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Biomedical subjects

E Evans

Publications and source records attributed to E Evans.

At least 109 records · Page 6Linked to original sources
PubMed1985

Difficulties in the endoscopic diagnosis of gastric and oesophageal cancer.

A study was made of 116 patients with gastric or oesophageal cancer, in whom endoscopy was negative, or biopsy was negative or not performed. The most common problems were the presence of pyloric or oesophageal stricture (sometimes with excessive luminal content) and difficulty in obtaining diagnostic biopsy material in linitis plastica, early gastric cancer, lymphoma and sarcoma. Problems also occurred from failure to biopsy apparently benign conditions and from delay in a second endoscopy. Some cancers were regarded as benign ulcers and treated as such by drugs or surgery because more reliance was placed on endoscopic biopsy than on the endoscopist's opinion of the macroscopic appearance. In 17 of the 16 patients there was delay, incorrect management or further difficulty in diagnosis.

Diagnostic Errors↗
PubMed1985

Morbidity and mortality of operative intubation for malignant oesophageal obstruction.

In 33 patients who underwent operative intubation of carcinoma of the oesophagus or gastric cardia, there were nine postoperative deaths (mortality 27%). Only 15 patients (46%) had no further operative procedure or anaesthetics, but their mean survival was only 3.7 months. Nine patients (27%) required a total of 17 procedures after the placement of their original tube. Operative intubation has a similar mortality to resection but the survival times are short. Whenever possible palliative resection or endoscopic intubation is to be recommended.

Aged↗
PubMed1985

Sickle erythrocyte adherence to vascular endothelium. Morphologic correlates and the requirement for divalent cations and collagen-binding plasma proteins.

Increased adherence of sickle erythrocytes to vascular endothelium has been suggested by Hebbel and his colleagues to play a role in vasocclusive events of sickle cell disease. To define the role of cell membrane changes and plasma factors in cell adherence, a micropipette technique previously developed by us to obtain a direct, quantitative measure of cell adherence was used to evaluate the adhesivity of different morphologic classes of sickle cells to endothelial cells in various suspending media. Irregularly shaped, deformable sickle cells were four- to fivefold more adherent than discoid sickle cells, whereas rigid irreversibly sickled cells were least adherent. Sickle erythrocytes adhered to endothelial cells when suspended in autologous citrated or heparinized plasma but were totally nonadherent when suspended in autologous EDTA plasma. Removal of the divalent cation chelator and addition of calcium to EDTA plasma restored its ability to promote adhesion, implying an absolute requirement for divalent cations in sickle cell adherence. Sickle cells also did not adhere to endothelial cells in protein-free media containing divalent cations, suggesting an additional requirement for plasma proteins. Removal of collagen-binding proteins from citrated sickle plasma resulted in a three- to fivefold reduction in its ability to promote cell adhesion, suggesting an important role for these plasma proteins in sickle cell adherence. The results of this study imply that sickle cell adherence to vascular endothelium is a complex process in which temporal changes in the numbers of cells identified to be most adhesive and the plasma concentration of protein(s) involved in the adhesive process determine the extent of in vivo sickle cell adherence.

Anemia, Sickle Cell↗
PubMed1984

Free energy potential for aggregation of giant, neutral lipid bilayer vesicles by Van der Waals attraction.

Here, we report the first direct observation of Van der Waals' attraction between biomembrane capsules using measurements of the free energy reduction per unit area of membrane-membrane contact formation. In these studies, the membrane capsules were reconstituted neutral (egg phosphatidylcholine) lipid bilayers of giant (greater than 10(-3) cm diam) vesicles. Micromanipulation methods were used to select and maneuver two vesicles into proximity for contact; after adhesion was allowed to occur, the extent of contact formation was regulated through the vesicle membrane tensions that were controlled by micropipette suction. The free energy reduction per unit area of contact formation was proportional to the membrane tension multiplied by a simple function of the pipette and vesicle dimensions. The free energy potential for Van der Waals attraction between the neutral bilayers in 120 mM NaCl solutions was 1.5 X 10(-2) ergs/cm2. Also, when human serum albumin was added to the medium in the range of 0-1 mg/ml, the free energy potential for bilayer-bilayer adhesion was not affected. Using published values for equilibrium spacing between lipid bilayers in multilamellar lipid-water dispersions and the theoretical equation for van der Waals attraction between continuous dielectric layers, we calculated the value for the Hamaker coefficient of the Van der Waals attraction to be 5.8 X 10(-14) ergs.

