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Biomedical subjects

A Thomas

Publications and source records attributed to A Thomas.

At least 343 records · Page 19Linked to original sources
PubMed1994

The reactivity of chloramphenicol reduction products with DNA bases.

PURPOSE: The interaction between the constituent bases of deoxyribonucleic acid and the reduction products of the nitro-aromatic compound chloramphenicol and its nitroso derivative have been studied using an electrochemical system. METHODS AND MATERIALS: The changes to the voltammetry of chloramphenicol and nitrosochloramphenicol upon addition of adenine, cytosine, guanine, and thymine at various concentrations have been measured. The biological implications of reductive activation of both chloramphenicol and nitrosochloramphenicol were examined using a phi X174 double transfection technique which measures biologically relevant deoxyribonucleic acid damage. RESULTS: Measurement of the voltammetric response of chloramphenicol shows that the most noticeable change upon base addition is a decrease in the lifetime of the nitro radical anion in the following order of decreasing activity: adenine, thymine, and cytosine. No effect was observed with guanine. The reversible 2-electron nitrosochloramphenicol-hydroxychloramphenicol couple showed no interaction on the voltammetric timescale, although binding of the hydroxylamine to guanine was observed. Interaction of the azo derivative, formed as a consequence of further reduction plus chemical reaction of nitrosochloramphenicol was observed. Biological studies showed that no significant effect on deoxyribonucleic acid by chloramphenicol or nitrosochloramphenicol was observed under oxic conditions. Controlled reduction of nitrosochloramphenicol to the hydroxylamine gave considerably less damage than when nitrosochloramphenicol or chloramphenicol was completely reduced. CONCLUSION: The chloramphenicol nitro radical anion reacts selectively with the bases of deoxyribonucleic acid. Reduction products of nitrosochloramphenicol beyond the 2-electron hydroxylamine are highly reactive to deoxyribonucleic acid.

Chloramphenicol↗
PubMed1994

Familiality of cancer in Utah.

The Utah Population Database allows examination of the genetic relationships among the 35.7% of all cancer cases in the state that have genealogical records. Familial clustering of cancer is measured by the Genealogical Index of Familiality and is examined by site, and within site by age of onset, histology, and gender. Most cancer sites examined show excess familiality for all cases considered together. Subsets of individuals with certain characteristics showed unusually high levels of familial clustering, specifically lymphocytic leukemias and especially chronic lymphocytic leukemia, lobular breast cancer, early lip cancer, early melanoma, and female lung cancers of alveolar/adenoma histology. These may represent characteristics of the most penetrant forms of inherited susceptibilities, those which are enhanced by environmental factors, chance aggregations, rare inherited syndromes, or a combination of these factors.

Age Factors↗
PubMed1994

Ability of human sera to neutralise the activity of Vero cytotoxins VT1, VT2 and variant forms of VT2.

Sera, from 17 patients with diarrhoea or haemolytic uraemic syndrome, and six healthy adults, were tested for neutralisation of Vero cytotoxins (VT). For all 17 patients there was evidence of infection with Escherichia coli O157. Sera from two controls but from none of the patients neutralised VT1, although two patients were infected by strains producing VT1 and VT2. Sera from all six controls and 14 patients neutralised VT2 derived from strains 933 and E32511, but not variant forms of VT2 derived from strains E32511, E57, B2F1 and H.1.8. This neutralising activity warrants further investigation, especially as many O157 VTEC carry both VT2 and VT2 variant genes.

Adolescent↗
PubMed1994

Rhesus monkey behavior during exposure to high-peak-power 5.62-GHz microwave pulses.

Limits on the exposure to high-peak-power, short-duration microwave pulses have only recently been adopted. Additional data, however, are needed to understand the effects that may be produced by exposure to high-peak-power pulsed microwaves. Four male rhesus monkeys (Macaca mulatta) were trained on an operant task for food pellet reward to investigate the behavioral effects of very high-peak-power 5.62 GHz microwaves. The operant task required monkeys to pull one plastic lever on a variable interval schedule (VI-25 s) and then respond to color signals and pull a second lever to obtain food. The monkeys were conditioned to perform a color discrimination task using one of three colors displayed by a fiber-optic cable. A red signal was the discriminative stimulus for responding on the first lever. A response on the second lever when a green signal was presented (1 s duration) delivered a food pellet. If a response on the second lever was made in the presence of a white signal, a 30-s timeout occurred. While performing the behavioral task, the monkeys were exposed to microwave pulses produced by either a military radar (FPS-26A) operating at 5.62 GHz or the same radar coupled to a Stanford linear energy doubler (SLED) pulse-forming device (ITT-2972) that enhanced peak power by a factor of nine by adding a high power pulse to the radar pulse. The effects of both types of pulses were compared to sham exposure. Peak field power densities tested were 518, 1270, and 2520 W/cm2 for SLED pulses and 56, 128, and 277 W/cm2 for the radar pulses. The microwave pulses (radar or SLED) were delivered at 100 pps (2.8 microseconds radar pulse duration; approximately 50 ns SLED pulse duration) for 20 min and produced averaged whole-body SARs of 2, 4, or 6 W/kg. Compared to sham exposures, significant alterations of lever responding, reaction time, and earned food pellets occurred during microwave exposure at 4 and 6 W/kg but not at 2 W/kg. There were no differences between radar or SLED pulses in producing behavioral effects.

