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Biomedical subjects

R Meyer

Publications and source records attributed to R Meyer.

At least 217 records · Page 12Linked to original sources
PubMed1991

Stereochemistry and size of sugar head groups determine structure and phase behavior of glycolipid membranes: densitometric, calorimetric, and X-ray studies.

The role carbohydrate moieties play in determining the structure and energetics of glycolipid model membranes has been investigated by small- and wide-angle X-ray scattering, differential scanning densitometry (DSD), and differential scanning microcalorimetry (DSC). The dependence of a variety of thermodynamic and structural parameters on the stereochemistry of the OH groups in the pyranose ring and on the size of the sugar head group has been studied by using an homologous series of synthetic stereochemically uniform glyceroglycolipids having glucose, galactose, mannose, maltose, or trimaltose head groups and saturated ether-linked alkyl chains with 10, 12, 14, 16, or 18 carbon atoms per chain. The combined structural and thermodynamic data indicate that stereochemical changes of a single OH group in the pyranose ring can cause dramatic alterations in the stability and in the nature of the phase transitions of the membranes. The second equally important determinant of lipid interactions in the membrane is the size of the head group. A comparison of lipids with glucose, maltose, or trimaltose head groups and identical hydrophobic moieties has shown that increasing the size of the neutral carbohydrate head group strongly favors the bilayer-forming tendency of the glycolipids. These experimental results provide a verification of the geometric model advanced by Israelachvili et al. (1980) [Israelachvili, J. N., Marcelja, S., & Horn, R. G. (1980) Q. Rev. Biophys. 13, 121-200] to explain the preferences lipids exhibit for certain structures. Generally galactose head groups confer highest stability on the multilamellar model membranes as judged on the basis of the chain-melting transition. This is an interesting aspect in view of the fact that galactose moieties are frequently observed in membranes of thermophilic organisms. Glucose head groups provide lower stability but increase the number of stable intermediate structures that the corresponding lipids can adopt. Galactolipids do not even assume a stable intermediate L alpha phase for lipids with short chain length but perform only Lc----HII transitions in the first heating. The C2 isomer, mannose, modifies the phase preference in such a manner that only L beta----HII changes can occur. Maltose and trimaltose head groups prevent the adoption of the HII phase and permit only L beta----L alpha phase changes. The DSD studies resulted in a quantitative estimate for the volume change associated with the L alpha----HII transition of 14-Glc. The value of delta v = 0.005 mL/g supports the view that the volume difference between L alpha and HII is minute.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry, Differential Scanning↗
PubMed1991

Cloning of the DNA-binding subunit of human nuclear factor kappa B: the level of its mRNA is strongly regulated by phorbol ester or tumor necrosis factor alpha.

The DNA binding subunit of nuclear factor kappa B (NF-kappa B), a B-cell protein that interacts with the immunoglobulin kappa light-chain gene enhancer, has been purified from nuclei of human HL-60 cells stimulated with tumor necrosis factor alpha (TNF alpha), and internal peptide sequences were obtained. Overlapping cDNA clones were isolated and sequenced. The encoded open reading frame of about 105 kDa contained at its N-terminal half all six tryptic peptide sequences, suggesting that the 51-kDa NF-kappa B protein is processed from a 105-kDa precursor. An in vitro synthesized protein containing most of the N-terminal half of the open reading frame bound specifically to an NF-kappa B binding site. This region also showed high homology to a domain shared by the Drosophila dorsal gene and the avian and mammalian rel (proto)oncogene products. The level of the 3.8-kilobase mRNA was strongly increased after stimulation with TNF alpha or phorbol ester. Thus, both factors not only activate NF-kappa B protein, as described previously, but also induce expression of the gene encoding the DNA-binding subunit of NF-kappa B.

Amino Acid Sequence↗
PubMed1991

Potential antitumor phenoxazines.

From the various studies cited, spanning more than forty years, it is clear that some members of the phenoxazine and benzophenoxazine dye family selectively stain certain tumors and, when given in suitable concentrations in the feed, can prolong life and shrink tumors. In addition, some use has been made of these compounds as carriers for other antitumor agents based upon the idea of selective accumulation into tumor tissue. Although many analogs have been made and examined, the work has been done in a relatively unfocused manner and the field could benefit from a systematic study of the effect of structure on biological activity. None of the synthetic materials prepared and tested to date has the potency of the outstanding antitumor natural products bearing the ring system of the actinomycins. Advances in our understanding of the molecular mode of action of the actinomycins, based in large measure upon x-ray studies, suggest some avenues for future exploitation. To date, attempts to prepare simplified actinomycins or elaborate phenoxazines to accomplish this have been disappointing.

Animals↗
PubMed1991

Detection of Escherichia coli and identification of enterotoxigenic strains by primer-directed enzymatic amplification of specific DNA sequences.

