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Biomedical subjects

D A Walker

Publications and source records attributed to D A Walker.

At least 19 recordsLinked to original sources
PubMed1992

Comparison of polymerase chain reaction amplification of two mycobacterial DNA sequences, IS6110 and the 65kDa antigen gene, in the diagnosis of tuberculosis.

BACKGROUND: Knowledge of the sequences of mycobacterial genes and the availability of DNA amplification techniques have raised the possibility that identification of mycobacterial DNA may offer a rapid and specific diagnostic test for tuberculosis. The correlation between the presence of Mycobacterium tuberculosis DNA and clinical tuberculosis, however, is not known. This study compared the results of polymerase chain reaction amplification of two M tuberculosis DNA sequences, IS6110 and the gene encoding the 65kDa heat shock protein (65kDa Ag), from sputum, bronchoscopy washings, and bronchoalveolar lavage fluid and related these findings to the presence of active and past tuberculosis. METHODS: Highly specific primers were used for amplification of IS6110 and 65kDa Ag DNA. Analysis was performed on one or more samples from 87 patients. RESULTS: IS6110 DNA was identified in samples from all six patients with active tuberculosis, from 15 to 18 patients with past tuberculosis, from five of nine contacts of patients with tuberculosis, and from nine of 54 patients with lung disease unrelated to tuberculosis. The 65kDa Ag DNA was identified in samples from all patients with active and past tuberculosis, from contacts of patients with tuberculosis, and from 14 of 42 patients with non-tuberculous lung diseases. CONCLUSION: These data suggest that the presence of IS6110 DNA correlates more closely with a tuberculosis related diagnosis than that of 65kDa Ag DNA and that both DNAs are found in most subjects with past tuberculosis or contacts of patients with tuberculosis. This may limit the clinical usefulness of these tests.

Base Sequence↗
PubMed1989

Coregulation of electron transport and Benson-Calvin cycle activity in isolated spinach chloroplasts: studies on glycerate 3-phosphate reduction.

Glycerate 3-phosphate-dependent O2 evolution was measured in intact chloroplasts in the absence of CO2. At all concentrations of added glycerate 3-phosphate oxygen evolution ceased before stoichiometric amounts of oxygen were evolved. The inhibition of glycerate 3-phosphate-dependent-O2 evolution increased with increasing concentrations of substrate added. A similar response was observed in chloroplasts treated with KCN which inhibits ribulose-1,5-bisphosphate carboxylase-oxygenase. Oxygen uptake via the oxygenase activity of this enzyme is therefore not the cause of the discrepancy in stoichiometry of oxygen release in this system. The addition of NaHCO3 to chloroplasts in which oxygen evolution was inhibited by glycerate 3-phosphate caused an immediate sustained rate of oxygen evolution in the absence of KCN but not with KCN present. Simultaneous measurements of chlorophyll a fluorescence showed that qQ remained oxidized, although net O2 evolution had ceased. As O2 evolution decreased, qE and delta pH increased. Upon the addition of the NaHCO3, QA became more oxidized while delta pH and qE were decreased, suggesting that the inhibition of electron transport at high glycerate 3-phosphate concentrations was mediated by photosynthetic control via delta pH. However, the levels of ATP, ADP, ribulose 1,5-bisphosphate, and Pi concentrations and ATP/ADP ratio. The stromal glycerate 3-phosphate content declined upon illumination until O2 evolution ceased. At this time a constant stromal glycerate 3-phosphate concentration of 8-10 mM was maintained while net import of glycerate 3-phosphate into the stroma had virtually ceased. The stromal triosephosphate content remained at a constant low level throughout but the glycerate 3-phosphate level increased slightly after addition of NaHCO3. The data provided by the measurements of thylakoid reactions and stromal metabolites suggest that photosynthetic electron transport is tightly coupled to the requirements of the stroma for ATP and NADPH. Glycerate 3-phosphate reduction requires much less ATP than the operation of the complete Benson-Calvin cycle since the stoichiometry of ATP and NADPH utilization is reduced to 1:1. We conclude that thylakoid electron flow is not sufficiently flexible to maintain NADPH and ATP production in the ratio of 1:1. This situation will favor overenergization of the thylakoid membrane, increased leakiness of protons, increased electron drainage to O2, and result in progressive inhibition of noncyclic electron flow.

