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Biomedical subjects

D de Wit

Publications and source records attributed to D de Wit.

11 recordsLinked to original sources
PubMed1997

Analysis of two pharmacologically predicted endothelin B receptor subtypes by using the endothelin B receptor gene knockout mouse.

1. This study was performed to clarify whether the endothelin (ET) receptor subtypes mediating two pharmacologically heterogeneous response to ETH receptor agonists in normal mice are the product(s) of a single ETB receptor gene. 2. Vasodilator responses to sarafotoxin S6c (S6c) in the thoracic aorta and contractile responses to ET-1 and IRL1620 in the stomach were examined in tissues from normal and ETB receptor gene knockout mice, in the absence and presence of an ETA receptor antagonist, BQ-123, or an ETA/ETB receptor antagonist, PD142893. 3. In the normal mouse aorta precontracted with phenylephrine, S6c (0.1-100 nM) caused concentration-dependent relaxations (pD2 = 8.4). BQ-123 had no effect on these responses. However, PD142893 almost abolished the relaxations induced by 0.1-300 nM S6c. 4. In aortae taken from ETB receptor gene knockout mice, S6c up to 1 microM failed to cause relaxations, confirming that ETB receptors are involved in mediating this response. 5. In normal mouse gastric fundus, 0.1 nM-1 microM ET-1, S6c or IRL1620 caused dose-dependent, BQ-123-insensitive contractions, which were much more resistant to PD142893 than S6c-induced relaxations of the aorta. The pD2 values for S6c in the absence and presence of PD142893 (10 microM) were 8.12 +/- 0.11 and 7.70 +/- 0.11, respectively. 6. In the gastric fundus of the ETB receptor gene knockout mouse, S6c and IRL1620 caused no contractions. ET-1 (0.1 nM-1 microM) caused contractions sensitive to both BQ-123 and PD142893, indicating that only ETA receptors mediate ET-1-induced contractions of the knockout mouse gastric fundus. 7. Since both the PD142893-sensitive vasodilator response of the aorta and the PD142893-resistant contractile response of the gastric fundus to S6c were completely absent in the ETB receptor gene knockout mouse, we conclude that the two pharmacologically heterogeneous responses to S6c are mediated by receptors derived from the same ETB receptor gene.

Animals↗
PubMed1996

Single crystals of inulin.

Lamellar crystals of inulin were grown by crystallizing sharp fractions of low molecular weight inulin from dilute aqueous ethanol solutions. The crystals were analyzed using three-dimensional electron diffraction and X-ray powder diagrams. Two crystalline polymorphs were observed, depending on the hydration conditions: a hydrated form which indexed on an orthorhombic unit cell, with space group P2(1)2(1)2(1) and with cell dimensions of a = 1.670 nm, b = 0.980 nm and c (chain axis) = 1.47 nm, together with a pseudo-hexagonal semi-hydrated form with unit cell parameters a = 1.670 nm, b = 0.965 nm and c (chain axis) = 1.44 nm. These parameters, together with the density data, indicate that inulin crystallizes along a pseudo-hexagonal six-fold symmetry with an advance per monomer of 0.24 nm. The difference between the hydrated and the semi-hydrated unit cells does not seem to correspond to any change in the conformation of inulin, but rather to a variation in water content.

Carbohydrate Conformation↗
PubMed1996

Creative infection control.

In spite of the widespread use of educational programmes, there still remains a low staff knowledge and non-compliance of infection control policies. In order to overcome these problems we have attempted to increase interest and raise awareness of infection control by introducing a motivational programme termed Creative Infection Control. Some of the activities are illustrated and are loosely structured, and rely largely on humour and intergroup competition. These methods are based on sound psychological principles with an emphasis on adult-learning theory. Objective measures indicate that such programmes can significantly influence infection control outcomes.

Adult↗
PubMed1995

The bacterial DNA content of mouse organs in the Cornell model of dormant tuberculosis.

SETTING: The Cornell model of murine tuberculosis has proved useful for demonstrating and studying dormancy. However, it has not previously been used to investigate the molecular aspects of dormancy. OBJECTIVE: To obtain a profile of the amount of Mycobacterium tuberculosis DNA at various stages of the Cornell model. DESIGN: BALB/C mice were infected intravenously with 2.7 x 10(6) cfu M tuberculosis strain H37Rv; they were left for two weeks, treated for 14 weeks with isoniazid and pyrazinamide and left untreated for a further 14 weeks. Spleens and lungs at start of treatment and at 8, 12, 14, 18, 24 and 28 weeks thereafter were examined by culture, and DNA in tissue homogenates was quantitated by polymerase chain reaction (PCR) and dot blot hybridisation. RESULTS: Culture and quantitative PCR estimated initial bacillary content at about 10(7) per organ. Thereafter, organ cultures rapidly declined and were usually negative between 14 and 28 weeks. However, during this period quantitative PCR consistently estimated about 5.5 log10 bacilli equivalents in spleens and lungs. Dot blot hybridisation sensitive to about 10 ng bacillary DNA was usually positive pretreatment and occasionally during and after treatment, hence confirming the PCR results. CONCLUSIONS: There is persistence of significant quantities of M. tuberculosis DNA throughout the various stages of the model. This may represent dead bacilli, free DNA or dormant forms.