Cell Aggregation↗
PubMed1984

Free energy potential for aggregation of mixed phosphatidylcholine/phosphatidylserine lipid vesicles in glucose polymer (dextran) solutions.

The energetics of lipid vesicle-vesicle aggregation in dextran (36,000 mol wt) solutions have been studied with the use of micromechanical experiments. The affinities (free energy reduction per unit area of contact) for vesicle-vesicle aggregation were determined from measurements of the tension induced in an initially flaccid vesicle membrane as it adhered to another vesicle. The experiments involved controlled aggregation of single vesicles by the following procedure: two giant (approximately 20 micron diam) vesicles were selected from a chamber on the microscope stage that contained the vesicle suspension and transferred to a second chamber that contained a dextran (36,000 mol wt) salt solution (120 mM); the vesicles were then maneuvered into position for contact. One vesicle was aspirated with sufficient suction pressure to create a rigid sphere outside the pipette; the other vesicle was allowed to spread over the rigid vesicle surface. The aggregation potential (affinity) was derived from the membrane tension vs. contact area. Vesicles were formed from mixture of egg lecithin (PC) and phosphatidylserine (PS). For vesicles with a PC/PS ratio of 10:1, the affinity showed a linear increase with concentration of dextran; the values were on the order of 10(-1) ergs/cm2 at 10% by weight in grams. Similarly, pure PC vesicle aggregation was characterized by an affinity value of 1.5 X 10(-1) ergs/cm2 in 10% dextran by weight in grams. In 10% by weight in grams solutions of dextran, the free energy potential for vesicle aggregation decreased as the surface charge (PS) was increased; the affinity extrapolated to zero at a PC/PS ratio of 2:1. When adherent vesicle pairs were transferred into a dextran-free buffer, the vesicles did not spontaneously separate. They maintained adhesive contact until forceably separated, after which they would not read here. Thus, it appears that dextran forms a "cross-bridge" between the vesicle surfaces.

Animals↗
PubMed1984

Adhesivity and rigidity of erythrocyte membrane in relation to wheat germ agglutinin binding.

Binding of the plant lectin wheat germ agglutinin (WGA) to erythrocyte membranes causes membrane rigidification. One of our objectives has been to directly measure the effects of WGA binding on membrane rigidity and to relate rigidification to the kinetics and levels of WGA binding. Our other objective has been to measure the strength of adhesion and mechanics of cell separation for erythrocytes bound together by WGA. The erythrocyte membrane rigidity was measured on single cells by micropipette aspiration. The slope of the suction pressure-length data for entry into the pipette provided the measure of the membrane extensional modulus. Data were collected for cells equilibrated with WGA solutions in the range of concentrations of 0.01-10 micrograms/ml. Erythrocyte-erythrocyte adherence properties were studied by micropipette separation of two-cell aggregates. First, a "test" cell was selected from a WGA solution by aspiration into a small micropipette, then transferred to a separate chamber that contained erythrocytes in WGA-free buffer. Here, a second cell was aspirated with another pipette and maneuvered into close proximity of the test cell surface, and adhesive contact was produced. The flaccid cell was separated from the test cell surface in steps at which the force of attachment was derived from the pipette suction pressure and cell geometry. In addition, we measured the time-dependent binding and release of fluorescently labeled WGA to single erythrocytes with a laser microfluorometry system. The results showed that the stiffening of the erythrocyte membrane and binding of fluorescently labeled WGA to the membrane surface followed the same concentration and time dependencies. The threshold concentration for membrane stiffening was at approximately 0.1 microgram/ml where the time course to reach equilibrium was close to 1 h. The maximal stiffening (almost 30-fold over the normal membrane elastic modulus) occurred in concentrations greater than 2 micrograms/ml where the time to reach equilibrium took less than 1 min. The WGA binding also altered the normal elastic membrane behavior into an inelastic, plastic-like response which indicated that mechanical extension of the membrane caused an increase in cross-linking within the surface plane. Similar to the stiffening effect, we observed that the membrane adhesivity of cells equilibrated with WGA solutions greatly increased with concentration greater than 0.1 microgram/ml.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Adhesion↗
PubMed1984

Static and dynamic rigidities of normal and sickle erythrocytes. Major influence of cell hemoglobin concentration.

