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Biomedical subjects

A Clark

Publications and source records attributed to A Clark.

At least 217 records · Page 12Linked to original sources
PubMed1989

The use of various handwashing agents to decontaminate gloved hands.

It has been suggested that gloved hands could be washed between patient treatments in the dental surgery and gloves re-used, provided they are undamaged. A series of experiments are described, which evaluate the effectiveness of four handwashing agents at removing defined bacterial inoculae from two types of latex rubber glove, a dedicated dental procedure glove (Regent Biogel D) which has a rough surface and a smooth-surfaced examination glove (Microtouch). The four agents tested were povidone iodine (Betadine), chlorhexidine (Hibiscrub), 60% iso-propyl alcohol, and a detergent triclosan preparation (Kleenex washcream). The Biogel D gloves required slightly shorter washing times to eradicate organisms than the Microtouch gloves. It was found that washing with water alone reduced the organisms on gloves by 300-1000-fold, but a minimum washing time of 20 seconds with povidone iodine or chlorhexidine was required to eradicate all the organisms inoculated, except bacterial spores, from both glove surfaces. Povidone-iodine and chlorhexidine were more effective washing agents than iso-propyl alcohol and triclosan soap.

1-Propanol↗
PubMed1989

Buffering of muscle tissue PO2 levels by the superposition of the oxygen field from many capillaries.

High resolution measurement in both exercised skeletal and cardiac tissue made radially outward from capillaries and longitudinally parallel to capillaries by Gayeski and Honig (1986, 1986a,b) and Honig and Gayeski (1987) indicate shallow variation of tissue PO2 and the absence of strong causal relation between the PO2 at a point and the proximity of that point to the nearest active capillary. Proposed as a model for the analysis of this tissue PO2 distribution, so contrary to the expectations of Krogh type models, are a class of multicellular tissue cylinder models. Each cylinder is penetrated by many parallel capillaries. In order to better represent the natural irregularities of the skeletal and cardiac tissue both with regard to radial placement and the stagger of the capillary inlets, the following types of models both with and without yoglobin are examined: regular square arrays where the capillary PO2 levels are random, uniform capillary PO2 levels but random capillary positions, and those with both the capillary PO2 levels and the positions are random. The results of the model calculations show that the superposition of the oxygen diffusion fields of all the capillaries produce a tissue PO2 distribution with the properties: (1) lower tissue PO2 levels than those predicted by Krogh theory, (2) significant non-local contributions to the PO2 at a point in the tissue which greatly reduces this correlation between PO2 at a point and its proximity to an active capillary, (3) shallow transcellular PO2 variation.

Animals↗
PubMed1989

How phosphocreatine buffers cyclic changes in ATP demand in working muscle.

1. Spatial buffering is hardly necessary for maintaining ATP concentration. 2. Temporal buffering may be essential to defend concentration of products of ATP hydrolysis. ADP would vary 4-fold and AMP would vary 16-fold during a single twitch without buffering. 3. The principal function of the transphosphorylating reaction may be to buffer temporally the concentrations of controlling reactants.

Adenosine Triphosphate↗
PubMed1989

Localisation of islet amyloid peptide in lipofuscin bodies and secretory granules of human B-cells and in islets of type-2 diabetic subjects.

Islet amyloid peptide (or diabetes-associated peptide), the major component of pancreatic islet amyloid found in type-2 diabetes, has been identified by electron-microscopic immunocytochemistry in pancreatic B-cells from five non-diabetic human subjects, and in islets from five type-2 diabetic patients. The greatest density of immunoreactivity for islet amyloid peptide was found in electron-dense regions of some lysosomal or lipofuscin bodies. The peptide was also localised by quantification of immunogold in the secretory granules of B-cells, and was present in cytoplasmic lamellar bodies. Acid phosphatase activity was also demonstrated in these organelles. Immunoreactivity for insulin was found in some lysosomes. These results suggest that islet amyloid peptide is a constituent of normal pancreatic B-cells, and accumulates in lipofuscin bodies where it is presumably partially degraded. In islets from type-2 diabetic subjects, amyloid fibrils and lipofuscin bodies in B-cells showed immunoreactivity for the amyloid peptide. Abnormal processing of the peptide within B-cells could lead to the formation of islet amyloid in type-2 diabetes.

Adolescent↗
PubMed1989

Treatment of supratentorial high grade gliomas with split course high fractional dose postoperative radiotherapy.

