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At least 235 records · Page 13Linked to original sources
PubMed2000

[Transmural heterogeneity of the left ventricular wall: subendocardial layer and subepicardial layer].

The myocardium of the left ventricular wall is not homogeneous, but demonstrates transmural heterogeneity in myocardial blood flow, myocardial metabolism, and contraction and relaxation dynamics. Reimer and colleagues recognized that irreversible injury of the ischemic myocardium develops as a transmural wavefront, occurring first in the subendocardial myocardium, and with longer periods of ischemia, the wavefront of necrosis moves from the subendocardial zone across the wall to progressively involve more of the transmural thickness of the ventricular wall, ultimately becoming nearly transmural. This phenomenon was named the "wavefront phenomenon", and is the morphological counterpart of the transmural heterogeneity of the metabolism and blood flow. Autoregulation of myocardial blood flow is accomplished by changes in intramyocardial vascular resistance and intramyocardial pressure. It is more difficult to maintain the autoregulation in the subendocardial myocardium because contraction is greater, oxygen demand is greater, and myocardial pressure is higher in the subendocardium than in the subepicardial layer. In the normal myocardium, contraction is greater in the subendocardial layer, as is wall stress, accounting for the higher subendocardial energy requirements. Consistent with these findings, higher rates of metabolic activity and greater oxygen extraction are found in this region. As a consequence, ischemia becomes more severe and myocardial cells undergo necrosis first in the subendocardium. Under normal conditions, production and utilization of high-energy phosphates [adenosine triphosphate(ATP) and creatine phosphate] in the subendocardial myocardium are more active than in the subepicardial myocardium, but decline more easily in the subendocardium during ischemia, which induces the subendocardial ischemic injury. Lower production of Ca(2+)-ATPase in the subendocardium might also contribute to the subendocardial injury. Wavefront necrosis starts from the subendocardium, but the production of high-energy phosphates in the subepicardium is known to increase and compensate for the reduction in high-energy phosphate production in the subendocardium. Animal experiments have shown that systolic thickening of the endocardial half of the ventricular wall is double that in the epicardial half. Today, this can be confirmed in humans with the tissue Doppler tracking method which is completely noninvasive. Furthermore, the subepicardial half of the ventricular wall is known to compensate for the decreased systolic thickening of the subendocardial half in the case of subendocardial injury, which is called vertical compensation and is the mechanical counterpart of the concept of metabolic compensation. Many new technologies, including the tissue Doppler tracking method, magnetic resonance imaging tagging, and myocardial contrast echocardiography, will give more accurate information about the myocardial heterogeneity of layer-by-layer motion and blood flow, and will contribute to early detection and quantitative estimation of ischemia and other diseases of which the main lesion is in the subendocardium.

Animals↗
PubMed1992

[Three methods of placing a single-row layer-by-layer everted intestinal suture].

The three methods for placing a single-row layer-by-layer everted intestinal suture with the suture ligature knots situated in a different manner relative to anastomotic surfaces are presented. Using the methods suggested, 53 patients were operated on, who underwent formation of 87 anastomoses. The results of studies indicate that the use of a single-row layer-by-layer everted suture permits to reduce considerably the incidence of postoperative complications, promotes early restoration of a function of the organ operated on.

Anastomosis, Surgical↗
PubMed1986

The tetragonal surface layer of Clostridium aceticum: three-dimensional structure and comparison with the hexagonal layer of Clostridium thermohydrosulfuricum.

The regular surface layer (S-layer) of Clostridium aceticum has been isolated and the three-dimensional structure determined to a resolution of 2.0 nm from tilt series of negatively stained preparations. It has tetragonal symmetry with a lattice constant of 12 nm and a thickness of 6 nm; there are probably 4 protein monomers per unit cell. A large proportion of the protein is concentrated in massive "cores" at the major four-fold axes which are situated towards the inner surface of the layer. From these cores, delicate arms extend towards the minor four-fold axes, where secondary connectivity is established near the exterior surface. When viewed from the outside, each of the cores appears to have a large central depression, rather than a true "pore". Since this general pattern of mass distribution is shared by the hexagonal S-layer of Clostridium thermohydrosulfuricum, some consideration has been given to the possible evolutionary steps leading to changes in symmetry. From modelling experiments, it is evident that the change from four-fold to six-fold symmetry in this instance could be accomplished simply by the loss of a structural "domain" from the protomer.

Bacterial Proteins↗
PubMedDate not supplied

[Stability of vitamins in parenteral nutrition: a comparison of multi-layer and uni-layer bags].