Static and dynamic deformabilities of erythrocytes are important determinants of microcirculatory blood flow. To determine the influence of increased cellular hemoglobin concentration on these properties, we quantitated static and dynamic deformabilities of isolated subpopulations of oxygenated normal and sickle erythrocytes with defined cell densities using micromechanical manipulations of individual cells. The rheological properties measured to characterize static deformability were membrane extensional rigidity and bending rigidity. To characterize dynamic deformability of the cells, we measured the time constants for rapid elastic recovery from extensional and bending deformations. The extensional rigidity of sickle cells increased with increasing cell hemoglobin concentration while that of normal cells was independent of the state of cell hydration. Moreover, sickle cells were found to exhibit inelastic behavior at much lower cell hemoglobin concentrations than normal cells. In contrast, the dynamic rigidity of both normal and sickle cells was increased to the same extent at elevated hemoglobin concentrations. Moreover, this increase in dynamic rigidity with increasing cellular dehydration was much more pronounced than that seen for static rigidity. Both the increased static and dynamic rigidities of the dehydrated sickle cells could be greatly improved by hydrating the cells. This suggests that increased bulk hemoglobin concentration, which is perhaps inordinately increased adjacent to the membrane, plays a major role in regulating the rigidity of sickle cells. In addition, irreversible membrane changes also appear to accompany cell dehydration in vivo, resulting in increased membrane shear rigidity and plastic flow. We expect that the marked increases in rigidity of dehydrated sickle cells observed here may have a major influence on the dynamics of their circulation in the microvasculature.

Anemia, Sickle Cell↗
PubMed1984

Passive material behavior of granulocytes based on large deformation and recovery after deformation tests.

In order to better understand the in vivo rheologic behavior of white cells, we have studied the time-dependent deformability, recovery, and mechanical activation of blood granulocytes. We have used micropipette aspiration methods to measure the large deformation response and recovery after deformation characteristics of neutrophils as functions of time, temperature, and collecting media. The cell response in the pipette experiment was characterized by three time domains: the first phase was the passive deformation response to the fixed suction pressure; the second phase was an obvious transition from the passive to active motile cellular state where the cell exhibited erratic length changes in the pipette; and the third phase was the steady recovery after the suction pressure had been zeroed. Tests on white cells were carried out with three different anticoagulants to evaluate the effect of calcium on deformation and recovery behavior; also, cells were separated by centrifugation in high molecular weight dextran to determine whether or not collection and separation procedures affected the cell properties. Our results have shown that the passive deformation of granulocytes into the pipette was a continuous flow process with no approach to a static deformation limit. In addition, there was an obvious threshold pressure below which the cell would not deform and enter the micropipette. For suction pressures significantly above the threshold, granulocytes were continuously deformed with a similar functional dependence on time. The coefficient of proportionality between aspiration length and time, as well as the exponent, depended on suction pressure, pipette dimension, and temperature. It was observed that the granulocytes always recovered to the spherical state after deformation, independent of the extent of deformation or location where the cell was aspirated. Based on the recovery behavior, plus the dependence of the pressure threshold on pipette size, we propose the concept that the granulocyte membrane and cortical shell behave like a "contractile surface carpet" under tension, where the cell interior responds passively like a highly viscous liquid. The membrane cortex appears to be subject to a persistent stress (tension) of about 10(-2) dyne/cm. Our observations of passive to active transition in the pipette suction experiment indicated that granulocytes may be stimulated by deformation at room temperature. This study represents the first detailed investigation of the large deformation behavior of granulocytes, and the results indicate a simple structural model to represent the passive rheologic behavior of the granulocyte.

Elasticity↗
PubMed1984

Adherence of sickle erythrocytes to vascular endothelial cells: requirement for both cell membrane changes and plasma factors.

