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Biomedical subjects

K Richter

Publications and source records attributed to K Richter.

At least 145 records · Page 8Linked to original sources
PubMed1997

Expression of a chemotactic cytokine (MCP-1) in cerebral capillary endothelial cells in vitro.

A full-length cDNA encoding the porcine monocyte chemoattractant protein-1 (pMCPC-1) was isolated from growth-stimulated porcine cerebral capillary endothelial cells (cEC); the pMCP-1 cDNA showed 89% identity to human MCP-1 and was isolated by use of subtractive hybridization and differential screening of two phenotypically different sub-populations of cloned cEC. pMCP-1 was abundantly expressed in cEC grown in the presence of FCS, ECGF and heparin whereas lower expression was observed in cEC kept in FCS-supplemented medium only. As shown by Northern blot analysis, no pMCP-1 transcripts were present in total RNA derived from freshly isolated brain capillaries, large brain vessels or whole brain homogenate. MCP/JE expression was also demonstrated in ECGF/heparin-treated murine cEC. Astrocytes and smooth muscle cells grown in FCS-supplemented medium did not show MCP-1 expression. Treatment of porcine cEC with TNF-alpha increased pMCP-1 mRNA levels in a dose-dependent manner. These data further support the notion that cerebral capillary endothelial cells actively participate in processes of CNS host defense.

Amino Acid Sequence↗
PubMed1997

Selective reduction for multifetal pregnancy. Early opinions revisited.

Multifetal pregnancy reduction has emerged as a staple of infertility therapy. With increasing utilization of aggressive infertility therapies, thousands of couples have been able to achieve pregnancies who otherwise would not have, but an increasing number and proportion of patients have multifetal pregnancies. Multifetal pregnancy reduction (MFPR) has been shown to be a safe and effective treatment for reducing the number of pregnancies, thereby reducing both perinatal morbidity and mortality in resultant pregnancies. The world experience suggests that the risks of MFPR are directly related to the starting number of fetuses but that in the majority of instances, healthy children can be achieved.

Ethics, Medical↗
PubMed1996

Determination of scopolamine in human serum by gas chromatography-ion trap tandem mass spectrometry.

The objective of this study was to develop a very sensitive and selective method for the determination of scopolamine in serum with a rapid and simple sample preparation. A capillary column gas chromatographic-ion trap tandem mass spectrometric technique has been applied. Scopolamine and the internal standard mexiletine were extracted from serum samples and cleaned up by using a single step liquid-liquid extraction. Derivatization was carried out using 2,2,2-trifluoro-N-methyl-N-trimethylsilylacetamide. The mass spectrometer was operated with positive ions in the selected reaction mode with chemical ionisation using methane. The sum of peak height of two daughter ions was used for quantification. The detection limit was 50 pg/ml in serum.

Cholinergic Antagonists↗
PubMed1996

New sensitive method for the determination of hydrochlorothiazide in human serum by high-performance liquid chromatography with electrochemical detection.

A HPLC method with a very sensitive electrochemical detection has been developed for determining the diuretic agent hydrochlorothiazide (HCT) in serum of volunteers to whom a single dose of the fixed combination of 12.5 mg HCT and 25 mg triamterene was administered. In the present method samples (0.2 ml serum, pH 7) were purified by extraction of HCT into 5 ml tert.-butyl-methyl ether. The separated organic phase was spiked with p-aminobenzoic acid (PABA) standard. The separation was performed on a reversed-phase C18 column using phosphate buffer-acetonitrile (90:10). A coulometric cell was used to measure HCT and an ultraviolet detector for PABA. The limit of quantitation for serum samples of only 200 microliters was 5 ng/ml (i.e. 60 pg HCT/injection) with a good reproducibility (1-8%). Short retention times were found: 1.2 min for PABA and 5.8 min for HCT.

4-Aminobenzoic Acid↗
PubMed1996

Detection of diffuse breast cancers with a new sonographic method.