The goal of this study was to compare vitamin A, E, C, B12, B2 and folic acid concentrations in parenteral nutrition solutions in multilayer and single layer EVA bags. Two different bag trade marks were used: Bexen and Miramed. We measured vitamin concentrations at 24 hours, the fifth and seventh day after refrigerated storage and the eighth day after 24 hours at room temperature. Trace-element and temperature influence were studied. Vitamins A, E, B12, B2 and folic acid had a similar behaviour with multi-layer and one-layer bags. No differences were observed between solutions with and without trace-elements. The concentrations remained within acceptable ranges. We observed a clear decrease of vitamin C, that can be avoided with the use of multilayer bags. These bags can be useful in home parenteral nutrition or when vitamins cannot be added immediately before its administration. An important loss of vitamin A was also detected in parenteral nutrition solutions without lipids, both in multilayer and single layer bags, despite photoprotection and refrigeration.

Ascorbic Acid↗
PubMed2006

Conditioning effect on dentin, resin tags and hybrid layer of different acidity self-etch adhesives applied to thick and thin smear layer.

OBJECTIVES: to assess the conditioning effect (CE) of self-etch adhesives of different acidity applied to thick and thin smear layer (SL), the corresponding resin tags (RT) and hybrid layer (HL). METHODS: Twenty-seven molars had their occlusal dentin exposed and were sectioned into two halves. Each of them was ground with a 60 or 600-grit SiC paper, respectively for thick and thin SL production. Three self-etch adhesives: a mild (Clearfil SE Bond), an intermediary (Optibond Solo SE and Solo Plus) and a strong (Tyrian Self Priming Etchant+One Step Plus) and an etch-&-rinse system (Scotchbond Multi Purpose Plus) were used. For CE evaluation, the self-etch primers were applied and rinsed off with acetone and alcohol prior to SEM preparation. For RT and HL specimens self-etch adhesives were applied and restored with Z-250. For RT specimens, dentin was removed with HCl (6N) and NaClO (1%) baths. The HL specimens were fixed, dehydrated, dried with HMDS, embedded, polished and slightly demineralized (6N HCl) and deproteinized (1% NaClO). After gold sputtering they were observed by SEM. RESULTS: The thick smear layer was clearly not totally removed by the mild self-etch primer. RT varied in density and shape among the self-etch adhesives. Thicker HL was observed for the strong self-etch and etch-&-rinse adhesives. CONCLUSIONS: The etch-&-rinse adhesive presented the thickest HL and was the only adhesive to produce RT in high density and uniform distribution along the whole dentin surface, independently of the SL thickness.

Acid Etching, Dental↗
PubMed1988

Separation of lipids by new thin-layer chromatography and overpressured thin-layer chromatography methods.

New methods were developed for the separation of major lipid classes varying in polarity from cholesterol esters to lysophosphatidylcholine. The methods were used for the analysis of extracts obtained from human sera. The lipids were separated by overpressured thin-layer chromatography, classical thin-layer chromatography, and one-dimensional thin layer chromatography, using six different solvent systems for development. These techniques are also suitable to separate unsaturated and saturated cholesterol esters according to the number of carbon atoms and double bond numbers of their constituent fatty acids.

Cholesterol Esters↗
PubMed1975

Thin-layer chromatography of sulphonamides on silica gel G and polyamide layers by means of a polar mobile phase.

A thin-layer chromatographic system based on polyamide or silica gel G layers and an aqueous mobile phase was used for the separation of a series of sulphonamides. A linear relationship between RM values on polyamide layers and the acetone concentration in the mobile phase allowed the calculation of extrapolated RM values. The influence of the nature of the stationary phase on the migration of compounds is discussed.

Acetone↗
PubMed1978

Quantitative high-performance thin-layer chromatography of lipids in plasma and liver homogenates after direct application of 0.5-microliter samples to the silica-gel layer.

Lipid profiles were determined by high-performance thin-layer chromatography (HPTLC) after direct application of 0.5 microliter plasma from capillary blood to the silica-gel layer. Coefficients of variation for the fluorescence measurements were 2.1% for phosphatidylcholine. The recovery of known amounts of lipid was 96--100%. A linear relationship between peak area and amount of lipid was found in the nmole range, corresponding to the amount of lipid in 0.125--0.75 microliter Lipid-Trol, which served as the standard reference sample. The plasma lipids of healthy subjects and of patients suffering from various illnesses were analyzed using reference methods and HPTLC. Identical values were obtained for cholesterol esters, triacylglycerols and phosphatidylcholine. Free cholesterol values determined by HPTLC were slightly lower (7%). The correlation between data obtained by reference methods and HPTLC was as follows: cholesterol, r = 0.938; cholesterol esters, r = 0.964; triacylglycerols, r = 0.985; phosphatidylcholine, r = 0.938. The separaiton and quantitation of liver lipids using HPTLC after direct application of the tissue homogenate to the silical-gel layer was carried out. Comparison with reference methods revealed that HPTLC gave higher cholesterol values (24%). The triacylglycerol concentrations, however, were identical under both methods and correalted satisfactorily (r = 0.959).