Hebbel and colleagues have proposed that increased adherence of sickle red cells to vascular endothelium may initiate vasoocclusive events in sickle cell disease. We have developed a micropipette technique to obtain direct, quantitative measure of the adherence of individual red cells to vascular endothelial cells. Using this technique, we found that the vast majority of sickle cells suspended in autologous plasma were strongly adherent to endothelial cells, whereas only a small fraction of normal cells were weakly adherent. Influence of plasma factors on adherence was determined by measuring adherence of sickle cells suspended in normal plasma and normal cells suspended in sickle plasma. Although over 90% of sickle cells adhered to endothelial cells in autologous plasma, the percentage of adherent cells decreased dramatically to less than 20% when the same sickle cells were suspended in normal plasma. In contrast, adhesion of normal red cells suspended in sickle plasma was only modestly increased compared to adhesion in autologous normal plasma. Our results provide direct evidence for markedly enhanced adherence of sickle cells to endothelial cells. In addition, they suggest that both cell membrane changes and plasma factors contribute to this interaction. The requirement for sickle plasma further implies that temporal changes in plasma factors may play an important role in determining the onset of vasoocclusive crisis.

Anemia, Sickle Cell↗
PubMed1983

Free energy potential for aggregation of erythrocytes and phosphatidylcholine/phosphatidylserine vesicles in Dextran (36,500 MW) solutions and in plasma.

The free energy potential (affinity) for aggregation of human red blood cells and lipid vesicles in Dextran solutions and blood plasma has been quantitated by measuring to what extent a vesicle is encapsulated by the red cell surface. The free energy reduction per unit area of contact formation (affinity) was computed from the observation of the fractional extent of encapsulation at equilibrium with the use of a relation based on the elastic compliance of the red cell membrane as it is deformed to adhere to the vesicle surface. Micromanipulation methods were used to select and transfer single lipid vesicles (2-3 X 10(-4) cm diameter) from a chamber that contained the vesicle suspension to a separate chamber on the microscope stage that contained red cells in an EDTA buffer with Dextran or whole plasma. The vesicle and a red cell were maneuvered into close proximity and contact allowed to take place without forcing the cells together. To evaluate the effects of surface charge density and steric interactions on aggregation, vesicles were made from mixtures of egg phosphatidylcholine (PC) and bovine phosphatidylserine (PS) over a range of mole ratios (PC/PS)from (1:0) to (1:1); the vesicles were formed by rehydration in buffer. The Dextran solutions were made with a sharp-cut fraction of 36,500 MW in a concentration range of 0-10% by weight in grams (wt/wt). It was found that the Dextran 36,500 MW fraction produced aggregation behavior for red cells and vesicles similar to red cell-red cell aggregation in Dextran 70,000-150,000 MW fractions, when the vesicle surface charge density was comparable with that of normal red cells (i.e., PC/PS ratio of -3:1). This result indicated that Dextran molecules penetrate between the carbohydrate groups on the red cell surface and that either steric interactions between cell surface carbohydrates are important or many of the charge groups on red cells are superficial. Electrostatic repulsion effects were apparent, as no aggregation in Dextran 36,500 MW occurred for PC/PS ratios <2.6:1; the level of affinity increased with the PC content at a specific Dextran concentration. Affinities were measured in the range of 0-2 x 10-2 ergs/cm2. When adherent red cell-vesicle pairs were transferred into a Dextran-free buffer, the pair did not spontaneously separate.They maintained adhesive contact until forcibly parted, after which they would not read here. This demonstrates that Dextran forms a "cross-bridge" between the membrane surfaces. Red cell-vesicle aggregation was also tested in whole plasma, which normally yields affinity values in the range of 2-4 x 10-3 ergs/cm2 for red cell-red cell aggregation.However, no red cell-vesicle aggregation occurred in plasma, even for pure PC vesicles. This result indicates that either the aggregating plasma proteins (primarily fibrinogen) do not bind sufficiently to the lecithin surface, or they are shielded from binding to the surface by the presence of other nonaggregating components (perhaps albumin).

Dextrans↗
PubMed1983

Thermogenic drugs for the treatment of obesity: screening using obese rats and mice.

