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Biomedical subjects

A Clark

Publications and source records attributed to A Clark.

At least 181 records · Page 10Linked to original sources
PubMed1992

Analysis of lateral diffusion from a spherical cell surface to a tubular projection.

Cell surfaces are often heterogeneous with respect to the lateral distribution and mobility of membrane components. Because lateral mobility is related to membrane structure, measurement of a particular component's local diffusion coefficient within a distinct surface region provides useful information about the formation and maintenance of that region. Many structurally interesting cell surface features can be described as narrow tubular projections from the body of the cell. In a companion paper, we consider the thin "tethers" that can be mechanically drawn from the red blood cell membrane, and we measure the transport of fluorescent integral proteins from the surface of the cell body onto the tether. In this paper we present an analysis to describe the surface diffusion of membrane particles from a spherical shell onto a thin cylindrical process. Provision is made for different rates of diffusion within the two morphologically distinct regions. The relative role of each region in controlling the diffusive flux between regions is determined primarily by a single dimensionless parameter. This parameter incorporates the ratio of the two diffusion coefficients as well as the dimensions of each region. The analysis can be applied to a fluorescence photobleaching experiment in which the extended process is bleached. If the dimensions of the spherical cell body and the cylindrical extension are known, then the diffusion coefficients of both regions can be determined from the experimental fluorescence recovery curve.

Cell Membrane↗
PubMed1992

The Human Communication Research Centre dialogue database.

The HCRC dialogue database consists of over 700 transcribed and coded dialogues from pairs of speakers aged from seven to fourteen. The speakers are recorded while tackling co-operative problem-solving tasks and the same pairs of speakers are recorded over two years tackling 10 different versions of our two tasks. In addition there are over 200 dialogues recorded between pairs of undergraduate speakers engaged on versions of the same tasks. Access to the database, and to its accompanying custom-built search software, is available electronically over the JANET system by contacting liz@psy.glasgow.ac.uk, from whom further information about the database and a user's guide to the database can be obtained.

Adolescent↗
PubMed1992

A thermal clearance probe for continuous monitoring of cerebral blood flow.

Thermal clearance has been used as a measure of tissue blood flow for over 60 years. We have developed a probe which can be used to monitor cerebral cortical thermal clearance in patients suffering from acute neurosurgical disorders. Despite its limitations of size, invasiveness, small sample volume, and difficult quantification it has proved a reliable method, showing a good correlation between measured thermal clearance and the onset of clinical signs of ischaemia.

Adult↗
PubMed1992

Multicenter evaluation of the AntigEnz Chlamydia enzyme immunoassay for diagnosis of Chlamydia trachomatis genital infection.

To evaluate the AntigEnz Chlamydia enzyme immunoassay (EIA) (Baxter/Bartels, Issaquah, Wash.), we studied 320 men and 1,209 women attending clinics for sexually transmitted diseases in Baltimore, San Francisco, and Seattle. At examination, two separate swabs were obtained from each patient, one for chlamydial culture and one for EIA. Cervical samples were collected from women, and urethral samples were collected from men. The prevalence of chlamydial infection by culture was 9% in Baltimore (n = 532), 11% in Seattle (n = 500), and 9% in San Francisco (n = 497). To resolve specimens with discrepant culture and EIA results, the EIA transport buffer was centrifuged and the resuspended pellet was stained by direct immunofluorescence to determine whether elementary bodies were present. Overall sensitivity of the AntigEnz Chlamydia assay compared with culture was 87% in men and 86% in women, and overall specificities were 94 and 97%, respectively. Differences between centers were seen, with sensitivities ranging from 76% among men and 79% among women in Seattle to 100% among men and 95% among women in Baltimore. With a true positive considered to be either a culture-positive or an EIA- and direct immunofluorescence-positive specimen, the revised sensitivity was 91% in men and 88% in women. Overall revised specificity was 99% in both men and women. We conclude that in this high-prevalence population, the sensitivity and specificity of this assay compare favorably with those of other noncultural antigen detection tests for the diagnosis of chlamydial genital infection.

Antigens, Bacterial↗
PubMed1992

Antibodies to Saccharomyces cerevisiae in patients with Crohn's disease and their possible pathogenic importance.

Saccharomyces cerevisiae (baker's yeast) may play an important part in the pathogenesis of Crohn's disease. Because of this the levels of IgG and IgA antibodies against three S cerevisiae strains (NCYC 77, NCYC 79, and NCYC 1108) were assayed in 49 patients with Crohn's disease, 43 with ulcerative colitis, 14 with coeliac disease, and 21 healthy controls. Coded serum samples were tested by ELISA. Similar antibody patterns to all three strains were found. IgG and IgA antibody levels were significantly raised in patients with Crohn's disease compared with healthy controls (p < 0.001 and p < 0.0001 respectively) and with ulcerative colitis patients (p < 0.0001 and p < 0.0006 respectively). Raised IgA, but not IgG, yeast antibody levels were found in two patients with Crohn's disease who were intolerant to yeast, but these values were similar to those in other patients without yeast intolerance. In ulcerative colitis, both IgG and IgA levels were similar to normal controls. Patients with small bowel Crohn's disease had significantly higher IgG antibody levels than those with colonic disease (p < 0.01). High levels of IgG, but not IgA, antibody were present in patients with coeliac disease, the antibody responses being indistinguishable from those found in Crohn's disease. It is concluded that the presence of IgG antibody to S cerevisiae is characteristic but not specific to Crohn's disease. Although raised IgA antibody levels are more frequently found in Crohn's disease, their pathogenic importance remains to be established.