The presentation of diffuse cancers detected with a new sonographic method is described. It uses compression of the breast in positions which are used in mammography and a reflecting metallic plate to look for the presence of breast lesions. Changes in reflectivity and velocity are imaged on this reference structure and can be compared with appearance of the reference structure behind normal tissue. Detectability and sonographic appearance are reported in 13 diffuse malignancies and one diffuse benign lesion that had been found among 89 malignant and 83 benign lesions in 151 preoperative patients. Ten breast cancer patients who had been treated with breast-conserving surgery and radiation therapy were also examined sonographically as a model for diffuse changes of the breast parenchyma.

Adult↗
PubMed1996

Ultrastructural localization of glycogen phosphorylase predominantly in astrocytes of the gerbil brain.

The localization of glycogen phosphorylase in gerbil brain was determined by immunoelectron microscopy using the pre-embedding peroxidase technique. Electron-dense granular reaction product of peroxidase activity was observed in astrocytes of all brain regions examined (cerebral cortex, striatum, cerebellar cortex, hippocampal formation, corpus callosum, mesencephalic trigeminal nucleus). The reaction product was distributed in a diffuse pattern throughout the cytoplasmic matrix of perikarya and processes; sometimes the nucleus of labeled astrocytes also contains immunopositive material. The light microscopically visible glycogen phosphorylase immunoreactivity associated with capillaries could be characterized as a staining of astrocytic endfeet ensheathing capillaries. Endothelial cells and pericytes were never labeled. In addition to astrocytes, ependymal cells also presented immunopositive material in their cytoplasm. On the other hand, no reaction product was observed in cells identified as oligodendroglia or microglia. Neurons (with the exception of neurons of the mesencephalic trigeminal nucleus), their processes, and their synaptic endings were free of reaction product. In the neuropil we frequently observed immunopositive glial processes adjacent to synaptic structures. This intimate spatial relationship may be interpreted as a morphological sign of a metabolic interaction. The data support the hypothesis that astroglia play a key role in glycogen metabolism and energization of the brain.

Animals↗
PubMed1996

Pharmacokinetic/pharmacodynamic modeling of cortisol suppression after oral administration of fluocortolone.

Fluocortolone is a potent corticosteroid used orally for the treatment of rheumatic diseases, asthma, and immunosuppression. A clinical study of nine healthy volunteers was conducted to determine the pharmacokinetics and cortisol suppression after administration of single oral doses of 20 mg, 50 mg, and 100 mg of fluocortolone. Blood samples were collected at 8:00 AM, 12:00 PM, and 4:00 PM on the day before treatment, and 0, 0.5, 1, 2, 3, 4, 6, 8, 12, 24, 28, 32, 48, 52, and 56 hours after administration of the drug. Concentrations of fluocortolone and cortisol were measured in plasma by a reversed phase high-performance liquid chromatography system. Cortisol suppression was chosen as the pharmacodynamic parameter. Total concentrations were converted into unbound concentrations using a two-protein, one-ligand equation. The unbound concentrations were fitted using a one-compartment body model equation with first-order absorption. A linear release-rate model was used to characterize the cortisol data. The data were fitted using a common E50 value of 0.95 +/- 0.22 ng/mL for the mean data. The value of E50 was in close agreement with the prediction based on relative glucocorticoid receptor affinity.

Administration, Oral↗
PubMed1996

The Xenopus homologue of hepatocyte growth factor-like protein is specifically expressed in the presumptive neural plate during gastrulation.

Using a RT-PCR approach, we were able to isolate a cDNA encoding the Xenopus homologue of hepatocyte growth factor-like protein, which we have termed accordingly Xhl. The deduced Xhl protein consists of 717 amino acids, contains four putative kringle domains and a serine protease-like domain characteristic for mammalian HGF and HGF-like protein. The mRNA of Xhl is exclusively expressed in the midline of the prospective neural plate during the period of neural induction, only. Ectopic expression of Xhl causes a 'spina bifida'-like phenotype with enlargement of neural tissue. Activation of Xhl mRNA transcription can be induced by delayed reaggregation of animal caps and appears to require vertical rather than planar signals from the organizer. These data suggest that Xhl is involved in the formation of the embryonic nervous system of Xenopus.

Amino Acid Sequence↗
PubMed1996

Comparison of slam-freezing and high-pressure freezing effects on the DNA cholesteric liquid crystalline structure.