The thermogenic activity of ephedrine, ethinyloestradiol and triiodothyronine were compared by incorporating the drugs into the diets fed to groups of adult rats and mice. The animals used were normal lean mice, hypothalamic obese mice, dietary-induced obese mice and rats, and genetically obese mice and rats. Food intake and body weight were monitored throughout and oxygen consumption measurements were made. Finally, the animals were killed and their carcasses analysed. Generally, ethinyloestradiol reduced body weight by causing anorexia. Triiodothyronine increased oxygen consumption but also increased food intake such that in most cases body weight did not change; it killed the genetically obese animals, but reduced fat in the hypothalamic and dietary induced obese animals. The animals treated with ephedrine lost body weight and body fat without increasing food intake, and had elevated oxygen consumptions. This experiment not only demonstrated marked differences between the various laboratory animal models of obesity, but also that ephedrine is a potential slimming agent. It is relatively safe and has been used by us to obtain successful breeding using the genetically obese male animals which are normally sterile.

Animals↗
PubMed1983

Cellular and molecular mechanism of action of antiestrogens.

The mechanism of action of tamoxifen and of 4-hydroxytamoxifen is reviewed at the cellular and molecular level, through the current view of the authors. Synthetic antiestrogens are mainly acting directly on breast cancer cells by interacting with the estrogen receptor (RE). They prevent estrogen action by competing with estrogens on the cytosol RE. The resulting complex is partially activated, leading to its nuclear localisation and a partial and dissociated stimulation of the expression of estrogen responsive genes. A defective and partial activation of RE induced by antiestrogen is shown in vitro by several alterations of the RE concerning the dissociation rate of ligands and the affinity for double-stranded DNA and for a monoclonal antibody against the RE. The explanation of the inhibition of tumor growth is more controversial, since the proliferation of estrogen responsive cells is not only regulated by estrogens but also by other hormones and factors. We present evidence of a direct effect of antiestrogen mediated by the RE, and discuss the mechanism of resistance to antiestrogen in RE positive breast cancer cells.

Animals↗
PubMed1982

Quantitation of surface affinities of red blood cells in dextran solutions and plasma.

Mutual affinities of red blood cell surfaces in dextran solutions and plasma have been determined experimentally. The approach was to use dual micropipet techniques to manipulate cells and spherical cell "fragments" into position for contact. After contact, the red cells encapsulated the fragments to an extent that depended on the affinity. Surface affinity is defined as the reduction in free energy per unit area of interface that is associated with formation of adhesive contact. The surface affinity was calculated with the use of a minimum free energy analysis and knowledge of the red cell membrane elastic properties. With this approach, surface affinities were measured for normal and neuraminidase-treated red cells in plasma and various solutions of dextran. The data presented are the first direct measurements of the affinity of a biological membrane for another surface in a well-defined system. The peak surface affinities of normal red blood cells were found to be 4.9 x 10(-3) erg/cm2 in D70, 2.2 x 10(-2) erg/cm2 in D-150, and 2.0 x 10(-3) erg/cm2 in plasma. Neuraminidase-treated cells had higher affinities than normal cells: at least 2.8 x 10(-2) erg/cm2 in D70 and 1.8 x 10(-3) erg/cm2 in D28, which does not aggregate normal red cells.

Dextrans↗
PubMed1982

Two-compartment comparison of gentamicin and tobramycin in normal volunteers.

The objective of this study was to determine whether differences in tissue accumulation observed upon multiple dosing of aminoglycosides in hospitalized patients could be identified in appropriate single-dose studies in normal volunteers. Ten volunteers received single intravenous doses of 1.0 mg of gentamicin and tobramycin per kg of body weight in randomized crossover fashion. Multiple serum and urine samples were collected during the next 30 days. Serum aminoglycoside concentrations and urinary excretion rates were fitted to a two-compartment pharmacokinetic model, and parameters were derived. Tobramycin exhibited a higher clearance (P less than 0.08) and a lower volume of distribution at steady state (P less than 0.1), neither of which was significant. Tobramycin also showed a significantly lower predicted amount of drug in the body at steady state (P less than 0.05). These differences are consistent with observations made in patients receiving multiple doses. Single-dose studies appear to be capable of discriminating pharmacokinetic characteristics relevant to the comparative nephrotoxic potential of these two aminoglycosides.

Aged↗