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Biomedical subjects

S Gibson

Publications and source records attributed to S Gibson.

At least 109 records · Page 6Linked to original sources
PubMed1991

Mcm2 and Mcm3, two proteins important for ARS activity, are related in structure and function.

MCM2 and MCM3 are essential genes believed to play important roles in the initiation of DNA replication in Saccharomyces cerevisiae. Mutants defective in Mcm2 or Mcm3 are remarkably similar in phenotype. They both show an autonomously replicating sequence (ARS)-specific minichromosome maintenance defect, although their ARS specificities are not identical. In addition, these mutants exhibit a premitotic cell cycle arrest and an increase in chromosome loss and recombination. Genetic studies suggest that the two MCM gene products play interacting or complementary roles in DNA replication. Double mutants of mcm2-1 and mcm3-1 are inviable at the permissive growth temperature (23 degrees C) for each of the single mutants. Furthermore, overproduction of Mcm3 accentuates the deleterious effect of the mcm2-1 mutation, whereas overproduction of Mcm2 partially complements the mcm3-1 mutation. MCM2 encodes a protein of 890 amino acids containing a putative zinc-finger domain that is essential for Mcm2 function. Mcm2 shows striking homology to Mcm3 and three other proteins, Cdc46 of S. cerevisiae, and Nda4 and Cdc21 of Schizosaccharomyces pombe. The phenotypes of mutants defective in these proteins suggest that they belong to a protein family involved in the early steps of DNA replication.

Amino Acid Sequence↗
PubMed1991

Episodic ACTH and cortisol secretion in normal children.

The aim of this study was to determine the normal relationship between ACTH and cortisol secretion in children. Fourteen children (nine male, five female; median age 11.3 years) were hospitalized and blood samples were taken every 20 min for 24 h. A circadian rhythm was observed with median 0900 h and midnight ACTH values of 1.80 and less than 0.97 pmol/l, and for cortisol 296 and 62 nmol/l respectively. The median (range) areas under the curve for ACTH and cortisol were 29.7 (9.0-53.8) pmol/l/h and 5114 (3562-8630) nmol/l/h respectively. There were no significant differences detected for ACTH and cortisol secretion between males and females, or between prepubertal (n = 9) and pubertal subjects (n = 5). Using a novel form of time series analysis we have shown that both ACTH and cortisol are secreted with a dominant periodicity of 0.7-1.0 h, representing 24-34 secretory episodes of ACTH and cortisol in 24 h. For cortisol, but not ACTH, there is a significant secondary periodicity of 2-3.2 h. To look for shared periodicities we have used the technique of coherency. This reveals that for six of the children ACTH and cortisol are secreted with a significant shared periodicity of 0.8-1.0 h, and for a further five children a similar secondary shared periodicity is present. Therefore in normal children ACTH and cortisol secretion are interdependent and episodic but are not influenced by either pubertal status or gender.

Adolescent↗
PubMed1991

Regulation of ACTH secretory pathways in cultured pituitary cells.

Although chloroquine, an agent that disrupts regulated protein secretion, has previously been shown to decrease the adrenocorticotropic hormone (ACTH) secretory response to adenosine 3',5'-cyclic monophosphate or corticotropin-releasing factor (CRF) in AtT-20 and rat anterior pituitary cells, respectively, it has no effect on the response to vasopressin. The present study extended experiments with chloroquine to cultured sheep anterior pituitary cells, which have a greater maximum response to vasopressin. Chloroquine (200 microM) had no effect on basal ACTH secretion or on stimulation by vasopressin. In contrast to the rat, the net response to CRF was tripled by chloroquine in ovine cells. The effect of chloroquine on the response to CRF was more effective by coexposure of cells to CRF and chloroquine than by pretreatment with chloroquine. Monensin or vinblastine did not increase the ACTH response to CRF. The results indicate ACTH release in response to vasopressin is chloroquine insensitive in this way, can be dissociated from the mechanism that responds to CRF, and would be consistent with the CRF response mechanism involving pathways that can alter the secretory pool of ACTH. When chloroquine acts to increase the response to CRF, it is likely not to act by stabilizing the CRF-receptor complex.

Adrenocorticotropic Hormone↗
PubMed1990

Neural pathways in chronic pain.

