PubMed Health⌕ Search

Biomedical subjects

J G Williams

Publications and source records attributed to J G Williams.

At least 19 recordsLinked to original sources
PubMed1992

Chemotactic sorting to cAMP in the multicellular stages of Dictyostelium development.

Dictyostelium transformants that overproduce the extracellular form of cyclic nucleotide phosphodiesterase and so accumulate a reduced amount of cAMP are blocked in development after aggregation in the form of a tight mound, prior to formation of the apical tip. In such mounds, prespore cell differentiation is repressed, and the apical accumulation of prestalk cells is greatly retarded. When a source of cAMP is placed below the arrested mounds, prestalk cells that would normally migrate in an apical direction instead sort downwards to the substratum. Thus, by acting as the chemoattractant that draws prestalk cells to the apex, cAMP signaling directs the formation of a patterned structure.

Animals↗
PubMed1992

Cloning and characterization of the Dictyostelium discoideum rasG genomic sequences.

A Dictyostelium discoideum genomic DNA clone containing the ras-related gene, rasG was isolated using the rasG cDNA as a probe. The genomic clone encompasses the entire coding region of the gene and 1.5 kb of 5' flanking region. The rasG gene contains a single intron as determined by sequence comparison with the cDNA, whereas the highly related rasD gene contains three introns. Primer extension analysis showed that transcription of the rasG gene initiates at multiple sites. Sequence analysis of the 5' flanking region of the gene revealed a stretch of thymine residues upstream from the transcription start sites but there is no evidence for a TATA box sequence.

Animals↗
PubMed1992

A G-rich sequence element common to Dictyostelium genes which differ radically in their patterns of expression.

Removal of a G-rich element from the DIF-inducible, prestalk-, and stalk-specific ecmB gene reduces expression but cell-type specificity is retained. The ecmB element will functionally substitute for a homologous sequence upstream of CP2, a cAMP-inducible gene and is bound by GBF, the factor which interacts with the CP2 G box. These results suggest that the G box may play a similar stimulatory role in these two independently regulated genes where it presumably interacts with different ancillary promoter elements.

Animals↗
PubMed1992

Absorption of non-haem iron in normal women measured by the incorporation of two stable isotopes into erythrocytes.

1. Iron absorption has been quantitatively measured as the incorporation of physiological doses of stable iron isotopes into erythrocytes. Five milligrams of 57Fe (orally) and 250 micrograms of 58Fe (intravenously) were given to five healthy women on 2 consecutive days. Fourteen days later the changes in the 57Fe/56Fe and 58Fe/56Fe ratios in the erythrocytes of each subject were measured using an inductively coupled plasma mass spectrometer. Isotope ratios were also measured in two subjects who were not given any enriched isotope. Concomitant measurements of plasma volume using a dye-dilution technique enabled the estimation of body iron mass and the calculation of iron absorption. 2. The mean coefficients of variation for the 57Fe/56Fe ratio and the 58Fe/56Fe ratio were 0.22% and 0.47%, respectively. This precision allowed enrichments of basal ratios to be reliably detected in all cases. The mean change in the 57Fe/56Fe ratio was 0.00116 (SD 0.00052, P < 0.001) and the mean change in the 58Fe/56Fe ratio was 0.00035 (SD 0.00004, P < 0.001). Control subjects showed no enrichment. 3. The calculated iron absorption ranged from 10% to 34%, and the amount of absorption was related to the iron stores of the subjects. Percentage iron absorption was identical when estimates of the plasma volume (derived from a body mass equation) were used instead of the plasma volume determined by dye-dilution measurements. Incorporation of intravenous iron into erythrocytes was on average 81% (range 68-93%). 4. The method is especially applicable to the study of iron absorption during pregnancy when incorporation into erythrocytes cannot be predicted.

Absorption↗
PubMed1992

Histamine H2-receptor antagonists in peptic ulcer disease. Efficacy in healing peptic ulcers.

Duodenal ulcer healing depends on the degree and length of inhibition of gastric secretion and upon the duration of therapy, while gastric ulcer healing is dependent mainly on the duration of therapy. Currently marketed doses of the histamine H2-receptor antagonists heal between 77 and 92% of duodenal ulcers at 4 weeks, and adjuvant treatment to eradicate Helicobacter pylori increases this rate. Once-daily administration is as effective as more frequent dosing regimens and may even result in higher healing rates. Gastric ulcers heal more slowly, but 75 to 88% of ulcers heal after 8 weeks of treatment. While newer more potent acid suppressors such as omeprazole heal ulcers slightly more quickly, the H2-receptor antagonists have an unparalleled safety record of over 15 years. It is unlikely that the prostaglandin analogues can improve on the efficacy of the H2-receptor antagonists with as low an incidence of side effects.

Drug Administration Schedule↗
PubMed1992

Randomised cross-over comparison of five inhaler systems for bronchodilator therapy.

The pharmacological efficacy of beta-2 agonists such as bronchodilators is well established, yet many patients fail to obtain optimum benefit from conventional metered-dose inhalers. This is usually because of difficulty in achieving adequate co-ordination between activation of the aerosol and inhalation. To some extent this problem can be alleviated by detailed personal instruction and re-instruction, but the medical or paramedical staff needed to do this may be unavailable and in any case their time is expensive. To increase the benefit obtained from bronchodilators, therefore, pharmaceutical companies have produced a variety of devices, eg, large-volume (750 ml) spacers (Nebuhaler, Volumatic) which enclose a cloud of aerosol, obviating the need for actuation-inhalation co-ordination, and breath actuated dry-power inhalers with (Rotahaler, Diskhaler) or without (Turbohaler) carrier powders. Subsequent compliance with treatment is dependent upon the acceptability of the inhaler device to the patient.