The polymerase chain reaction (PCR) was used to amplify DNA sequences from the malB operon of Escherichia coli. All E. coli strains tested yielded the specific DNA fragment. No amplification products were obtained with other Enterobacteriaceae. E. coli strains which produce enterotoxins were identified with additional primer pairs specific for the genes coding for the heat-labile toxin type I (LTI) and the heat-stable toxin type I (STI). Amplification products were identified by DNA-DNA hybridization. Alternatively, restriction endonuclease analysis was used for identification and to distinguish between different alleles of the enterotoxin genes. The detection limit was 10 bacteria. The PCR systems were validated by testing 27 E. coli of known enterotoxigenic properties. The PCR results were consistent with factual toxin production as determined by immunoassays. In addition, 58 E. coli strains isolated from soft cheese and mayonnaise were analyzed by PCR. One strain from a cheese sample was found to have the genetic information for STI production. This strain produced STI as determined by enzyme-linked immunosorbent assay.

Animals↗
PubMed1991

Rotational step-cut osteotomy for treatment of metacarpal and phalangeal malunion.

Metacarpal and phalangeal malunion after fracture or replantation frequently causes rotational deformities with scissoring during digital flexion. Transverse osteotomy at the metacarpal base has been advocated for derotation, but this only partially corrects scissoring resulting from phalangeal malunion. We describe the results of rotational step-cut osteotomies at the site of malunion. There were twenty-three osteotomies in eighteen patients; seven metacarpal and sixteen in the proximal phalanx. The value of the technique is supported by the results; speedy healing of bone, satisfactory alleviation of deformity, and a useful gain in range of motion in many patients.

Adult↗
PubMed1991

Morphometric, histochemical and autoradiographic studies on myocardial cells in experimental cardiac hypertrophy and ischemia.

Experimental studies were conducted into 170 adult male Wistar rats for the purpose of analysis of cellular adaptation processes of the myocardium to acute ischemia. One group of the animals were exposed to physical endurance training, i.e. 180 h of swimming exercises, up to 3 h daily. Positive verification of cardiac hypertrophy was considered a measure of accomplished cellular adaptation. Training-induced increase of relative and absolute heart weight was 25 and 30%, respectively. Acute myocardial ischemia had been produced by ligature of the left coronary artery. There were no significant differences between trained and untrained animals for incidence and size of infarction and postoperative lethality, while cardiac decompensation was less often recorded from trained animals. To study cellular adaptation as well as differences between trained and untrained animals, tissue samples were taken from the non-ischemic part of the left ventricle and checked by means of histology, electron microscopy, morphometry, quantitative histochemistry, and histo-autoradiography 1, 2, 4, 7, and 14 days after occlusion of the coronary artery. The studies have shown endurance training to result in unambiguous modification of structural as well as functional response of the nonischemic heart. Included in such structural modification at cellular level are significant changes in mitochondrial membranes, sarcoplasmic reticulum, and T-system. Structural modification was reflected in changes to the oxidative enzymes and DNA metabolism. Different patterns of cellular reaction could be positively verified up to 14 days after myocardial infarction.

Animals↗
PubMed1991

Distribution of cartilage proteoglycan (aggrecan) core protein and link protein gene expression during human skeletal development.

The distribution of cartilage proteoglycan core protein (aggrecan) and cartilage proteoglycan link protein was investigated by in situ hybridization during different stages of human skeletal development. Aggrecan and link protein expression were confined to chondrocytes of the developing skeleton and other cartilaginous structures. Distribution and intensity of the signal was identical with aggrecan as compared to link protein probes. Parallel to the calcification of cartilaginous matrix, chondrocytes of this area lost the expression of aggrecan and link protein specific mRNA and stayed negative throughout the following stages of skeletal development. Highest expression was found in the lower proliferative and upper hypertrophic zone whereas the resting zone showed less expression. Aggrecan gene expression was additionally investigated in iliac crest biopsies of 3 patients with pseudoachondroplasia and compared to age-matched controls. Distribution and intensity of staining revealed no abnormalities. Thus, the phenotypic changes during chondrocyte maturation are accompanied by distinct changes in aggrecan and link protein gene expression. This pattern was maintained in the growth plate of patients with pseudoachondroplasia.

Aggrecans↗
PubMed1991

Evidence for atrial natriuretic peptide (ANP) synthesis and the presence of ANP-transducing receptors in the rat olfactory bulb.

This study demonstrates the presence of both atrial natriuretic peptide (ANP) precursor and ANP transcripts in the rat olfactory bulb (OB), a key brain structure involved in the generation of olfaction-dependent behavior. In addition to synthesizing ANP, the OB contains ANP-transducing receptors coupled to the guanylate cyclase system but it is devoid of ANP "clearance receptors." The characterization of biologically active ANP receptors and the evidence for in situ ANP synthesis in this region of the CNS adds credence to the hypothesis that the peptide plays a putative role in olfaction.

Animals↗
PubMed1991

Morphological, biochemical, and electrophysiological characterization of a clonal cell (H9c2) line from rat heart.

