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Biomedical subjects

A Clark

Publications and source records attributed to A Clark.

At least 289 records · Page 16Linked to original sources
PubMed1983

Capture of spatially homogeneous chemical reactions in tissue by freezing.

A useful technique in studying the saturation of hemoglobin in erythrocytes or myoglobin in tissue is cryophotometry, in which tissue is frozen for later spectrophotometric analysis. A general question associated with this technique is whether the freezing process alters the chemical state. This paper presents a theoretical analysis of the simplest model relevant to that question. We study the effect of rapid cooling on a spatially homogeneous chemical reaction. The analysis shows that changes during freezing are negligible near the boundary to which the heat sink is applied, but can be significant deeper in the sample. The distance from the boundary at which the changes during freezing become appreciable can be expressed simply in terms of the chemical reaction rates and the thermal diffusivity of the tissue. Detailed results are given for the case of oxygen and myoglobin in skeletal muscle.

Animals↗
PubMed1983

A comparison of live and inactivated influenza A (H1N1) virus vaccines. 1. Short-term immunity.

Groups of volunteers were immunized subcutaneously with one of three inactivated influenza virus A/USSR/77 (H1N1) vaccine preparations; a whole virus vaccine, a surface-antigen subunit adsorbed vaccine, or an aqueous surface-antigen subunit vaccine. The reactions to immunization were recorded, and the antibody response was measured 1 month later. A fourth group of volunteers were inoculated intranasally with live attentuated A/USSR/77 (H1N1) influenza virus; the reactions and antibody response of these volunteers were also measured. One month after immunization, the incidence of infection by challenge with homologous live attentuated virus was determined for all groups of volunteers. The results showed that all four vaccines used were relatively non-reactogenic, and that inactivated vaccines induced higher titres of serum antibody than the live attenuated vaccine. All the vaccines induced significant protection against challenge virus infection which was directly related to the level of serum HI antibody response.

Adolescent↗
PubMed1983

A comparison of live and inactivated influenza A (H1N1) virus vaccines. 2. Long-term immunity.

Groups of volunteers were immunized with one of three influenza virus vaccines, and the resistance to challenge infection with attenuated influenza A (H1N1) virus was measured 8 months later. The vaccines were aqueous subunit influenza A/USSR/77 (H1N1) vaccine, aqueous subunit influenza B/Hong Kong/73 vaccine, or attenuated influenza virus A (H1N1) vaccine. The B virus vaccine was included as a control to assess the incidence of natural A virus infection during the study period. A proportion of the B virus vaccinees had pre-existing A (H1N1) virus antibody and were used to study the immunity conferred by natural infection to the live virus challenge. The serum antibody responses were measured at 1 and 8 months after immunization. The results showed that all the vaccines induced serum HI antibody in a proportion of the volunteers; however, after 1 month, higher titres of serum antibody were found in volunteers given inactivated A vaccine than in those given live attenuated A virus vaccine. Eight months post-immunization the titres of serum antibody in volunteers given inactivated vaccine had declined significantly, but there were no changes in the antibody titres of those given live virus vaccine. The incidence of infection by the challenge virus at 8 months post-immunization was directly related to the serum antibody titres 1 month post-immunization; no evidence was obtained to suggest that those given live virus vaccine had a more solid immunity than those given inactivated vaccine.

Adolescent↗
PubMed1983

A graded-dose study of inactivated, surface antigen influenza B vaccine in volunteers: reactogenicity, antibody response and protection to challenge virus infection.

One hundred and nineteen volunteers were divided into five groups, and each volunteer inoculated subcutaneously with an aqueous subunit B/Hong Kong/73 vaccine containing 40, 20, 10, or 5 micrograms of HA or saline alone in a 0.5 ml volume. The incidence of reactions was recorded 24 h after inoculation. One month following immunization the serum HI antibody to B/Hong Kong/73 virus was measured; each volunteer was inoculated intranasally with live, attenuated influenza B (RB77) virus; and the incidence of infection by the challenge virus was determined by HI antibody response. The results showed that the incidence of reactions to all doses of vaccine were relatively low, the severity mild, and the duration short. However, the incidence of reactions was highest for those given 40 micrograms HA and least for those given 5 micrograms HA. The serum HI antibody responses to vaccine showed a dose-response relationship. For volunteers given 40 micrograms HA, 22 (96%) showed a fourfold rise in antibody titre and all volunteers had antibody titres of greater than 40 following immunization: for volunteers given 5 micrograms HA the g.m.t. increased from 16.6 to 86.1; and for those given 10 and 20 micrograms HA the response was intermediate. Following challenge, the lowest incidence of infection was seen in volunteers given the highest dose of vaccine. However, all doses of vaccine induced some protection against challenge virus infection, and the incidence of infection was directly related to the serum antibody titre at the time of challenge. The 50% protection titre of serum HI antibody was estimated as 15 to 20.