Analysis of Variance↗
PubMed1994

A linear time algorithm for calculation of multiple pairwise kinship coefficients and the genetic index of familiality.

We present an algorithm that calculates the mean kinship coefficient between all pairs of individuals in a given set relative to a known pedigree. The time required to make the calculations is proportional to the size of the set. The constant of proportionality is determined by the number of generations that the pedigree spans. A simple alteration to the algorithm allows efficient calculation of all pairwise kinship coefficients within a set of individuals.

Algorithms↗
PubMed1994

Isolation of Vero cytotoxin-producing Escherichia coli serotypes O9ab:H- and O101:H-carrying VT2 variant gene sequences from a patient with haemolytic uraemic syndrome.

Vero cytotoxin-producing Escherichia coli (VTEC) were isolated from the faecal specimen of a patient with haemolytic uraemic syndrome. The isolates belonged to two rare VTEC serotypes, O9ab:H- and O101:H-. Polymerase chain reaction gene amplification products were detected with primers specific for the VT2e gene, a variant of VT2. The toxin from both isolates was cytotoxic to Vero cells but not to HeLa cells. An 18 kb EcoRI restriction enzyme fragment of genomic DNA from both strains hybridised with a VT2 polynucleotide DNA probe.

Aged↗
PubMed1994

Stored skin--stored trouble?

Quantitative bacteriology is presented on 102 consecutive split-skin grafts. A sample of graft was cultured whenever skin was taken and whenever stored skin was used. Stored skin unused at 21 days was also cultured. The percentage take of grafts was inversely proportional to number of organisms/g of skin (r = -0.24, p < 0.05). Commonly used storage conditions facilitated bacterial multiplication. There was no significant difference in organisms/g contaminating grafts for different surgeons, skin preparations, types of grafts, cutting tools or mode of anaesthesia. Male patients had a significantly greater count for initial grafts (p = 0.02), but after 3 weeks storage there was no sex difference.

Adolescent↗
PubMed1994

Spiritual and religious beliefs in acute illness--is this a feasible area for study?

In this paper we discuss the measurement of spiritual, religious and philosophical beliefs in patients admitted to hospital with acute physical illness. The discussion is based on the results of a preliminary study of the beliefs of 300 patients studied by face-to-face interview and questionnaire. Principal outcome measures at 6 months were self reported psychological and belief scores and physical state as reported in the medical records. Two thirds of patients reported a religious and/or spiritual belief system. Strength of belief was not associated with social, psychological or diagnostic factors. However, those patients with a religious and/or spiritual life view who expressed strong beliefs were likely to fare less well clinically. We conclude that empirical study of patients' beliefs is possible, though care must be exercised over the measures used. Beliefs were at least as predictive of outcome as other social and psychological factors. This area is of considerable importance to patients and should not be neglected by carers or researchers.

Acute Disease↗
PubMed1994

Modified resectoscope loop for transurethral resection of the ejaculatory duct.

We report the design of a modified resectoscope loop for transurethral resection of the ejaculatory ducts. The loop is a modification of a standard 24 F resectoscope loop. Cutting dimensions are 2.5 mm in width and 3 mm in depth for the modified loop versus 6 mm in width and 5 mm in depth for the conventional loop. This modification allows precise resection of obstructed ejaculatory ducts with minimal trauma to the prostatic fossa, reducing the potential for troublesome bleeding.

Ejaculatory Ducts↗
PubMed1994

Genetic models for the inheritance of the silver colour mutation of foxes.

We consider genetic models for the inheritance of the particular colour patterns of silver foxes. The models are evaluated by computation of statistical likelihoods based on observations of related foxes in extended pedigrees. Problems caused by incomplete paternity information are addressed by inferences based on phenotypic observations. The unreliability of subjective evaluations of fur colour also provides difficulty, in particular crossfoxes emerge as being difficult to differentiate. No evidence of linkage between Agouti locus and Extension locus is found in this dataset.

Alleles↗
PubMed1994

Genomic mismatch scanning in pedigrees.

The new method of genomic mismatch scanning allows the high-resolution mapping of identity by descent on the chromosomes of two related individuals. Modelling recombinant events as a continuous Markov process, the authors design experiments and statistical tests for the use of this technique on sets of affected individuals in pedigrees in order to determine candidate regions for genes contributing to the disease.

Animals↗
PubMed1994

Linkage analysis on complex pedigrees by simulation.

A Markovian scheme for simulating the genotypes of individuals in a pedigree subject to constraints imposed by observed phenotypes is used to estimate the logarithm of a likelihood ratio in linkage analysis. The method is illustrated on a fictitious pedigree by comparison with exactly calculated results.

Animals↗
PubMed1994

A probabilistic model for detecting coding regions in DNA sequences.

A probabilistic model is presented to predict whether or not an anonymous sequence of DNA contains exons. The method is shown to be at least as reliable as Grail, a well-known neural network solution to the problem, and to be significantly more amenable to customization for specific prediction problems.

Base Sequence↗