Adult↗
PubMed1991

[Retinol Acetate Reference Standard for Thin-layer Chromatography (Control 901) and Retinol Palmitate Reference Standard for Thin-layer Chromatography (Control 901) of National Institute of Hygienic Sciences].

The raw materials of retinol acetate and retinol palmitate were examined for the preparation of the "Retinol Acetate Reference Standard for Thin-layer Chromatography" and "Retinol Palmitate Reference Standard for Thin-layer Chromatography", respectively. Analytical data obtained were as follows: thin-layer chromatography, no impurities were detected in retinol acetate and one impurities was detected in retinol palmitate; The Rf values of retinol acetate and retinol palmitate were consistent with those of Reference Standards (Control 713), respectively; ultraviolet spectrum, lambda max = 326 approximately 327 nm; relative extinction, within the range reported in JPXI; weight variation of capsules, retinol acetate 224.0 +/- 15.5 mg (RSD 6.9%), retinol palmitate 222.0 +/- 13.8 mg (RSD 6.2%); assay, retinol acetate 57000 I.U./g, retinol palmitate 57000 I.U./g. Based on the above results, these raw materials were authorized to be the Reference Standards of the National Institute of Hygienic Sciences.

Chromatography, Thin Layer↗
PubMed1996

The superficial layer of human articular cartilage is more susceptible to interleukin-1-induced damage than the deeper layers.

OBJECTIVE: To compare the responses of chondrocytes from superficial and deep layers of normal human articular cartilage to interleukin-1 (IL-1) and IL-1 receptor antagonist protein (IRAP), and to evaluate the binding sites for IL-1 on these cells. METHODS: Cartilage and chondrocytes from superficial and deeper layers of human femoral condyles were cultured with and without IL-1 in the presence and absence of IRAP. The effect of these agents on 35S- proteoglycan synthesis and catabolism and production of stromelysin and tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by biochemical and immunologic assays. Receptor binding was evaluated using 125I-labeled IL-1. RESULTS: IL-1 induced more severe inhibition of proteoglycan synthesis and a lower ratio of secreted TIMP-l:stromelysin in chondrocytes from superficial cartilage than those from deeper cartilage. IRAP blocked responses to IL-1 more effectively in chondrocytes from deep cartilage than those from superficial cartilage. Chondrocytes from the articular surface showed approximately twice the number of high-affinity b!nding sites for IL-1 as did cells from deep cartilage. CONCLUSION: Chondrocytes from the surface of articular cartilage show a greater vulnerability to the harmful effects of IL-1 and are less responsive to the potential therapeutic effects of IRAP than cells in the deeper layers of the tissue.

Adolescent↗
PubMed2001

Encapsulation of proteins by layer-by-layer adsorption of polyelectrolytes onto protein aggregates: factors regulating the protein release.

A novel method of protein encapsulation is proposed. Preformed protein aggregates are covered with polyelectrolyte layers by means of layer-by-layer adsorption. The polyelectrolyte membrane prevents protein leakage out of the capsule. Using chymotrypsin as a model enzyme the capsule wall selective permeability was demonstrated for substrates and inhibitors of different molecular weight and solubility.

Adsorption↗
PubMed1975

A comparison of one layer and two layer techniques for colorectal anastomosis.

In a randomized prospective clinical trial and layer and two layer techniques have been compared in 92 patients undergoing colorectal anastomosis. The results were assessed radiologically by barium studies on the tenth postoperative day. There was no significant difference in the incidence of anastomotic breakdown with either technique when the anastomosis was performed above the pelvic peritoneal reflection. When the anastomosis was situated below the pelvic peritoneum the incidence of dehiscence was significantly greater when a two layer technique was used.

Barium Sulfate↗
PubMed2005

Structural diversity of alpha-amino acid based layer-block dendrons and their layer-block sequence-dependent gelation properties.

