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Biomedical subjects

R Walker

Publications and source records attributed to R Walker.

At least 127 records · Page 7Linked to original sources
PubMed1998

Enterotoxigenic Clostridium perfringens type A necrotic enteritis in a foal.

A Thoroughbred-Quarter Horse crossbred foal developed hemorrhagic enteritis and died < 48 hours after birth. Gross and histologic findings were suggestive of Clostridium perfringens type C infection, and large numbers of C perfringens were isolated from intestinal contents. However, genotyping of isolates indicated that they were enterotoxigenic C perfringens type A, and isolates were found to produce C perfringens enterotoxin in vitro. This case suggests that enterotoxigenic C perfringens type A may cause enteric disease in horses.

Animals↗
PubMed1998

Hydrophobic forces dominate the thermodynamic characteristics of UvrA-DNA damage interactions.

The Escherichia coli DNA repair proteins UvrA, UvrB and UvrC work together to recognize and incise DNA damage during the process of nucleotide excision repair (NER). To gain an understanding of the damage recognition properties of UvrA, we have used fluorescence spectroscopy to study the thermodynamics of its interaction with a defined DNA substrate containing a benzo[a]pyrene diol epoxide (BPDE) adduct. Oligonucleotides containing a single site-specifically modified N2-guanine (+)-trans-, (-)-trans-, (+)-cis-, or (-)-cis-BPDE adducts were ligated into 50-base-pair DNA fragments. All four stereoisomers of DNA-BPDE adducts show an excitation maximum at 350 nm and an emission maximum around 380 to 385 nm. Binding of UvrA to the BPDE-DNA adducts results in a five to sevenfold fluorescence enhancement. Titration of the BPDE-adducted DNA with UvrA was used to generate binding isotherms. The equilibrium dissociation constants for UvrA binding to (+)-trans-, (-)-trans-, (+)-cis-, and (-)-cis- BPDE adduct were: 7.4+/-1.9, 15. 8+/-5.4, 11.3+/-2.7 and 22.4+/-2.0 nM, respectively. There was a large negative change in heat capacity DeltaCpo,obs, (-3.3 kcal mol-1 K-1) accompanied by a relatively unchanged DeltaGoobs with temperature. Furthermore, varying the concentration of KCl showed that the number of ions released upon formation of UvrA-DNA complex is about 3.4, a relatively small value compared to the contact size of UvrA with the substrate. These data suggest that hydrophobic interactions are an important driving force for UvrA binding to BPDE-damaged DNA.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1998

Saccadic eye movement and working memory deficits following damage to human prefrontal cortex.

A patient with a lesion confined largely to the right inferior frontal gyrus was found to be impaired on tests of spatial working memory and executive functioning. By contrast, his pattern recognition was good. The patient's selective impairments are consistent with the view that prefrontal cortex contributes to processes involved in spatial working memory. The patient was also tested on a range of oculomotor paradigms, some of which required the temporary suppression of a saccadic response. He was unable to suppress making contra- or ipsilesional reflexive glances to peripheral stimuli on the "anti-saccade" paradigm, but his performance improved on delayed saccade, memory-guided saccade and fixation tasks. Although reflexive glances were observed under these conditions they occurred more frequently in response to contralesional stimuli than ipsilesional ones. Furthermore, the patient had no difficulty in performing anti-point movements with his ipsilesional hand. Thus, his inability to suppress reflexive glances on the anti-saccade task is not due to a generalised problem of "distractibility". The patient's deficits are discussed in terms of models of anti-saccade generation and are related to recent findings regarding the role of prefrontal cortex in working memory and visual attention.

Attention↗
PubMed1998

Effect of baking and freeze-drying on the direct and indirect mutagenicity of extracts from the edible mushroom Agaricus bisporus.

The objectives of the study were to evaluate the effect of baking and freeze-drying on the direct and indirect mutagenicity in the Ames test of ethanolic extracts from the edible mushroom Agaricus bisporus. Direct mutagenicity was not influenced by baking for 10 min at 225 degrees C, but more prolonged baking, for example 4 hr at 100 degrees C reduced mutagenicity. Hepatic cytosol from Aroclor 1254-induced rats and mushroom tyrosinase potentiated the mutagenic response elicited by the mushroom extracts. Baking did not influence either of these processes. Finally, freeze-drying influenced neither the direct nor the indirect mutagenicity of the mushroom extracts. It is concluded that mutagenic and premutagenic compounds present in mushroom are generally not heat labile.

Agaricus↗
PubMed1998

Contribution of caffeine and flavanols in the induction of hepatic Phase II activities by green tea.

