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Biomedical subjects

R Engel

Publications and source records attributed to R Engel.

At least 55 records · Page 3Linked to original sources
PubMed1991

High-performance liquid chromatographic method for the determination of occupational exposure to the pesticide abamectin.

As part of a survey of occupational exposure to pesticides in greenhouses for growing ornamentals, analytical methods were developed and validated for the measurement of exposure of workers to the pesticide abamectin. Abamectin consists of a mixture of avermectin-B1a and avermectin-B1b, which are members of a class of fermentation products of the soil microorganism Streptomyces Avermitilis. Because of the high molecular weight of the avermectins (greater than 800 daltons), high-performance liquid chromatography (HPLC) was the analytical method of choice. Previously described HPLC methods that used fluorescence detection were adapted and validated for the determination of dermal exposure by the analysis of cotton gloves and foliar dislodgeable residue. IOM samplers (developed at the Institute of Occupational Medicine, Edinburgh, U.K.) for collecting the inspirable fraction of dust or aerosols were tested for the determination of airborne abamectin concentrations in greenhouses. An analytical procedure considerably simpler than published methods appeared suitable for the determination of abamectin residues on cotton gloves and on greenhouse foliage. Analytical recovery from cotton gloves, solutions of foliar dislodgeable residues, and air-sampling filters was essentially complete. However, air concentrations of abamectin could not be reliably measured by using the IOM sampling device because of breakdown during sampling. Between-day coefficients of variation for solutions of dislodgeable residue and cotton glove extracts were between 3% and 6% for abamectin concentrations between 5 and 140 micrograms/L.

Aerosols↗
PubMed1991

The role of lipoxygenases in endotoxin-induced cytokine production.

The LPS induced synthesis of tumor necrosis factor in macrophage cultures, as determined in a fibroblast cytolysis assay was found to be effectively blocked by inhibitors of lipoxygenases. Likewise, the presence of tumor necrosis factor in serum of D-galactosamine sensitized mice after challenge with endotoxin was suppressed by the lipoxygenase inhibitors. From LPS-treated macrophages 13-hydroxylinoleic acid, a lipoxygenase product was isolated, which is significantly increased after LPS treatment of the cells, covalently bound to cellular constituents and was found to counterbalance the suppression of TNF-synthesis by a lipoxygenase inhibitor when added to macrophages exogenously.

Animals↗
PubMed1990

Growth control in mammalian cells by cell-cell contacts.

Growth of normal diploid mammalian cells in vitro is strongly regulated by the actual cell density. Cell-cell contacts via specific plasma membrane glycoproteins whose glycan moieties interact with specific receptors has been found to be a main growth regulatory principle. Malignant growth is suggested to result from impaired function of these receptors.

Cell Adhesion↗
PubMed1989

Mononuclear phagocytes and eicosanoids: aspects of their synthesis and biological activities.

Mononuclear phagocytes convert arachidonic acid and other unsaturated fatty acids from intracellular sources to a variety of oxygenated metabolites such as prostaglandins and leukotrienes which are secreted into the surrounding medium. Other oxidative products such as hydroxylinoleic acids are reacylated into cellular constituents. The underlying metabolic pathways are activated by numerous stimuli of exogenous or endogenous origin. Depending on the state of activation and cell differentiation, the organ of origin and the nature of the stimulus used, macrophages elaborate a distinct spectrum of oxidative arachidonic acid metabolites. The contribution of these metabolites to the proinflammatory properties of macrophages is twofold: As autocrine signals they modulate the synthesis of diverse macrophage products and they influence cellular functions of other cells such as T-lymphocytes.

Animals↗
PubMed1989

Influence of CGP 361A, propranolol and diazepam on autonomous reactions to different stressors.

1. To evaluate the influence of beta-blockers and minor tranquilizers on autonomous stress response, 40 healthy subjects selected with regard to personality traits were randomly assigned to 5 groups. 2. Mental arithmetic induced the most pronounced increase in heart rate (HR), blood pressure and epinephrine secretion. 3. Beta-blockers reduced HR increases due to mental stress, whereas the minor tranquilizer reduced skin conductance level throughout the whole trial. 4. Our data provide evidence that different structured situations induce specific response patterns that are differentially modified by beta-blockers and minor tranquilizer.

Adrenergic beta-Antagonists↗
PubMed1989

Lipoxygenase inhibitors suppress formation of tumor necrosis factor in vitro and in vivo.