Morphological, electrophysiological, and biochemical properties of H9c2 cells, a permanent cell line derived from rat cardiac tissue, were studied. Although the lectin binding pattern revealed similar sugar residues in the surface coat of H9c2 cells and isolated rat cardiocytes, heart-specific morphological structures could not be detected in H9c2 cells. Under physiological ionic conditions, H9c2 cells exhibited an outwardly rectifying, transient K+ current. When this current component was blocked by Ba2+ and Cs+, we observed an inward current through Ca2+ channels (15.8 +/- 2.2 pA/pF, n = 18, measured as Ba2+ current) that showed all characteristics of cardiac L-type currents. The activation kinetics were fast, and the current was stimulated by isoproterenol. The effect of isoproterenol was mimicked by forskolin or intracellularly applied cAMP. In radioligand binding experiments, we identified a specific, saturable, stereoselective and reversible high-affinity [3H]-(+)PN 200-110 binding with a dissociation constant Kd = 0.53 +/- 0.28 nM and a maximal specific binding of Bmax = 129.3 +/- 16.1 fmol/mg protein. There was an additional low-affinity/high-capacity binding site, which is unlikely to be related to a Ca2+ channel protein. Signal-transducing G proteins in membranes were characterized by [32P]ADP-ribosylation catalyzed by bacterial toxins and by the use of various antibodies. Cholera toxin substrates of 42 and 45 kd were identified that apparently correlated to Gs alpha-subunits. Pertussis toxin substrates of 40-41 kd were tentatively identified as Gi alpha-subunits. The G protein Go was absent or at least extremely low in concentration.

Adrenergic beta-Agonists↗
PubMed1991

Viral haemorrhagic disease of rabbits in Mexico: epidemiology and viral characterization.

A fatal disease of rabbits was first reported in the People's Republic of China in 1984. Since 1986, the disease has been reported in most countries of Europe and in the Republic of Korea. In 1989 a similar disease, presumably linked to the importation of rabbit meat from the People's Republic of China, spread rapidly through ten states in Mexico; it was eradicated during the same year by "stamping-out" measures. In Mexico, as was the case in other outbreaks, morbidity and mortality reached 80-90% with few clinical signs. In pathogenesis studies, the primary sites of replication were in the small intestinal crypt and villous epithelium, hepatocytes and splenic lymphocytes. Many organs, including the lung and kidney, contained acutely infarcted tissue and haemorrhages resulting from a terminal disseminated intravascular coagulopathy. The disease and the characteristics of the virus isolated in Mexico are similar to isolates from Europe and the Republic of Korea. The comparative morphologic, from Europe and the Republic of Korea. The comparative morphologic, immunologic, and in situ nucleic acid hybridization evidence for a parvovirus aetiology are summarized.

Animals↗
PubMed1991

[Concept and technique for closure of septum defects].

A surgical concept for the closure of perforations of the septum is presented. Small and medium-sized defects are closed by a one-step extramucosal technique also used in rhinoplasties. Tissue tubes of mucoperichondrium, mucoperiosteum and the upper lateral cartilage are mobilized in both nasal lumina. Parts of the lamina quadrangularis are dissected and shifted to close the defect. Very large defects with a diameter of more than 3 cm are closed in a three-step technique. A spoon-shaped flap from the oral vestibule with a piece of ear cartilage attached is inserted into the perforation. The cartilage is covered with oral mucosa on both sides. These procedures are superior to traditional techniques in terms of both blood supply and safe closure.

Humans↗
PubMed1991

[Quantitative and qualitative findings in endomyocardial biopsies from patients with and without hypertension].

Histological and morphometric investigations were made of left-ventricular endomyocardial bioptates which had been obtained from 19 male patients with so-called latent cardiomyopathy as well as from 21 patients with positively verified hypertension and with angiographically excluded coronary artery sclerosis. The patients were additionally divided in two cohorts according to the weight of the left ventricle below and above 170 g. Inflammatory and ischaemic conditions were, above all, histologically recorded from the first group, while microangiopathy was more frequent in the second. Aspects relating to differential diagnosis and possible relationship between microangiopathy and hypertension were discussed in some detail. Endomyocardial biopsy appears to be justified for patients with hypertension (and also for those with so-called latent cardiomyopathy), if other heart diseases are to be ruled out. Subjective perception of hypertension of myocardial cells was compared to measured myocardial cell diameters. Hypertension of myocardial cells was subjectively overestimated in roughly 50% of all cases. Such subjective overestimation did not necessarily lead to histological diagnosis of hypertension. The conclusion was suggested that subjective assessment of hypertension was sufficient for routine checks. No relationship was found to exist between the weight of the left ventricle or presence of hypertension, on the one hand, and diameter of myocardial cells or volume fraction of the interstitium, on the other.

Cardiomyopathies↗
PubMed1991

[The principles of two-teeth-mechanics in straight-wire-technique].

Application of straight-wire-technique leads to expression of complicated biomechanical systems. If these--according to Burstone--are subdivided into simple couples of teeth, it is possible to determine the moments and forces acting on one side of a tooth. However the significant factor for clinical tooth movement are the resulting forces and moments. These can be computed by adding the vectors of the forces and moments acting on both sides of a tooth. Consequently the movement of a single tooth results from the geometry of three teeth. This can be simulated by the superimposition of two systems of two teeth.

Dental Stress Analysis↗