The evidence for changes in function of the central nervous system in cases of chronic pain is persuasive. We are not dealing with a passively wired system but one which changes structure and function and even connectivity in response to incoming sensory information. Whether these changes are capable of reversal with time and treatment remains to be shown. An optimist would suggest that physiological changes without abnormalities are indeed capable of reversal given time and appropriate neural input that matches normal non-painful afferent stimulation. That this is feasible is suggested by strategies of management with successful outcomes in patients with chronic pain, especially when pain is due to intermittent or limited ongoing stimulation of nociceptors. Clinical experience suggests, however, that deafferentation pain syndromes where pain is a consequence of damage directly to the nervous system cannot be viewed in such an optimistic light. A great deal more knowledge is required of how both the peripheral and central nervous system react to damage before we will be in a position to manage this source of chronic pain successfully.

Afferent Pathways↗
PubMed1990

Improved detection of the histamine receptor on human peripheral blood mononuclear cells by crosslinking using tritiated as compared with radioiodinated histamine.

In order to detect histamine receptors on the surface of human peripheral blood mononuclear cells, the cells were incubated in the presence of radiolabelled histamine and then the bifunctional crosslinker disuccimidyl suberate was added in various concentrations. They were then solubilized with sodium dodecyl sulphate, boiled, reduced and the lysate separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both 3H and 125I-radiolabelled ligands bound to a 16 kDa band, to be defined although a much clearer and obviously unequivocal signal was obtained with 3H-labelled histamine. This molecule migrated with the same mass on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a 16 kDa subunit which had been purified on a histamine affinity column from Triton X-100 solubilized mononuclear cells, indicating it to be the ligand-binding subunit for the histamine receptor on these cells. For 3H, fluorography with Entensify was required to obtain an autoradiographic signal. Although 3H took much longer to give a signal than 125I, the considerable background, artefacts and heavy lane trailing seen with [125I] histamine were completely abrogated when [3H]histamine was used. In addition, the distinction between specific and nonspecific binding was more clearly seen using [3H]histamine. The modifications reported here which improve signal detection for 3H should encourage the use of tritiated ligands in radioreceptor crosslinking, particularly those of low molecular weight which might otherwise undergo steric modification due to iodination, this having the potential for interfering with receptor ligand binding.

Autoradiography↗
PubMed1990

Comparison of ACTH and ACTH precursor peptides secreted by human pituitary and lung tumour cells in vitro.

The molecular forms of ACTH secreted by established human small cell lung cancer (SCLC) cells and primary cultures derived from a bronchial carcinoid tumour, a pituitary adenoma and hyperplastic pituitary tissue have been characterized by Sephadex G-75 chromatography and quantified with two novel immunoradiometric assays for ACTH and ACTH precursor peptides. Pro-opiomelanocortin (POMC; Mr 31,000) and pro-ACTH (Mr 22,000) were secreted by all cell types. No smaller peptides were identified in the culture media from SCLC and bronchial carcinoid cells, implying a deficiency in the enzymes and/or intracellular organelles required for extensive POMC processing. A more heterogeneous profile of ACTH-containing peptides was produced by cells of pituitary origin, indicating more extensive proteolytic processing of POMC. However, the major peptide secreted by cells from a large aggressive pituitary adenoma was unprocessed POMC (Mr 31,000). These results suggest that both lung and pituitary cells in vitro retain their in-vivo pattern of POMC processing and provide valuable models in which to study the regulation of ACTH synthesis and secretion.

Adenoma↗
PubMed1989

Renal replacement therapy II.

The treatment of renal failure includes dietary modification, drug treatment and hormonal supplements as well as renal transplantation. The rationale for these therapies and the associated problems likely to present to the GP are given practical consideration.

Acute Kidney Injury↗
PubMed1989

Renal replacement therapy. I.

Virtually all patients with end-stage renal disease can achieve a better quality of life with renal replacement therapy. Given that a group practice with 10,000 patients may have two dialysis or transplant patients, it is important to know what is on offer. The first stage of renal replacement therapy is dialysis and the principles and problems are discussed here. In the next issue dietary management, drug therapy and the role of transplantation will be considered.

Humans↗
PubMed1989

Small cell lung cancer cell lines secrete predominantly ACTH precursor peptides not ACTH.