Adolescent↗
PubMed1983

Factor structure and discriminant validity of the SCL-90 in a veteran psychiatric population.

This study tested whether the symptom dimension subscales derived for the Symptom Checklist-90 (SCL-90) by factor analysis could be replicated in a new sample. It was administered to 442 veterans undergoing psychiatric treatment at a VA psychiatric outpatient clinic. Factor analysis using the principal-components method yielded a factor structure different from those previously reported for other populations. The first factor extracted, Depression, explained 37% of the variance of the entire instrument, or more than eight times the variance explained by the second factor. Only five of the nine reported SCL-90 symptom subscales emerged in this study; the Anxiety and Psychoticism subscales disappeared, and the Paranoia and Interpersonal Sensitivity subscales merged. In this population the instrument seems to measure a single global distress factor instead of nine independent symptom subscales as reported previously. This finding was corroborated by the fact that depressed, anxious, and schizophrenic patients showed no differences in SCL-90 symptom profile shapes, although they did differ in overall symptom intensity.

Adult↗
PubMed1983

Changes in blood flow close to subcutaneous insulin injection sites in stable and brittle diabetics.

Photoelectric plethysmography (PPG) was used to investigate blood flow changes close to superficial subcutaneous injection sites. As a validation procedure, the PPG response to subcutaneous injection of a known hyperemic agent, prostaglandin E1 (10(-5) M), was shown to correlate strongly with subcutaneous blood flow changes estimated by the established technique of 133Xe washout. Changes in blood flow over the subcutaneous injection sites of insulin (Actrapid) and insulin diluent were measured by photoelectric plethysmography in six nondiabetics and in six stable and seven brittle insulin-dependent diabetics. In all subject groups, an acute increase in local blood flow was seen within 2 min of both insulin and diluent injections, probably caused by injection trauma. At diluent injection sites, this acute hyperemia faded rapidly, blood flow returning to preinjection levels within 15-20 min, and there was no further increase in blood flow in any of the subjects. Insulin injected into the nondiabetics and stable diabetics caused a pronounced increase in local blood flow, sustained for at least 60 min after injection. In the brittle diabetics, however, there was no prolonged local hyperemia, the response being significantly less than that seen in both the nondiabetics and the stable diabetics. Insulin-related hyperemia close to injection (or infusion) sites may be important in subcutaneous insulin absorption. Its near-absence in brittle diabetics may contribute to the impaired response to subcutaneous insulin characteristic of these patients.

Adult↗
PubMed1983

The long-term allografted rat islet. A histologic and immunohistologic study.

Long-term survival of islet allografts was achieved with an experimental model in the rat by the transplantation of islet/kidney composite grafts. Morphologic studies of these grafts incorporating immunocytochemistry have been made. Ther was minimal evidence of rejection of the transplanted islet tissue, which was composed almost entirely of insulin-containing cells. There were a few glucagon-containing cells, but pancreatic polypeptide-labeled and somatostatin-labeled cells were rarely seen. The endocrine cells were in different proportions and had no discernible relationship to one another, in contrast to those in nontransplanted islets. For successful clinical transplantation, it may be necessary to maintain normal relationships between endocrine cells.

Animals↗
PubMed1982

In vivo stability of nitrite and nitrosamine formation in the dog stomach: effect of nitrite and amine concentration and of ascorbic acid.

Formation of N-nitrosodimethylamine (NDMA) from the precursors nitrate and dimethylamine has been studied in the chronically fistulated dog stomach. Measurements have also been made as a function of time for nitrite stability and gastric pH, and a nonabsorbable marker has been used to correct for gastric emptying and dilution. In the fasting animal NDMA forms within minutes after addition of the reactants if the pH is below 5. The presence of food in the stomach slows the reaction, and the additional presence of ascorbic acid greatly depresses the amount of NDMA formed. The concentration of nitrite in gastric juice declines rapidly after its introduction, but the concentration of NDMA declines even more rapidly than nitrite. This suggests that NDMA is probably rapidly absorbed directly from the dog stomach, in contrast to earlier results in rodent experiments.

Absorption↗
PubMed1982

Multiple signals in STEM.

A brief description is given of the eight image signals that can be simultaneously recorded in digital form using an appropriate data recording system and high resolution STEM; this involves a set of detectors covering bright and dark field. Details are provided of the collection and manipulation of image data for STEM, including on-line estimation of off-focus distance, on-line assessment of astigmatism, on-line signal to noise ratio in any or all detectors; examples of all three procedures are given. The use of the data recording system is discussed together with some aspects of image display, including the use of colour. A method is introduced of providing, using the appropriate hardware, a prescribed colour map (image intensity converted to colour) using replaceable PROMS. Two off-line procedures are considered. One is the Karhunen-Loeve transform and its application to bringing together the information contained within the multiple signals, and the other is the discrete cosine transform by which the storage problem for digital image storage may be reduced, according to the image, by between 15 and 30 times.