Aqueous extracts of green tea, at concentrations of 2.5. 5.0 and 7.5%, were administered to rats as the sole drinking fluid for 4 weeks. Hepatic glutathione S-transferase (GST) activity, determined using 1-chloro-2,4-dinitrobenzene (CDNB) and 3,4-dichloronitrobenzene (DCNB) as substrates, and UDP-glucuronosyl transferase activity, determined using 2-aminophenol as substrate, were induced but the effect was not always dose dependent. At the two highest doses, hepatic catalase activity was inhibited. In a second study, animals were exposed for 4 weeks to aqueous extracts (2.5%, v/v) of green tea, black tea (which has a much lower content of flavanols compared with green tea) and decaffeinated black tea. Treatment with the black tea enhanced GST activity, whether monitored using CDNB or DCNB, and the glucuronidation of 2-aminophenol. Treatment with decaffeinated black tea failed to modulate any of these activities, whereas treatment with green tea only enhanced the glucuronidation of 2-aminophenol. Finally, at this concentration of tea extract administration, black and decaffeinated black tea, but not green tea, suppressed catalase activity. It is concluded that neither flavanols nor caffeine are responsible for the induction of hepatic Phase II activities and inhibition of catalase activity in the rat.

Aminophenols↗
PubMed1998

Long-term cardiac arrest survivors of the Vienna emergency medical service.

The purpose of this study was to describe the life of survivors after successful resuscitation and to see if there was an association with the type of emergency cardiac care. The 'Utstein-style' data of patients surviving non-traumatic cardiac arrest 24 (14-32) months were prospectively collected. The everyday activities and psychological concerns of patients with a cerebral performance category (CPC) of 1 and 2 using a questionnaire were analyzed. The chi2-square test was used for statistical analysis. The questionnaires of 92 patients (median age 59, IQR 51-68; females 36) were evaluated. Patients enjoy life (84%; n=73), have depression (36%; n=31), consider their survival a 'second chance' (84%; n=73) and fear that they may suffer cardiac arrest again (56%; n = 45). The average quality of life is 7 on a scale from 0 (worst) to 10 (perfect). The majority of cardiac arrest survivors have a satisfactory life. No significant correlation between the type of emergency cardiac care and post cardiac arrest life was found. The fact that there was no association with the type of emergency cardiac care may be due to the narrow selection of patients (CPC 1 and 2), the small number of patients or factors contributing to post cardiac arrest life other than emergency treatment.

Activities of Daily Living↗
PubMed1998

Bacillus isolates from the spermosphere of peas and dwarf French beans with antifungal activity against Botrytis cinerea and Pythium species.

A range of isolation procedures including washing, sonication and incubation in nutrient broth were used separately and in combination to obtain potential bacterial antagonists to Botrytis cinerea and Pythium mamillatum from the testae and cotyledons of peas and dwarf French beans. Heat treatment was also used to bias this selection towards spore-forming bacteria. Ninety-two bacterial isolates were obtained, 72 of which were provisionally characterized as species of Bacillus. Four of these Bacillus isolates (B3, C1, D4 and J7) displayed distinct antagonism in vitro against Botrytis cinerea and P. mamillatum when screened using dual culture analysis. Further characterization of these antagonists using API 50CHB biochemical profiling identified isolate D4 as Bacillus polymyxa and isolates B3, C1 and J7 as strains of B. subtilis. In vitro screening techniques, using cell-free and heat-killed extracts of liquid cultures against Botrytis cinerea, demonstrated the production of antifungal compounds by these four Bacillus antagonists. With each isolate the antifungal activity was found not to be either exclusively spore-bound nor released entirely into the medium but present in both fractions. The antifungal compounds produced by these isolates were shown to be heat-stable. Their identification, production and release require further study for exploitation as biocontrol systems.

Antibiosis↗
PubMed1998

Collaborative relationships in general practice projects.

This article reports on a national study of collaborative relationships between general practitioners and other health care providers in 20 Division of General Practice projects. It argues that health care organisations will need to collaborate with others in the future and that much can be learnt from the literature on collaborative networks in business and community organisations. Successful collaborations between general practitioners and others were found to be consistent with a model of collaboration in 'under-organised domains', where pre-existing links between organisations are weak. Lessons are identified from the study to assist future collaborative ventures involving general practitioners.

Australia↗
PubMed1998

Toxicity testing and derivation of the ADI.