Adult↗
PubMed1992

Normal and elevated 3 alpha-androstanediol glucuronide concentrations in women with various causes of hirsutism and its correlation with degree of hirsutism and androgen levels.

We investigated peripheral androgen metabolic activity in 54 hirsute females (HF) by evaluating the serum 3 alpha-androstanediol glucuronide (3AG) concentration, hirsutism score (HS), and etiology of hirsutism. Based on basal and ACTH-stimulated steroid profiles (1 h post-Cortrosyn, 0.25 mg, i.v. bolus), the causes of hirsutism were determined to be increased adrenal androgen production (greater than 2 SD above normal mean), increased ovarian testosterone (T) production (greater than 2 SD above normal mean basal T of ovarian source only), or idiopathic cause (normal steroid profile). Serum 3AG levels in each group of HF were significantly higher (P less than 0.01-0.001) than those in normal females [normal: 2.9 +/- 0.94 nmol/L (n = 28); HF: increased adrenal androgen production of undefined cause, 7.7 +/- 7.5 nmol/L (n = 14); 21-hydroxylase deficiency, 7.6 +/- 7.4 nmol/L (n = 5); increased ovarian T production 5.5 +/- 3.5 nmol/L (n = 18); idiopathic cause, 5.8 +/- 4.8 nmol/L (n = 17)]. However, normal 3AG levels (less than 5.2 nmol/L) were present in 50-67% of HF in each group. Collectively, 3AG levels in HF correlated significantly (P less than 0.01) with dehydroepiandrosterone (DHEA; r = 0.41) and DHEA sulfate (DS; r = 0.44), while the correlation with androstenedione (r = 0.15) or T (r = 0.19) was not significant. Serum 3AG and adrenal androgen levels decreased in all subjects after dexamethasone treatment (0.5-1 mg at hour of sleep; 2 mg/day for 3-5 days). The correlation between 3AG and HS was significant (r = 0.6-0.74; P less than 0.01-0.001) only in HF with increased adrenal androgen secretion and idiopathic cause, and was not significant (r = 0.42) in HF with increased ovarian T secretion. There was no significant correlation between androgen levels and HS. We conclude that the serum 3AG level was not consistently elevated in HF and did not differ significantly between the various causes. Significant correlations between 3AG and DHEA/DS levels, and the simultaneous decrease in 3AG and adrenal androgens after dexamethasone administration in HF suggest that adrenal androgens contribute significantly to 3AG production. The significant correlation between 3AG and HS in HF with increased adrenal androgen secretion and idiopathic cause indirectly suggests an adrenal androgen contribution to both 3AG production and hirsutism in these HF. The insignificant correlation between 3AG and HS in HF with increased ovarian T secretion may result from a confounding effect of ovarian T on hirsutism.

Adolescent↗
PubMed1992

Fetus with unbalanced translocation involving chromosomes 2 and 11.

We report a fetus with an unbalanced translocation between chromosomes 2 and 11, the product of a paternal balanced reciprocal translocation, fetal karyotype 46, XX, -11, +der(11)t(2;11) (q35;q24.1)pat. The fetus had unusual facial features. The relevance of this case to mapping of the type I Waardenburg syndrome gene is discussed.

Abnormalities, Multiple↗
PubMed1991

Change in obstetric practice in response to fear of litigation in the British Isles.

The increased number of medical negligence claims against obstetricians and gynaecologists has led to concerns about a trend towards defensive medical practice in the UK. The attitudes of obstetricians in the British Isles to tests of fetal and maternal wellbeing, which may influence decisions about patient care, were investigated in 3194 Fellows and Members of the Royal College of Obstetricians and Gynaecologists. Perceived accuracy of tests ranged from 86.3% for fetal blood sampling to 25.9% for biochemical tests. Despite some tests being perceived as having poor accuracy, all were widely used even by those who deemed them inaccurate. The most frequent explanations given for this paradoxical finding were that such tests were an aid to clinical judgement and were necessary for medicolegal reasons. Our data indicate that tests deemed to be inaccurate are used in clinical practice because some obstetricians fear litigation. Our findings were not influenced by age, gender, grade of doctor, or site of practice.