Animals↗
PubMed1982

Islet changes induced by hyperglycemia in rats. Effect of insulin or chlorpropamide therapy.

To investigate the effect of hyperglycemia on normal islets, rats were made diabetic by a 95% partial pancreatectomy and treated with insulin, saline, or chlorpropamide for 3 mo. Histologic examination and morphometry of the residual pancreas showed islet enlargement and fibrosis that correlated with the mean lasting plasma glucose during the experimental period. Treatment of diabetes with insulin prevented the islet disorganization. The B-cell area per islet remained constant and was not affected by hyperglycemia. Chlorpropamide had little effect on the fasting plasma glucose or islet structure, and no "beta cytotrophic" effect was seen. Chronic hyperglycemia induces islet damage that may affect residual B-cell function in diabetes.

Animals↗
PubMed1982

High pressure liquid chromatographic determination of cyclosporin-A in human plasma.

Periodic monitoring of plasma drug concentrations has been suggested as a means whereby the toxicity of Cyclosporin A (CyA) can be reduced in patients undergoing bone marrow transplantation. We have developed a sensitive and specific method for the determination of CyA in plasma using reverse phase high pressure liquid chromatography (HPLC). Cyclosporin D was used as the internal standard. The lower limits of detection are 100 ng/ml in biological fluids and 20 ng per injection onto the column. We have analyzed plasma samples from patients who received CyA at doses which ranged from 8 to 15 mg/kg/day. Although all patients experienced toxic or therapeutic effects, plasma concentrations of CyA were consistently less than 100 ng/ml when analyzed by this method. We conclude that analytical methods currently available for the detection of CyA are unsuitable for the monitoring of patients who receive this agent.

Chromatography, High Pressure Liquid↗
PubMed1981

Stimulation of production of prostaglandin E in gingival cells exposed to products of human blood mononuclear cells.

1. Supernatant media from cultures of unstimulated human peripheral blood mononuclear cells contained one or more factors that increased by several hundred-fold the production of prostaglandin E by fibroblast-like cells derived from both inflamed and normal human gingival tissue. 2. This stimulation occurred in a dose-dependent manner and was completely inhibited by 14 microM-indomethacin. 3. Responsiveness to the factor declined as the age of the cell culture increased. 4. An increase in prostaglandin E production was first observed after a 2h exposure to the mononuclear cell factor(s) and could be prevented by cycloheximide. 5. Brief exposure (0.5 and 1.0 h) to mononuclear cell factor did not increase prostaglandin E production by the cells in a subsequent 72 h incubation in the absence of mononuclear cell factor. 6. Addition of arachidonate (10 microM and 15 microM) further enhanced stimulation of prostaglandin E production in response to mononuclear cell factor. 7. The stimulatory activity was resistant to digestion by trypsin, but was heat-labile, so that only 17% remained after treatment at 56 degrees C for 30 min.

Arachidonic Acid↗
PubMed1981

Solitary ulcer of the rectum--or is it? A report of 6 cases.

Solitary ulcer of the rectum is an unusual disorder which presents only occasionally to the individual clinician. While the histopathological features are characteristic, the wide variety of naked eye appearances of lesions which the syndrome produces may make for clinical confusion, particularly since the lesions may be neither solitary nor ulcerated. We present to the Victoria Infirmary, Glasgow, over the period 1969-79 which illustrate the diagnosis dilemma and variety of lesions encountered.

Adult↗
PubMed1981

An investigation into the origin and nature of 'amyloid' in a calcifying epithelial odontogenic tumour.

Fresh and fixed tissue from a resection specimen of a calcifying epithelial odontogenic tumour (CEOT) was prepared for histological, histochemical, immunological and biochemical investigation in order to study the nature of the amyloid-like material. The fixed tissue gave positive reactions with Congo-red, Thioflavin T and the dimethylamino benzene (DMAB)-method for tryptophan. The diazotization-coupling (DC) method for tyrosine was negative. The major protein purified from the unfixed tissue by sequential gel filtration had a molecular weight of 9,800. The amino acid analysis of this protein had similarities with tuft enamel protein, immune amyloid and the variable light chain component (VK). From the data obtained in this study, it is not possible to determine the precise nature of the amyloid-like material in this CEOT. However, the results do support the concept that 'amyloid' should be considered as a term describing a broad group of related proteins.

Adult↗