The LPS induced synthesis of tumor necrosis factor in macrophage cultures, as determined in a fibroblast cytolysis assay was found to be effectively blocked by inhibitors of lipoxygenases. Likewise, the presence of tumor necrosis factor in serum of D-galactosamine sensitized mice after challenge with endotoxin was suppressed by the lipoxygenase inhibitors. Indomethacin, a blocker of cycclooxygenase was neither in vivo nor in vitro effective in the prevention of the endotoxin-induced synthesis of TNF. From LPS-treated macrophages we were able to isolate 13-hydroxylinoleic acid, a lipoxygenase product, which is significantly increased after LPS treatment of the cells, covalently bound to cellular constituents and may, therefore, be possibly involved in the formation of TNF.

Animals↗
PubMed1988

Chromosome translocation (2;13)(q37;q14) in a disseminated alveolar rhabdomyosarcoma.

Chromosome analysis of tumour cells in the bone marrow of a 13.5-year-old girl (without a primary tumour) revealed a pseudo-diploid or pseudo-tetraploid karyotype with a translocation involving the long arms of chromosomes 2 and 13: t(2;13)(q37;q14). This finding enabled the diagnosis of a disseminated alveolar rhabdomyosarcoma (RMS) to be established. The patient was treated by cytotoxic chemotherapy, went into complete remission, but died of relapse 14 months after diagnosis. As several cases with this translocation have been described recently, this additional report confirms that t(2;13) is specific for the alveolar subtype of RMS.

Adolescent↗
PubMed1987

Increased 13-hydroxyoctadecadienoic acid content in lipopolysaccharide stimulated macrophages.

Endotoxin-stimulated mouse peritoneal macrophages were found to contain 13-hydroxyoctadecadienoic acid, which was released upon alkaline hydrolysis of the cells. Compared to untreated cells, incubation with LPS increased the content of 13-hydroxyoctadecadienoic acid in macrophage hydrolysates to about 8-fold. Analysis of the material on chiralphase HPLC revealed that it consisted prevalently of 13(S)-hydroxyoctadecadienoic acid. This indicates its enzymatic origine.

Animals↗
PubMed1987

Routine clinical determination of carotene, vitamin E, vitamin A, 25-hydroxy vitamin D3 and trans-vitamin K1 in human serum by straight phase HPLC.

A universal extraction procedure is described for fat-soluble vitamins in human serum. Methods are presented for routine quantitative analysis by isocratic straight phase HPLC with UV-detection of (alpha + beta)-carotene, vitamin E (alpha-tocopherol) and vitamin A (all-trans-retinol) in one single run, and of vitamin K1 (trans-phylloquinone) and 25-hydroxy vitamin D3 after sample clean-up using disposable reversed-phase cartridges. The limits of detection, precisions and selectivities of the developed assays are shown to be satisfactory after more than three years' experience. The routine clinical determination of fat-soluble vitamins can be performed in less than 5 mL of serum. Analyses of external quality control and randomly taken outpatient samples are shown to be of great value in assessing laboratory performance.

Calcifediol↗
PubMed1987

Metabolism of L-glyceraldehyde 3-phosphate in Escherichia coli.

When either 3H-labeled L-glyceraldehyde or 3H-labeled L-glyceraldehyde 3-phosphate (GAP) was added to cultures of Escherichia coli, the phosphoglycerides were labeled. More than 81% of the label appeared in the backbone of the phosphoglycerides. Chromatographic analyses of the labeled phosphoglycerides revealed that the label was normally distributed into phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. These results suggest that L-glyceraldehyde is phosphorylated and the resultant L-GAP is converted into sn-glycerol 3-phosphate (G3P) before being incorporated into the bacterial phosphoglycerides. Cell-free bacterial extracts catalyzed an NADPH-dependent reduction of L-GAP to sn-G3P. The partially purified enzyme was specific for L-GAP and recognized neither D-GAP nor dihydroxyacetone phosphate as a substrate. NADH could not replace NADPH as a coenzyme. The L-GAP:NADPH oxidoreductase had an apparent Km of 28 and 35 microM for L-GAP and NADPH, respectively. The enzyme was insensitive to sulfhydryl reagents and had a pH optimum of approximately 6.6. The phosphonic acid analog of GAP, 3-hydroxy-4-oxobutyl-1-phosphonate, was a substrate for the reductase, with an apparent Km of 280 microM.

Alcohol Oxidoreductases↗