Adolescent↗
PubMed1992

Collecting, communicating and using information: the educational issues. A report from the Royal College of Physicians Committee on Medical Information Technology.

Few of the major advances in information science and technology have yet been successfully introduced in health care. Their implementation could improve both quality of care and the working environment of clinicians, but this will not be achieved by investing in hardware and software alone. Investment in education is also required.

Attitude to Computers↗
PubMed1992

Ketoconazole inhibits alveolar macrophage production of inflammatory mediators involved in acute lung injury (adult respiratory distress syndrome).

BACKGROUND: Acute inflammatory lung injury (adult respiratory distress syndrome [ARDS]) causes significant morbidity and death in surgical patients. The alveolar macrophage elaborates proinflammatory mediators implicated in acute pulmonary injury. The macrophage products, leukotriene B4 (LTB4), thromboxane A2 (TXA2), and procoagulant activity (PCA), initiate inflammatory cascades that lead to microvascular thrombosis and neutrophil infiltration, two common features of ARDS. One potential method of preventing or attenuating lung injury is to inhibit the production of inflammatory mediators. Preliminary studies indicate that ketoconazole, known primarily for its antifungal properties, may prevent ARDS. METHODS: LTB4, TXB2, and PCA production by rabbit alveolar macrophages was measured after treatment with endotoxin or Ca ionophore and ketoconazole or selective 5-lipoxygenase (MK 886) and thromboxane synthetase (imidazole) inhibitors. RESULTS: Ketoconazole significantly inhibits alveolar macrophage production of LTB4, TXB2, and PCA. Ketoconazole inhibition of PCA is independent of effects on 5-lipoxygenase and thromboxane synthetase. CONCLUSIONS: Ketoconazole inhibition of alveolar macrophage proinflammatory mediators may be of benefit in preventing ARDS by minimizing neutrophil infiltration and microvascular thrombosis. Inhibition of 5-lipoxygenase and thromboxane synthetase, without affecting cyclooxygenase, may offer a selective advantage by allowing production of other homeostatic eicosanoids.

Animals↗
PubMed1979

Characterization and transcription analysis of a cloned sequence derived from a major developmentally regulated mRNA of D. discoideum.

The plasmid pDd 812 contains a portion of a poly(A)+ RNA sequence isolated from developing cells of the cellular slime mold Dictyostelium discoideum (Williams and Lloyd, 1979). The poly(A)+ RNA complementary to this plasmid shows an increase in concentration during the first 4 hr of development followed by a decrease in concentration during the following 4 hr. This RNA is very abundant after 3-4 hr of development, constituting at least 2% of the poly(A)+ RNA population. In this study, we demonstrate that this poly(A)+ RNA is an mRNA sequence by translating the RNA complementary to pDd 812 in a heterologous system. The mRNA directs the synthesis of a major polypeptide of 33,000 daltons and a minor polypeptide of 31,000 daltons. We have used the plasmid DNA immobilized on filters to analyze the transcription of this RNA sequence in isolated nuclei. The amount of transcript synthesized in nuclei isolated at various stages of development which was complementary to pDd 812 changed in the same way as did the cytoplasmic concentration of this RNA--that is, maximal transcription occurred after 3-4 hr of development. Because this result was observed using labeling periods as short as 5 min, we believe that this change is unlikely to reflect a change in the rate of processing of RNA. We interpret these results to indicate that, at least in part, the control of the synthesis of this RNA is at the level of gene transcription.

Base Sequence↗
PubMed1979

Cimetidine in the prevention of the pulmonary acid aspiration (Mendelson's) syndrome.

Cimetidine 200 mg was given i.v. 1 h before induction of anaesthesia to 20 patients about to undergo emergency surgery. There was an increase in pH of gastric aspirate in all patients (P less than 0.001) and in 80% pH was greater than 2.5 units at the time of induction of anaesthesia. The pH of gastric aspirate continued to increase after induction of anaesthesia and was greater than 4 units in all patients at the time of tracheal extubation and in the early recovery period.

Adolescent↗
PubMed1979

Quantitative analysis of specific labelled RNA'S using DNA covalently linked to diazobenzyloxymethyl-paper.

Substantial amounts of DNA (at least 25 microgram per cm2) can be stably bound to diazobenzyloxymethyl (DBM)-paper. Complementary RNA will hybridize to the DNA paper almost completely in 24 hours. Using several different conditions of hybridization and washing, the background of RNA bound non-specifically is very low (between 0.01 and 0.02%) and the efficiency of hybridization is very high (75 to 50% of complementary RNA is bound and retained through the washing procedure). Because the DNA is bound to the paper convalently, it is retained through all the washing and elution steps, and the DNA papers can be re-used many times.

Chromatography, Affinity↗
PubMed1979

Characterisation of bacterial clones containing DNA sequences derived from Xenopus laevis vitellogenin mRNA.

A 1700 nucleotide DNA sequence derived from Xenopus vitellogenin mRNA has been cloned in the bacterial plasmid pBR322. The identity of the cloned sequence was verified in two ways. Firstly, the plasmid DNA was shown to hybridise to an RNA of the correct size (6,700 nucleotides). This was shown by in situ hybridisation to electrophoretically separated RNA and also by the formation of "R-loops" with purified vitellogenin mRNA. Then, using a novel procedure in which plasmid DNA covalently bound to diazotised paper is used to select complementary mRNA sequences, the cloned sequence was shown to hybridise to an mRNA which directed the synthesis of vitellogenin when translated in a reticulocyte lysate cell-free system.

Animals↗