Attitude of Health Personnel↗
PubMed1991

Oxoaporphine alkaloids: conversion of lysicamine into liriodendronine and its 2-O-methyl ether, and antifungal activity.

Pschorr reaction of diazonium salt 7 in aqueous methanolic sulfuric acid afforded, besides lysicamine 2, the orange colored sulfate of oxodibenzopyrrocoline (8). The structure is fully supported by an X-ray analysis of its picrate salt. Selective ether cleavage of lysicamine (2) with 48% HBr afforded a hydrobromide of 9, and free betaine 9 on treatment with pyridine-water. Both compounds methylated on treatment with etherial diazomethane on nitrogen to give the known 2-O,N-dimethylliriodendronine (11). Liriodendronine (10) was obtained from lysicamine (2) on heating with pyridine HBr at 189 degrees C, and treatment with pyridine-water, as a dark violet betaine. Betaine 12 was obtained by heating 11.HCl to 200 degrees C. The quaternary salts of lysicamine, lysicamine methiodide (3) and lysicamine methosulfate (4) were comparable in anticandidal activity to liriodenine (1), but were not as active as liriodenine methiodide (13).

Alkaloids↗
PubMed1991

Localisation of islet amyloid polypeptide and its carboxy terminal flanking peptide in islets of diabetic man and monkey.

Islet amyloid polypeptide is a normal constituent of islet Beta cells and is derived from a larger precursor by removal of flanking peptides at the carboxy (C) and amino (N) terminals. The role of these flanking peptides in the formation of amyloid in Type 2 (non-insulin-dependent) diabetes mellitus and in insulinomas is unknown. The C-terminal flanking peptide of islet amyloid polypeptide was localised by immunocytochemistry in human and monkey pancreatic islets from Type 2 diabetic and non-diabetic individuals by use of specific polyclonal antisera. Immunoreactivity for the C-terminal peptide was found in insulin-containing cells in both diabetic and non-diabetic tissue: no antibody binding was detected in islet amyloid of Type 2 diabetic man or of monkeys although a positive reaction occurred with antisera for islet amyloid polypeptide. The C-terminal peptide was localised by immunogold electron microscopy in the insulin granules in both diabetic and non-diabetic individuals but, unlike islet amyloid polypeptide, was not detected in lysosomes. The absence of immunoreactivity for the C-terminal peptide in amyloid suggests that incomplete cleavage of this flanking peptide from islet amyloid polypeptide is not a factor in the formation of islet amyloid.

Adult↗
PubMed1991

Non-linkage of the islet amyloid polypeptide gene with type 2 (non-insulin-dependent) diabetes mellitus.

Type 2 (non-insulin-dependent) diabetes is associated with the deposition of islet amyloid. The major formative peptide, islet amyloid polypeptide, has recently been characterised and an abnormality of the structure or expression of this gene is a possible candidate for the inherited component of Type 2 diabetes. A restriction fragment length polymorphism of the gene has been identified with Pvu II. To study the relationship between the islet amyloid polypeptide gene and Type 2 diabetes, two distinct genetic approaches have been undertaken. Firstly, non-linkage has been demonstrated in four pedigrees, with four normoglycaemic first degree relatives having an allele associated with diabetes in other family members, and one affected relative not having the putatively associated allele. The LOD score taking age-related penetrance into account was -1.68, making linkage unlikely (p = 0.02). Secondly, in a population-based restriction fragment length polymorphism survey, no linkage disequilibrium of the alleles was found between a population of unrelated Caucasian subjects with Type 2 diabetes and a normal population. A mutation in or near the islet amyloid polypeptide gene is thus unlikely to be a common cause of Type 2 diabetes.

Amyloid↗
PubMed1991

Astemizole-induced ventricular arrhythmias: an unexpected cause of convulsions.

Antihistamines are commonly used drugs. The more recent additions to the formulary are less sedative, but have been implicated as a cause of ventricular arrhythmias. We report a case in which a deliberate overdose of astemizole was associated with Mobitz type two heart block and prolongation of the QT interval, causing the so-called torsade-de-pointes ventricular tachycardia.

Adolescent↗
PubMed1991

Introducing information in dialogues: forms of introduction chosen by young speakers and the responses elicited from young listeners.

Young speakers in dialogue must establish mutual knowledge. Traditionally, researchers have focused on how children used indefinite and definite articles to signal novel and shared information. In this study of 170 children aged seven to thirteen, the form of introduction chosen, whether question or statement, is more significant than the type of article used. No developmental effects on article use emerge, with statement + indefinite always the least common choice. However, young speakers use question introductions significantly less than older children. There is also a developmental interaction between speakers' and listeners' behaviour. Question introduction elicit effective listener responses at all ages, but only twelve-year-olds respond reliably to statements. Unfortunately, young speakers prefer just those forms of introduction to which young listeners are least likely to provide informative feedback. Thus two separate developmental effects appear to combine to hamper young subjects' chances of achieving successful communication in dialogues.

Age Factors↗