A panel of 18 well characterised human small cell lung cancer (SCLC) cell lines was assessed for the production of adrenocorticotrophin (ACTH) and its precursor peptides, pro-opiomelanocortin (POMC) and pro-ACTH. These precursor peptides were measured directly using a novel two-site immunoradiometric assay (IRMA) based on monoclonal antibodies, in conjunction with a similar IRMA for ACTH 1-39. Significant concentrations of ACTH precursors were secreted by 10 of the 18 cell lines (56%). The low levels of ACTH immunoreactivity detected in seven cell lines could be accounted for by the known cross-reactivity of precursors in the ACTH IRMA. This suggests there is little, if any, processing of ACTH precursors to ACTH. Cell pellet extracts contained undetectable or low levels of ACTH precursors and ACTH, indicating that these peptides are not stored intracellularly. During the growth of the SCLC cells in vitro ACTH precursors accumulated progressively in the culture medium. Thus the combination of a direct assay for the ACTH precursors and the panel of SCLC cell lines provides a valuable in vitro model for the expression of POMC in human tumours.

Adrenocorticotropic Hormone↗
PubMed1989

Comparison of the ACTH and cortisol responses to provocative testing with glucagon and insulin hypoglycaemia in normal subjects.

The glucagon stimulation test (GST) is often used to assess pituitary ACTH reserve, particularly when other tests are contra-indicated. In a preliminary investigation, in patients with pituitary disease, we failed to demonstrate the ACTH dependence of the cortisol response. We have therefore compared the ACTH, cortisol and glucose responses to glucagon (1 mg s.c.), insulin (0.2 U/kg i.v., ITT) and placebo in six healthy male volunteers, sampling every 10 min for 6 h. During the GST, mean +/- SD serum cortisol rose from 256 +/- 80 nmol/l to a peak of 481 +/- 164 nmol/l (range 289-717 nmol/l, P less than 0.01) in comparison with 280 +/- 81 nmol/l to 602 +/- 110 nmol/l (range 493-742 nmol/l) during the ITT (P less than 0.002). The mean peak cortisol levels achieved in the two tests did not differ significantly. In the GST, plasma ACTH rose from a mean basal value of 10.9 +/- 16.6 ng/l to a mean peak level of 123 +/- 76 ng/l (P less than 0.02) (ACTH ng/l x 0.225 = pmol/l). The corresponding values in the ITT were 7.1 +/- 16.2 ng/l and 263 +/- 91 ng/l (P less than 0.001). The mean peak ACTH level was significantly greater during the ITT (P less than 0.05). Thus the cortisol response was ACTH dependent in both the GST and the ITT in normal subjects. Furthermore, the ACTH response was of sufficient duration to be detected by the usual procedure of sampling every 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1989

Assessment of the potency of different standards in the immunoradiometric assay of ACTH.

There is no generally accepted human international reference preparation for ACTH. The different centres offering clinical ACTH measurement therefore select assay standards from the limited range of human-purified and synthetic preparations currently available. We have examined the relative potencies of three synthetic ACTH standards in comparison with the NIBSC human-purified 1-39 (code 74/555) in a two-site immunoradiometric assay (IRMA) for ACTH. All of the standards produced parallel curves in the IRMA but there was a wide variation in potency between the preparations giving highly significant differences in quality control and patients' ACTH results. Standards supplied by the National Hormone and Pituitary Programme, Bachem UK Ltd and Universal Biologicals Ltd gave lower ACTH results than results calculated using the NIBSC preparation. The potency differences between these standards emphasise the need for a reference preparation and, in the meantime, the necessity to define normal reference ranges for each laboratory.

Adrenocorticotropic Hormone↗
PubMed1989

Advantages of IRMA over RIA in the measurement of ACTH.

A technically simple and rapid two-site immunoradiometric assay (IRMA) for human ACTH, based on monoclonal antibodies (MAbs), was compared with a clinically validated ACTH radioimmunoassay (RIA). Both methods measure ACTH 1-39 in unextracted plasma and cross-react less than 0.5% with ACTH fragments. ACTH levels were assessed in 103 patient samples: for concentrations in the range 5.3-1000 ng/L, results by the two methods were significantly correlated (r = 0.82, n = 86, P less than 0.001). The IRMA was more sensitive and had a wider working range than the RIA (detection limits 5.3 ng/L (IRMA) vs 11 ng/L (RIA); CV less than 10% between 19 and 1000 ng/L (IRMA) and CV less than 15% between 30 and 400 ng/L (RIA). In two patients for whom discrepant results were obtained, measurement of ACTH by bioassay and ACTH precursors by direct IRMA demonstrated the greater accuracy of the ACTH IRMA result. The improved performance of the IRMA combined with its many practical advantages compared to RIA, make it ideal for use in detailed clinical and physiological studies which have previously been hampered by the poor reliability of ACTH measurement.

Adrenocorticotropic Hormone↗
PubMed1989

Can psychometric tools be used to analyse pain in a geriatric population?