Using in parallel electron microscopy of ultrathin frozenhydrated sections and freeze-fracture replicas, we compare the ultrastructural consequences of two freezing techniques: slam-freezing at liquid helium temperature and high-pressure freezing, on a model system, the DNA cholesteric liquid crystalline phase. Both freezing techniques are able to vitrify DNA liquid crystalline solutions containing up to 85% water, but induce structural rearrangements of the molecular organization. The cholesteric structure is preserved by the slam-freezing method despite the formation of periodic distortions induced by the mechanical compressive stress. In contrast, high-pressure freezing does not preserve the structure of the liquid crystal: the long-range cholesteric stratification disappears, and the local continuous twist between molecules is modified. These results show that vitrification, though necessary, may not be a sufficient token of preservation of the native state of hydrated materials. We discuss the possible origins of the molecular rearrangements that have time to occur in the specimens as a result of the low freezing rate permitted by the high-pressure freezing process.

Crystallization↗
PubMed1996

Differentiation of breast lesions by measurements under craniocaudal and lateromedial compression using a new sonographic method.

RATIONALE AND OBJECTIVES: The authors differentiate breast lesions on sonography by measurements in two compression states that are perpendicular to each other. METHODS: Diameters of 100 breast lesions were measured preoperatively under lateromedial and craniocaudal compression with a new sonographic method. This method uses mammography-identical positioning of the breast and a reference structure for detection of changes of sound amplitude and velocity by through transmission of lesions. Sizes parallel to sound propagation were corrected for abridgement by increased velocity within some lesions. For each lesion, an average length and breadth was calculated by adding sizes parallel and perpendicular to sound propagation in the two compression states and dividing it by 2. An average ratio was calculated for each lesion by dividing the average size perpendicular to sound propagation by the corrected average size along sound propagation. After obtaining histopathologic results, a threshold of ratios and other features that might help differentiate benign from malignant lesions were studied. RESULTS: Ninety-six percent of the malignant lesions appeared with ratios < or = 1.2, whereas 92% of the benign lesions had a ratio > 1.2. Further differentiation is possible by observation of velocity in lesions with ratios > 1.2. CONCLUSIONS: Examination of lesions in two compression states that are perpendicular to each other allows discrimination of benign and malignant masses by measurements in most patients.

Adult↗
PubMed1996

Determinants of migration values and expectations in rural Thailand.

"Based on the argument that values and expectations underlie behavioral motives, this study explores the determinants of migration-related values and expectations, and whether they are intervening factors in explaining intentions to move among residents of rural northeast Thailand. Data from the 1992 National Migration Survey of Thailand identify four migration-related value-expectancy dimensions: income, affiliation, stimulation, and comfort. Logistic regression analysis shows that landownership and being married are associated with higher expectations, while a diversified village economy, a village economy development program, and a younger and extended household structure are associated with lower expectations of attaining valued goals in the local rural village. The analysis also shows that value-expectancy concepts are only partial intervening explanations for intentions to move or stay."

Asia↗
PubMed1996

Gender, values, and intentions to move in rural Thailand.

"This article explores gender differences in the intentions to move among a sample of young adults in rural northeastern Thailand. Based on the value-expectancy framework of migration decisionmaking, an explanatory model is tested which includes migration-related value measures along with individual, household and community-level determinants of both intentions to move and change in intentions to move. Multinomial logistic regression results based on data from the 1992 Thailand National Migration Survey provide some support for the hypothesis of gender-specific determinants of both intentions to move and the reconsideration of migration intentions. For men, value measures of affiliation and comfort, social networks, the presence of young children in the family, and land holdings are significant determinants of migration decisionmaking; for women income and comfort values, the presence of elderly persons in the household, community size, and crop losses are the salient factors."

Asia↗
PubMed1996

[Prevention of osteoporosis: estrogen substitution paradigm].

There is an increasing belief among most physicians that hormone replacement therapy (HRT) is unquestionable efficacious to prevent osteoporotic fractures in women after the menopause. However, an analysis of the studies which are regarded as efficacy proof of HRT concerning the prevention of hip fractures--as the most important manifestation of osteoporosis--shows that the data are weaker than generally assumed: there are no randomised trials with regard to hip fracture prevention by HRT and the protective effect which is seen in the observational studies is inversely related to the methodical state of the respective type of study. Consequently, a bias cannot be excluded, while the so-called 'selection-by-health'-bias could play an outstanding role. For the efficacy proof of a treatment randomised controlled trials cannot be replaced by results of observational studies, however impressive they may be.