Animals↗
PubMed1993

DNA analysis demonstrates that mycococcus forms are not mycobacteria.

Previous experimental evidence has suggested that the mycobacteria may exist in morphological forms other than the well characterised acid-fast bacillus. However none of these studies have been able to show conclusively that these variant forms are derived from the mycobacteria and therefore much debate has centered around the exact nature of these organisms. In this study we have examined stored cultures of the mycococcus form of Mycobacterium bovis BCG and M. phlei which were prepared by Csillag in 1972 and 1969. Restriction fragment patterns of the DNA of the variant forms and the parent mycobacteria were not similar and chromosomal DNA from the parent mycobacteria did not hybridise with the DNA of the variant forms. Furthermore biochemical studies indicate that the variant forms are environmental contaminants. Although this study shows conclusively that the mycococcus is not derived from the mycobacteria, we believe that the search for variant morphological or metabolic forms of the mycobacteria should remain an active area of investigation, but that no study should be considered complete without the full use of newer molecular technology.

Animals↗
PubMed1992

The periodate oxidation of sucrose in aqueous N,N-dimethylformamide.

Sucrose has been oxidized with sodium periodate in 0-50% aqueous N,N-dimethylformamide (DMF). In 50% aqueous DMF the reaction is selective for the glucose ring, yielding a dialdehyde. The increased selectivity is not due to conformational factors but is ascribed to the dissociation of water from cyclic periodate ester species which makes the reaction via the acyclic ester on fructose unfavourable.

Carbohydrate Sequence↗
PubMed1992

A comparative study of the polymerase chain reaction and conventional procedures for the diagnosis of tuberculous pleural effusion.

Preliminary reports by ourselves and others suggest that amplification of mycobacterial DNA by the polymerase chain reaction (PCR) is a sensitive and rapid diagnostic test for tuberculosis. We recently described a PCR assay with a 336 bp repetitive sequence specific for Mycobacterium tuberculosis as the DNA target, which gave encouraging results in culture-positive smear-negative clinical specimens. In the present prospective study of patients with pleural effusions we compared PCR of the pleural fluid with conventional procedures. 84 adult patients with pleural effusions were divided into 4 groups. In group A (44 patients), M. tuberculosis was detected by culture of pleural fluid, pleural biopsy or extrapleural source. In group B (6 patients), tuberculous infection was confirmed by histology (group A excluded). Group C (3 patients) had clinical evidence of tuberculosis. Group D (31 patients) had no evidence of active M. tuberculosis infection. Analysis of the pleural fluid confirmed a sensitivity for PCR of 81%. The sensitivity of pleural fluid culture, culture of pleural biopsy, and histology of biopsy was 52.8%, 69.8% and 77.3% respectively. There were however 7 PCR positive results within group D; 6 of these were in patients with malignant effusions. We conclude that for the diagnosis of M. tuberculosis PCR is more sensitive than laboratory culture as determined by the analysis of pleural fluids. Positive PCR results among patients with malignant effusions may be false-positives or the result of latent tuberculous infections. PCR should remain an investigational procedure until prospective studies in high and low prevalence areas have critically evaluated the specificity of the assay.

Adult↗
PubMed1988

Monoclonal antibodies directed against the sexual binding site of Chlamydomonas eugametos gametes.

Monoclonal antibodies were raised against the mt- sexual agglutinin of Chlamydomonas eugametos gametes. Those that blocked the agglutination site were selected. They were divided into two classes dependent upon whether they gave a weak (class A) or clear positive (class B) reaction with mt- flagellar membranes in an ELISA and an indirect immunofluorescence test using glutaraldehyde-fixed mt- gametes. Class A antibodies were shown to be specific for the agglutinin in an extract of mt- gametes, based on results from immunoblotting, immunoprecipitation, affinity chromatography, and the absence of a reaction with nonagglutinable cells. Surprisingly, class A mAbs also recognized two mt+ glycoproteins, one of which is the mt+ agglutinin. Class B antibodies were shown to bind to several glycoproteins in both mt- and mt+ gametes, including the mt- agglutinin. Fab fragments from class A mAbs blocked the sexual agglutination process, but those from class B did not, even though the parent antibody did. We conclude that the class A epitope lies in or close to the agglutination site of the mt- agglutinin, whereas the class B epitope lies elsewhere on the molecule. We also conclude that the mt- agglutinin is the only component on the mt- flagellar surface directly involved in agglutination. Class A mAbs were found to elicit several reactions displayed by the mt+ agglutinin. They bound to the mt- agglutinin on gamete flagella and induced most of the reactions typical of sexual agglutination, with the exception of flagellar tip activation. None of these reactions was induced by Fab fragments. High concentrations of class A mAbs completely repressed the sexual competence of live mt- gametes, but low concentrations stimulated cell fusion.

Agglutination↗