Pain is both a sensory and an emotional experience. In a multidisciplinary pain management clinic for a geriatric population, pain and mood have been assessed prior to the initiation of management in 49 of 100 referred patients. Patients have been assessed clinically, for psychological disability using the profile of mood states (POMS) and a visual analogue scale for mood, for pain using the McGill pain questionnaire (short form), word descriptor scale and visual analogue scale and for activities of daily living (ADL) using the Disability and Impairment Interview Schedule and the Rapid Disability Rating Scale -2. All testing has followed initial screening to exclude dementia. For the group assessed by psychometric measures, median age was 75 years (range 56 to 91); 41 were female. Major pathologies were degenerative musculoskeletal disease (15), post-herpetic neuralgia (9), and psychiatric conditions (7). Intra-test item correlations were found to be significant for the McGill questionnaire and the POMS. Inter-test correlations were observed for pain measures (McGill present pain intensity with VAS pain, r = 0.67; with word descriptor, 0.64; p less than 0.001), for ADL measures (r = 0.53, p less than 0.001) and for measures of mood (VAS mood with POMS (depression), r = 0.45; p less than 0.001; with POMS (anxiety), r = 0.35; p less than 0.01. There was no significant correlation between measures of mood and pain on the McGill scale. The data to this time support the view that standard psychometric tools can be used reliably to evaluate pain, mood and activity in this population. Furthermore, it appears that mood and pain may be measured separately.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Mast cell protease release and mucosal ultrastructure during intestinal anaphylaxis in the rat.

Intestinal anaphylaxis is associated with disturbances in gut function that are antigen-specific and dependent on mast cell degranulation. Using an animal model of intestinal anaphylaxis, we have correlated alterations in water and electrolyte transport, associated with intraluminal challenge, with specific intestinal mucosal mast cell degranulation by following systemic as well as local release of rat mast cell protease II. This protease is specific for intestinal mucosal mast cells and is known to selectively attack type IV collagen, which is found in basement membranes. Intraluminal antigen challenge in sensitized animals dramatically increased serum and intraluminal levels of rat mast cell protease II. Serum levels continued to rise throughout the duration of antigen challenge. Although light microscopy of challenged intestine demonstrated little distortion of mucosal architecture, ultrastructural examination revealed significant disruption to the basement membrane and underlying collagenous matrix of the intestinal mucosa. Our findings indicate that during mucosal immunoglobulin E-mediated reactions, rat mast cell protease II is released and is associated with ultrastructural changes in the intestinal mucosa. The systemic appearance of this specific protease provides a serum marker of intestinal anaphylaxis.

Anaphylaxis↗
PubMed1988

Fusion of a Sendai mutant deficient in HN protein (ts271) with cardiolipin liposomes.

Sendai mutant ts271 contains less than 5% of the amount of HN glycoprotein found in wild-type Sendai. Fusion of this mutant with cardiolipin liposomes revealed no differences from the wild-type virus with regard to specific activity, pH dependence, or radiation inactivation. Target sizes of both mutant and wild-type viral proteins were determined by the radiation-induced disappearance of each band from an SDS-polyacrylamide gel and no differences were found. Of the viral proteins, only F had a target size corresponding to the monomer molecular weight, ca. 60 kDa, identical to the minimum unit previously determined by functional assay for Sendai virus-erythrocyte membrane fusion (K. Bundo-Morita, S. Gibson, and J. Lenard, Biochemistry 26, 6223-6227 (1987)). This provides additional evidence that F alone is the active protein mediating Sendai-erythrocyte fusion. It is concluded that the HN protein is unlikely to mediate any fusion reactions of the intact virions, either with biological membranes or with cardiolipin liposomes.

Cardiolipins↗
PubMed1988

Radiation inactivation analysis of fusion and hemolysis by vesicular stomatitis virus.

Radiation inactivation analysis was used to determine the size of the functional unit responsible for fusion of vesicular stomatitis virus (VSV) with cardiolipin or phosphatidylcholine-phosphatidylethanolamine (1:1) liposomes, and for VSV-induced hemolysis. When radiation-insensitive background values were subtracted, the calculated functional units for all three activities were similar, ranging from 866 to 957 kDa, equivalent to about 15 G protein molecules. This is in striking contrast to results of similar studies with influenza and Sendai viruses, in which the functional unit corresponded in size to a single fusion protein monomer, and suggests that VSV fusion may occur by a different mechanism.

Hemolysis↗