrifugation test. The percentage of positive test results was 76% (70/92) with the Ficoll test and 64% (59/92) with the routine test. The Ficoll and routine tests also gave a significant difference in the classification of malignancy, with the latter test giving a significantly higher proportion of negative or inconclusive test results. Besides the improved test results, the Ficoll gradient test has the further advantages of being less expensive and requiring only standard laboratory equipment. Elimination of blood and cellular debris by the procedure results in quick and easy cytologic screening. The Ficoll test is strongly recommended for those clinical fluids suspected to be positive for malignancy, especially where the routine test is negative or inconclusive.

Body Fluids↗
PubMed1983

The cell cycle of the budding yeast Sterigmatomyces halophilus: culture fractionation by zonal centrifugation and the accumulation of DNA, RNA and protein.

Sterigmatomyces halophilus is an unusual budding yeast in which daughter cells are formed, remote from the mother cell, on fine projections called sterigmata. Some fundamental properties of the cell cycle have been explored by separating cells from an exponentially growing culture into size, and thus age, classes by density-gradient centrifugation. Rate separations on high capacity, high resolution, equivolumetric gradients of sucrose, or, alternatively, isopycnic separations on gradients of Urografin revealed consistent and reproducible patterns of accumulation of DNA, RNA and protein through the cell cycle. Total DNA accumulation was stepwise, synthesis occurring late in the cycle, whilst protein accumulated continuously with no evidence for the discontinuities reported in some other lower eukaryotes. Total RNA accumulation, measured either colorimetrically or by long-term incorporation of radioactively-labelled uracil was transiently elevated early in the cycle and then accumulated continuously. A mathematical analysis of the volume distributions of the cells in fractions from the gradients showed that there is a hyperbolic relationship between cell age and size but that, to a first approximation, measurements of cell size (and density) are direct measures of age. The results are discussed with reference to (1) the unusually high buoyant density of this yeast, (2) the resolution of zonal cell separation methods and (3) macromolecular accumulation in the cell cycles of other eukaryotic micro-organisms.

Cell Cycle↗