Antimycin A↗
PubMed1989

Enhanced cis-platinum ototoxicity in children with brain tumours who have received simultaneous or prior cranial irradiation.

We report on four children who received cis-platinum simultaneously with, or in one case 10 months after, cranial irradiation and experienced exaggerated ototoxicity affecting all audible frequencies. The hearing loss was severe, affecting the critical areas for speech perception, and necessitated the provision of bilateral hearing aids. The audiograms of these patients are shown and compared to those of four children who had received cis-platinum as part of their treatment for neuroblastoma but without cranial irradiation. The precipitation of the exaggerated hearing loss with the administration of cis-platinum in one patient 10 months after finishing cranial irradiation suggests that care should be taken in the timing of cis-platinum administration in relation to concurrent or previous cranial irradiation.

Adolescent↗
PubMed1988

Alterations in nasal respiration and nasal airway size following superior repositioning of the maxilla.

Twenty patients who underwent superior repositioning of the maxilla via Le Fort I down fracture had their respiratory mode and nasal cross-sectional area determined prior to and 6 months following surgery. Inductive plethysmography and nasal air flow techniques were used in the determination of these parameters. Prior to surgery, five patients were nasal breathers, five were predominantly nasal breathers, six were oral-nasal breathers, and four were predominantly oral breathers. Nine patients had inadequate nasal airways. Six months following surgery, 14 patients were nasal breathers and six were predominantly nasal breathers. Sixteen patients had adequate nasal airways, three had borderline nasal airways and one had an inadequate nasal airway postsurgically. These findings suggest that superior repositioning of the maxilla by Le Fort I down fracture does not adversely affect nasal respiration. Nasal function actually improved in 17 of the 20 subjects studied.

Adolescent↗
PubMed1987

Effect of lithium on the metabolic response to parathyroid hormone.

Blood and urine samples were collected at timed intervals for up to 120 min after the start of a 30-min infusion of 30 IU bovine parathyroid hormone (PTH) into 6 normal male subjects. Infusions were performed before and after 7 days' treatment with lithium carbonate. A highly significant increase in the maximum renal tubular reabsorption capacity for calcium (TmCa/GFR) from 2.02 +/- 0.04 to 2.17 +/- 0.07 mmol/l (p less than 0.02) produced a significant rise in plasma calcium. Lithium had no effect on basal fasting PTH or nephrogenous cyclic AMP (cAMP). Changes in nephrogenous cAMP and TmP/GFR in response to PTH were not altered by lithium. The absorption of 47Ca following an oral calcium load was increased in 5 out of 6 subjects also treated for 1 week with lithium. These results suggest that lithium has a direct effect on calcium transport, both at the level of the renal tubule and the gut, which is not mediated by stimulation of parathyroid activity or via modification of PTH-stimulated adenylate cyclase.

Adult↗
PubMed1985

Necrotizing granulomatous splenitis complicating leukemia in childhood.

Two children are described with acute leukemia in remission who both developed a swinging pyrexia and pathologically identical splenic necrotizing granulomata. No organisms were seen in, or isolated from, either spleen. After splenectomy, systemic symptoms persisted and did not resolve until steroids were given. The etiology of this syndrome remains unknown.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

The relationship between light scattering and chlorophyll a fluorescence during oscillations in photosynthetic carbon assimilation.

Light scattering, which can be taken as an indicator of the transthylakoid proton gradient, and the 518-nm rise, which can be regarded as a measure of the transthylakoid membrane potential, have been followed during oscillations in chlorophyll a fluorescence, which are known to be associated with corresponding changes in photosynthetic carbon assimilation. Both components oscillated in a manner which was broadly reciprocal to chlorophyll a fluorescence. However, there was a phase shift such that the light-scattering change usually anticipated fluorescence and often also the 518-nm shift. It is concluded that the proton motive force rises and falls slightly in advance of rises and falls in carbon assimilation. The relationship of these changes to a possible underlying mechanism is discussed.