Ninety-two patients with malignant supratentorial gliomas diagnosed from 1977 to 1983 received split course external beam radiotherapy. The initial course of radiation consisted of 3000 cGy whole brain in ten fractions 5 days a week. After a 2-week rest, treatment was continued to a portal restricted to the computerized tomography scan demonstrated abnormality plus a margin for an additional 2100 cGy (total 5100 cGy/17 fx/36 days). The optic chiasm and hypothalamus were excluded from the high dose region. Following review of all pathologic specimens, three patients with grade II glioma, three lacking histologic confirmation, two unbiopsied and eleven not receiving the prescribed treatment were excluded from the survival analysis. No patients were lost to follow-up. Surviving patients were followed 85 months (median); range 68-125 months. All remaining patients were followed until death. The median actuarial survival for 73 grade III and IV patients was 12.5 months. The 5-year actuarial survival was 10%. The median survival for 54 grade IV patients was 10 months. The 5-year survival was 4%. For 19 grade III patients the median survival was 22.5 months. The 5-year survival was 26%. There was one long-term grade IV survivor (68 mos.) and four long-term grade III survivors (76, 85, 108, 125 mos). No patient developed optic nerve or chiasm injury. One patient, an 85 months survivor, had biopsy documented radionecrosis and hemiparesis. The incidence of necrosis among 62 patients alive 6 months or more (and therefore at risk of brain necrosis) is 1/62 (2%). The incidence among survivors is 1/5. The nominal standard dose for this regimen is 1749 ret. The predictive value of the "nominal standard dose" and "equivalent dose" formulae for brain necrosis is explored. We conclude (a) that this regimen provides a survival probability equivalent to conventional treatment for grade III and IV supratentorial gliomas, (b) that neither the equivalent nor nominal standard doses predicted the incidence of brain necrosis, (c) that the time dose schedule is well tolerated and has an acceptable risk-benefit ratio, (d) that its advantage to the patient is decreased time requirement and cost.

Adolescent↗
PubMed1989

The in-vitro inhibition of rat alloantigen presentation by immunotoxins--implications for allografting.

The removal of graft interstitial dendritic cells (IDC) prior to transplantation into a recipient has been shown to improve graft survival in a number of experimental studies. We report the in-vitro properties of two immunotoxins (IT) which could be used to deplete graft IDC when administered ex vivo by hypothermic perfusion in an experimental rat transplantation model. Ricin A chain (RAC) IT targeted at either class II major histocompatibility complex (MHC) molecules or leukocyte common antigens (LCA) were prepared. These IT had similar equilibrium constants, binding kinetics and inhibiting activity of cell-free protein synthesis. IT cytotoxicity was assessed by inhibition of alloantigen presentation by targeted low density spleen cells (LDSC) in a one way mixed lymphocyte culture (MLC). When LDSC were hypothermically incubated for 2 h with IT only the anti class II MHC IT inhibited the MLC and the maximum inhibition depended on the cell allotypes. The inhibition was increased to almost 100% when chloroquine was incorporated throughout the culture period.

Animals↗
PubMed1988

The projection from superior colliculus to cuneiform area in the rat. I. Anatomical studies.

Although the ipsilateral descending pathway is a major output projection of the superior colliculus, little is known of its functions. We therefore carried out two studies to investigate in rats the part of the ipsilateral projection that terminates in an area ventral to the inferior colliculus, referred to as the cuneiform nucleus. The first study, described here, used orthograde and retrograde tract-tracing techniques to locate the cells of origin and precise region of termination of the tectocuneiform pathway. The main findings were as follows. Injections of WGA-HRP into the superior colliculus gave terminal label in the cuneiform nucleus and also in surrounding structures which included central grey, the midbrain tegmentum bordering the parabigeminal nucleus, and the external nucleus of the inferior colliculus. As well as the strong ipsilateral projection, there was a much weaker contralateral one which crossed the midline in the tectal commissure. Label in the cuneiform nucleus was heaviest after injections into the medial deep layers. However, no clear evidence was found for topography within the tectocuneiform projection: cuneiform label varied in intensity rather than pattern of distribution with variation in the collicular location of the injection site. Injections of retrograde tracers into the cuneiform are a labelled large numbers of collicular cells, which were distributed mainly in the deep and intermediate grey layers. In agreement with the data from orthograde tracing, the heaviest concentration of labelled cells was found in the medial deep layers. This concentration extended into the adjacent dorsolateral part of central grey. A similar distribution of labelled cells was seen after injections into the structures next to the cuneiform nucleus that also receive a tectal projection. Comparison of this distribution with that obtained from injections into other parts of the ipsilateral projection, including dorsolateral basilar pons, suggested that the projection to the cuneiform area may arise from a distinct set of collicular output cells. The projection from the superior colliculus to the cuneiform nucleus and immediately adjacent areas may therefore be also functionally distinct, mediating a particular kind of tectally-elicited response. The lack of clear topography in the projection suggests that this response may not have precise spatial direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Pancreatic pseudotumors associated with multifocal idiopathic fibrosclerosis.

Two patients with multifocal idiopathic fibrosclerosis and sclerosing cholangitis developed biliary obstruction due to a fibrotic pancreatic pseudotumor. The masslike fibrosis mimicked pancreatic carcinoma on sonography and cholangio-pancreatography. In one patient sonography was successfully used to assess the response of the pseudotumor to corticosteroid therapy.