The ADI is an estimate of the amount of a chemical that can be ingested daily over a lifetime without appreciable health risk. It is derived from No-Observed-Adverse-Effect-Levels (NOAELs) determined in a battery of toxicity tests in animals and augmented by human data where available. The toxicity tests are intended (with a few exceptions) to embrace all the circumstances of human exposure to dietary chemicals. Hence these tests include chronic studies, sometimes with prior exposure in utero, and reproduction tests covering the reproductive phase including effects on the parental animals and the offspring. The tests should also cover the rapid growth phase from weaning to maturing. The ADI is calculated from the lowest NOAEL in the most sensitive test and the most sensitive species, unless other data indicate otherwise, and if the reproductive, neonatal or rapid growth phases indicate particular periods of sensitivity this should drive the numerical derivation of the ADI. In calculating the ADI, the NOAEL is divided by appropriate arbitrary or data-derived safety or uncertainty factors. Care in selecting the pivotal test, the NOAEL and the safety factors should ensure that the ADI does apply to children (or other age groups). However, because of the higher food intake of children on a body weight basis, specific risk management measures may be needed to ensure that the ADI is not exceeded.

Animals↗
PubMed1998

Adenovirus induction of an interferon-regulatory factor during entry into the late phase of infection.

Virus infection of animal cells can induce intracellular antiviral responses mediated by the induction of interferon-regulatory transcription factors (IRFs), which bind to and control genes directed by the interferon-stimulated response element (ISRE). The purpose of this study was to determine whether adenovirus (Ad) induces IRFs during infection, because they might play a role in promoting viral pathogenesis. Here we show that after the late phase of infection, Ad induces a transcription factor related to the IRF family of factors. The IRF is induced shortly after Ad entry into late phase and is shown to stimulate ISRE-directed transcription, to require activation by protein tyrosine kinase signalling, and to be induced several hours prior to the inhibition of cell protein synthesis. Inhibition of tyrosine kinase activity blocks Ad induction and activation of the IRF. Attempts to identify the Ad-induced factor immunologically and by photo-UV cross-linking indicate that it is likely a novel member of the IRF family. Finally, several independent lines of evidence also suggest that Ad induction of the IRF might correlate with the ability of the virus to block host cell protein synthesis later during infection.

Adenoviridae↗
PubMed1998

Acute barium intoxication following ingestion of ceramic glaze.

A case of deliberate overdose of barium sulphide in a psychiatric setting is presented, with resulting flaccid paralysis, malignant arrhythmia, respiratory arrest and severe hypokalaemia, but ultimately with complete recovery. The degree of paralysis appears to be related directly to serum barium levels. The value of early haemodialysis, particularly with respiratory paralysis and hypokalaemia, is emphasised.

Adult↗
PubMed1998

Acute bone pain following renal transplantation: differentiation between benign bone edema and avascular necrosis.

Two patients are reported who presented within the first 3 months posttransplantation with acute bone pain where serial magnetic resonance imaging (MRI) allowed differentiation between bone edema, which resolved spontaneously, and avascular necrosis (AVN) requiring core decompression. Case 1 had ill-defined images consistent with bone edema that resolved, whereas case 2 developed well-demarcated lesions in the femoral condyles and tibial epiphyses which were confirmed as AVN at surgery. Alternative explanations for bone edema were not evident. We would suggest that in any transplant recipient who develops acute bone pain, MRI is the initial diagnostic modality of choice. Evidence of development of well-demarcated lesions on serial MR scans indicate early AVN. However, on current evidence it is difficult to predict which lesions will progress and until greater experience becomes available, we would recommend intraosseous plethysmography and venography so that incipient or early AVN can be treated by core decompression of the affected bone.

Acute Disease↗
PubMed1998

Henoch-Schonlein purpura: the Chandigarh experience.

OBJECTIVE: To determine the clinical profile of children with Henoch-Schonlein purpura (HSP). DESIGN: Hospital based descriptive follow-up study. SUBJECTS: 45 patients attending the Pediatric Rheumatology and Immunology clinic over the last 4 years. RESULTS: The patients were aged between 2.5-12 years with a male to female ratio of 2:1. All cases had palpable purpura. Gastrointestinal involvement was seen in 38 patients, with abdominal pain in 35 (78%) and lower GI bleed in 21 (47%). Large joint arthritis occurred in 60%. Renal involvement was seen in 14 subjects (31%). Major renal involvement occurred in 9 patients, with nephritic syndrome in 6 and nephrotic syndrome in 3 cases. Five patients had minor urinary abnormalities; 6 patients with major renal involvement and crescentic glomerulonephritis were treated with high dose pulse steroid therapy followed by oral prednisolone and azathioprine for 12-18 months. Normalization of urinary abnormalities occurred in these patients over 4-8 months and presently all are normotensive and off antihypertensive drugs. CONCLUSIONS: HSP in children is a common form of vasculitis. Though short term results in HSP nephritis have been good, long term prognosis in those with major renal involvement would remain guarded.

Adolescent↗