Bias↗
PubMed1996

Aspects of cryofixation and cryosectioning for the observation of bulk biological samples in the hydrated state by cryoelectron microscopy.

Cryoelectron microscopy allows the observation of hydrated samples at high spatial resolution, and it would be of great interest in biology to apply this method to cells and tissues. However, because of technical problems, the cryo-observation of frozen hydrated ultrathin sections of bulk material has not become an established method. The major limitations are due to the difficulty of achieving the vitrification of such material, and the structural deformation caused by ultrathin sectioning: 1. The vitrification of cells in a physiological environment requires high-pressure freezing. However, new results suggest that the pressure may alter the ultrastructure of the sample. 2. Cryosectioning compresses structures in the cutting direction about 40%. This deformation does not necessarily destroy the character of macromolecular assemblies, but since it depends on the properties of the material, internal standards cannot be used to correct for the deformation of all the structures in a cell.

Animals↗
PubMed1995

Transcription factors Stat3 and Stat5b are present in rat liver nuclei late in an acute phase response and bind interleukin-6 response elements.

Proteins binding at the interleukin-6 response element of the rat alpha 2 macroglobulin gene were purified by a combination of chromatographic procedures including binding site-specific DNA-affinity chromatography as the principal step. Three polypeptides of 92, 91, and 86 kDa were enriched approximately 6,300-fold from nuclei of rat livers excised 12 h after the induction of an experimental acute phase response. Amino acid sequence analysis identified the 86- and 91-kDa species as two forms of the transcription factor Stat3 and the 92-kDa species as the factor Stat5b. This identification was confirmed by gel mobility shift-supershift experiments using specific antisera for Stat3 and Stat5. Unexpectedly, activated Stat5 was also detected in the nuclei of untreated control rats. cDNA clones representing Stat3 and two isoforms of Stat5b were isolated from a cDNA library prepared with mRNA from rat livers excised at the peak of an experimental acute phase response. Full-length Stat5b, predicted from cDNA, consisted of 786 amino acids, while the variant Stat5b delta 40C lacked 41 amino acids at the COOH terminus. The amino acid sequence of rat Stat5b showed 26.7% overall identity with rat Stat3, 87.3% with sheep Stat5a, 92.5% with murine Stat5a, and 98.7% with murine Stat5b.

Acute-Phase Proteins↗
PubMed1995

Brevican, a chondroitin sulfate proteoglycan of rat brain, occurs as secreted and cell surface glycosylphosphatidylinositol-anchored isoforms.

cDNA clones encoding proteins related to the aggrecan/versican family of proteoglycan core proteins have been isolated with antisera against rat brain synaptic junctions. Two sets of overlapping cDNAs have been characterized that differ in their 3'-terminal regions. Northern analyses with probes derived from unique regions of each set were found to hybridize with two brain-specific transcripts of 3.3 and 3.6 kilobases (kb). The 3.6-kb transcript encodes a polypeptide that exhibits 82% sequence identity with bovine brevican and is thought to be the rat ortholog of brevican. Interestingly, the polypeptide deduced from the open reading frame of the 3.3-kb transcript is truncated just carboxyl-terminal of the central domain of brevican and instead contains a putative glypiation signal. Antibodies raised against a bacterially expressed glutathione S-transferase-brevican fusion protein have been used to show that both soluble and membrane-bound brevican isoforms exist. Treatment of the crude membrane fraction and purified synaptic plasma membranes with phosphatidylinositol-specific phospholipase C revealed that isoforms of brevican are indeed glycosylphosphatidylinositol-anchored to the plasma membrane. Moreover, digestions with chondroitinase ABC have indicated that rat brevican, like its bovine ortholog, is a conditional chondroitin sulfate proteoglycan. Immunohistochemical studies have shown that brevican is widely distributed in the brain and is localized extracellularly. During postnatal development, amounts of both soluble and phosphatidylinositol-specific phospholipase C-sensitive isoforms increase, suggesting a role for brevican in the terminally differentiating and the adult nervous system.

Amino Acid Sequence↗