Carbon↗
PubMed1985

The role of serum tumour markers to aid the selection of lung cancer patients for surgery and the assessment of prognosis.

We have measured the following ten serum proteins in a sample of 290 patients presenting with possible lung cancer: carcinoembryonic antigen (CEA), alpha 1-acid glycoprotein (AGP), C-reactive protein (CRP), ferritin (FER), prealbumin (PAB), third component of complement (C3), immunoglobin E (IgE), alpha 2-pregnancy-associated glycoprotein (PAG), beta 2-microglobulin (beta 2-m) and retinol binding protein (RBP). It is found that, with the exception of PAG, C3 and IgE, there are significant differences between protein concentrations in the subsequently diagnosed cancer and non-cancer patients. However, protein concentrations in the cancer patients who were suitable for surgery do not differ significantly from the concentrations in inoperable patients. The prognostic significance of the proteins in the inoperable and operable cancer patients is also envisaged. In the operable group C3 appears to be useful, whilst AGP and RBP are prognostic indicators in the inoperable group.

Blood Proteins↗
PubMed1984

Influence of glycerate on photosynthesis by wheat chloroplasts.

Glycerate was found to effect photosynthetic O2 evolution in wheat chloroplasts by its conversion to triose phosphate and by influencing the rate of photosynthesis through the reductive pentose phosphate pathway. In the absence of bicarbonate, the photosynthetic O2 evolution with glycerate was low (10 to 25 mumol mg chlorophyll-1 h-1), and only about 15% of the rate of bicarbonate-dependent O2 evolution under optimum conditions. This corresponds to a rate of glycerate conversion to triose phosphate of 20 to 50 mumol mg chlorophyll-1 h-1, which appears sufficient to accommodate flux through the glycolate pathway in vivo. Pi was required for this glycerate-dependent O2 evolution; rates remained relatively constant between 0.1 and 40 mM Pi, and proceeded with little lag upon illumination (less than 0.5 min). Evidence for O2 evolution due to glycerate conversion to triose phosphate could be conclusively demonstrated by addition of glycolaldehyde, an inhibitor of the regenerative phase of photosynthesis, which prevents CO2 fixation. The effect of glycerate on photosynthesis in the presence of bicarbonate was determined by measuring both photosynthetic O2 evolution and 14CO2 fixation at varying Pi concentrations. Low concentrations of glycerate (micro- to millimolar levels) prevented inhibition of photosynthesis by Pi. With 1 mM bicarbonate and pH 8.2, which is favorable for glycolate synthesis, maximum rates of photosynthesis were obtained at low Pi (25 microM), whereas strong inhibition of photosynthesis occurred at only 0.2 mM Pi. Addition of glycerate relieved the inhibition of photosynthesis by Pi, indicating the possible importance of glycerate metabolism in the chloroplast under photorespiratory conditions. The initiation of photosynthesis by glycerate at inhibitory Pi levels occurred with little reduction in the ratio of CO2 fixed/O2 evolved, and the main effect of glycerate was on carbon assimilation. While the basis for the beneficial effect of glycerate on CO2 assimilation under moderate to high Pi levels is uncertain, it may increase the concentration of 3-phosphoglycerate (PGA) in the chloroplast, and thus make conditions more favorable for induction of photosynthesis and reduction of PGA to triose phosphate.

Bicarbonates↗
PubMed1984

Haemophilia and T lymphocyte subsets.

Number of circulating lymphocytes and T cell subsets were assessed in 13 boys with severe haemophilia and 12 age matched controls. There was no significant difference between the two groups. This conflicts with previous findings in adults where lymphopenia and changes in T cell subpopulations have been found frequently.

Antibodies, Monoclonal↗