Cholangitis↗
PubMed1988

Hospitalization effect in acute mania.

We studied 31 patients meeting DSM-III criteria for bipolar affective disorder, manic type. All were treated in hospital, 18 on an open ward and 13 on a psychiatric intensive-care unit. Despite the use of only moderate doses of medication, dramatic clinical improvement was observed over the first 48 hours of treatment using the Brief Psychiatric Rating Scale and Beigel Mania Rating Scale as objective rating measures. Significantly greater improvement occurred in the psychiatric intensive-care unit in comparison to the open ward. We suggest that hospitalization effect is of prime importance in the early management of the acutely manic patient.

Adult↗
PubMed1988

Transfer factor in Hodgkin's disease: a randomized clinical and immunological study.

Transfer factor (TF) was prepared from buffy coats obtained from 493 units of blood taken from healthy donors, including individuals convalescent from various viral infections. It was administered to 22 of 47 patients with Hodgkin's disease undergoing treatment and consenting to take part in this randomized study to determine if TF would enhance their immunity and/or reduce the incidence of subsequent infections. Skin test reactivity was markedly enhanced in those patients receiving TF as opposed to placebo but other immunological assessments showed no significant differences between the groups. TF was not shown to be of benefit in the prevention of infections (including varicella/zoster).

B-Lymphocytes↗
PubMed1988

Calcitonin gene-related peptide and somatostatin inhibit insulin release from individual rat B cells.

Hormone secretion from single, rat pancreatic B cells was visualised by a reverse haemolytic plaque assay for C-peptide. Quantitative analysis of the size and number of haemolytic plaques indicated that exposure to 3, 5, 10 and 20 mM glucose resulted in a dose-dependent increase in both the magnitude of C-peptide, and thus, insulin release by individual B cells and the recruitment of activity secreting B cells. Somatostatin and calcitonin gene-related peptide, fragment 28-37 (CGRP28-37) were shown to inhibit glucose-stimulated insulin release as assessed by the size of individual plaques and the number of recruited B cells, and hence to reduce the total area of plaques formed. In the presence of 15 mM glucose, a dose-dependent effect of CGRP28-37 on the secretion of insulin was observed, with the size of plaques formed by individual B cells reduced at concentrations of CGRP28-37 between 10(-5) and 10(-11) M. Thus, both somatostatin and CGRP28-37 can act directly on individual B cells to inhibit their secretory response to increasing levels of glucose. We suggest that these peptides which can be immunolocalised in islet cells may have a role in the regulation of insulin secretion.

Animals↗
PubMed1988

Pathogenesis of NIDDM--a disease of deficient insulin secretion.

Type 2 diabetes is a familial disease and studies of both Caucasian and Japanese families have raised the possibility that a major susceptibility gene is involved. The majority of patients have both beta cell dysfunction and impaired insulin sensitivity but studies of relatives of Type 2 diabetic patients suggest that beta cell dysfunction is an early feature of the disease. Impaired insulin sensitivity, from acromegaly, Cushing's disease or steroid therapy, induces diabetes only in a small proportion of the population, and they may be those who have an inherited cell defect. We postulate that a single beta cell defect gene, on its own, may be insufficient to cause overt diabetes and would lead to life-long glucose intolerance unless associated with other defects such as impaired insulin sensitivity. The nature of such a postulated beta cell defect is uncertain. Whilst it has been reported to be specific to glucose, and not to non-glucose stimuli, this feature may be secondary to hyperglycaemia. The occurrence of islet amyloid in 70-90% of Type 2 diabetic patients, and rarely in the normal population, raises the possibility that amyloid deposition causing disruption of the islet is a factor which might affect beta cell function. Amyloid formation may be a primary abnormality or could be secondary to beta cell dysfunction induced by hyperglycaemia. A major susceptibility gene might predispose a proportion, perhaps 10-15%, of a Caucasian population towards diabetes. The subsequent development of diabetes in a particular patient is likely to depend on many factors including other genetic factors, a sedentary life style and obesity. In different populations different genetic influences may operate, including abnormalities of insulin receptor genes and glucose transporter genes, which may allow a beta cell abnormality to become expressed clinically.

Diabetes Mellitus, Type 2↗
PubMed1988

An A-chain ricin immunotoxin targeted against rat class II major histocompatibility complex molecules. In vitro and in vivo effects.

Studies reported here have demonstrated that an antirat class II major histocompatibility complex molecule A-chain ricin immunotoxin could specifically remove, in a dose-dependent manner, the cells capable of stimulating the rat mixed lymphocyte reaction, an in vitro model of transplant rejection. It was further demonstrated that administration of a monoclonal antibody against class II major histocompatibility complex molecules to isolated rat pancreas grafts by hypothermic perfusion resulted in the targeting of cells bearing class II major histocompatibility complex molecules. But administration of the immunotoxin to isolated pancreases in a similar manner did not prolong their survival when allografted across a major histocompatibility barrier.

Animals↗