A library of G1-G3 alpha-amino acid based layer-block dendrons 1-6 containing different amino acid residues in the different concentric layers was prepared by solution-phase peptide synthesis. The structures of these dendrons were characterized by 1H and 13C NMR spectroscopy and, except for the G3 series of compounds, by mass spectrometry. The purities of these compounds were also determined by size-exclusion chromatography. Owing to the presence of a large number of amide groups, these dendrons exhibit unusually strong self-aggregating properties in both polar and nonpolar solvents. Some of these dendrons are found to be extremely good organogelators towards aromatic solvents with minimum gel concentrations approaching 4 mg mL(-1). Their gelation ability is found to be highly dependent on the nature of the amino acid compositions, the amino acid layer-block sequence within the dendritic architecture and the nature of the focal-point functionality. IR spectroscopic analysis indicates that gelation is induced by intermolecular hydrogen bonds. Circular dichroism studies suggest the formation of hierarchical chiral structures in the gel state, although the existence of chiral morphologies could not be observed by scanning electron microscopy.

Amino Acids↗
PubMed2007

Layer-by-layer assembly of biomacromolecules on poly(ethylene terephthalate) films and fiber fabrics to promote endothelial cell growth.

Poly(ethylene terephthalate) (PET) film and PET vascular graft were modified by layer-by-layer (LBL) assembly of collagen and chondroitin sulfate (CS) to mimic the natural composition and structure of extracellular matrix. PET materials were first hydrolyzed to endow the surfaces with negative charge. Alternative assembly of positively charged collagen and negatively charged CS was then conducted in an LBL manner to produce biological multilayers. X-ray photoelectron spectroscopy confirmed the occurrence of hydrolysis and existence of collagen and CS. The stepwise layer growth on the PET film was monitored by UV-vis spectroscopy. The multilayers had sufficient stability to pass through the cell culture period (8 days). In vitro endothelial cell culture revealed that the incorporated biomacromolecules could significantly improve the cell attachment, proliferation, and viability. Cells showed more spreading morphology with preserved phenotype, as illustrated by scanning electron microscopy and factor VIII-related antigen immunocytochemistry, respectively.

Blood Vessels↗
PubMed2000

The Primary Electroviscous Effect: Thin Double Layers (akappa>>1) and a Stern Layer.

The primary electroviscous effect due to the charge clouds surrounding spherical charged particles suspended in an electrolyte was studied by Hinch and Sherwood (J. Fluid Mech. 132, 337 (1983)) in the limit of double layers thin compared to the particle radius a. Here we introduce the effect of a dynamic Stern layer into that analysis, in order to explain the numerical results of Rubio-Hernández et al. (J. Colloid Interface Sci. 206, 334 (1998)) in terms of the ratio of the tangential ionic fluxes within the charge cloud to those within the Stern layer. The predictions of the asymptotic analysis are compared with those of numerical computations. The thickness of the charge cloud is characterized by the Debye length kappa(-1). If akappa>10 the predictions of the asymptotic analysis exhibit the same qualitative behavior as the numerical results, but akappa>1000 is required to achieve quantitative agreement to within 2.5%. Copyright 2000 Academic Press.

Journal Article↗
PubMed1993

Orientational influences of layer V of visual area 18 upon cells in layer V of area 17 in the cat cortex.

We examined the orientation tuning curves of 86 cells located in layer V of area 17, before, during, and after focal blockade of a small (300-microns diameter) region of near-retinotopic register in layer V of area 18 of quantitatively established orientation preference. Such focal blockade revealed three distinct populations of area 17 layer V cells-cells with decreased responses to stimuli of some orientations (21%), cells with increased responses to stimuli of some orientations (43%), and cells unaffected by the focal blockade (36%). These effects were clearcut, reproducible, and generally directly related to the known receptive field properties of the cell recorded in area 18 at the center of the zone of blockade. These effects were also analyzed in terms of alterations in orientation bandwidth in the cells in area 17 as a result of the blockade-bandwidth increases (22%) and decreases (24%) were found; however, these changes were essentially unrelated to the measured receptive field properties. Inhibitory and excitatory effects were most pronounced when the regions in areas 17 and 18 were of like ocular dominance and were of similar orientation preference. Inhibitory effects (suggesting a normally excitatory input) were most dependent upon the similarity of receptive fields; excitatory effects (suggesting a normally inhibitory input) were less heavily dependent.

Animals↗
PubMed1993

Influence of layer V of area 18 of the cat visual cortex on responses of cells in layer V of area 17 to stimuli of high velocity.

Focal blockade of restricted regions in layer V of area 18 was used to assess the contribution of this region to the responses to high-velocity stimuli of cells in retinotopically matched, layer V in area 17. In 40% of cases, blockade within area 18 revealed responses of area 17 cells to high-velocity stimuli to which they previously showed only poor responses. Stimulus specificity of the cells in area 17 was otherwise unaltered. All effects were reversible and repeatable. We suggest that a component of the output of layer V from area 18 normally suppresses the responses of retinotopically matched cells within area 17 to stimuli of high velocity, thereby enhancing the specificity of those cells to stimuli of low velocity.

Animals↗