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3 results on '"Robson, Helen"'

1. Calcium and growth hormone secretion in the domestic fowl (Gallus domesticus)

Author

Robson, Helen

Subjects
590, C110 - Applied biology
Abstract

Extracellular calcium is a ubiquitous molecule required for secretagogue induced growth hormone release from somatotroph cells of the chicken anterior pituitary. Growth hormone release can be induced via different intracellular pathways and these in turn can act to produce a synergistic hormone release. This thesis sought to further characterise the intracellular and membrane dependent pathways involved in growth hormone release with regard to the regulation of calcium ion and other ion fluxes, and to determine the mechanism for GRF and TRH synergy in the domestic fowl. Growth hormone secretion from chicken somatotroph cells was dependent upon the extracellular calcium concentration and its subsequent influx into dispersed chicken somatotroph cells in vitro, which was blocked by voltage dependent calcium channel antagonists. Both parameters also demonstrated a dependence on extracellular sodium. TRH stimulated growth hormone release was similarly dependent on the influx of calcium from the extracellular space in dispersed chicken somatotroph cells in vitro. hpGRF-44/TRH synergy, however, failed to show a corresponding potentiated calcium influx with the synergistic growth hormone release - this response was merely additive with respect to the two secretagogues. The intracellular second messenger dbc-AMP produced similar responses, in the presence of the various modulatory agents, to those observed with hpGRF-44, although the maximal levels reached were lower. hpGRF-44 depolarised chicken somatotroph cells in vitro. The profile of changes in the membrane potential indicated the presence of sodium, calcium and potassium channels. Removal of extracellular sodium abolished hpGRF-44 induced depolarisation. Low and high extracellular calcium concentrations resulted in potentiated and reduced responses respectively. Repolarisation of the somatotroph cells was dependent on calcium and although none of the calcium dependent potassium channel antagonists affected the maximal depolarisation that was reached, apamin removed the ability of the cells to repolarisc and thus depolarisation was prolonged. In the presence of these agents an enhanced release of growth hormone was observed under conditions of a prolonged depolarisation whilst it was diminished when the depolarisation was shortened or abolished. It is therefore concluded that hpGRF-44 induced growth hormone release in chickens is dependent on the influx of extracellular calcium which in turn is dependent on a variety of mechanisms not least the voltage dependent calcium channels. Ion fluxes are also modulated via a hpGRF-44 induced depolarisation characterised by its sodium, calcium and potassium components and which are necessary for eliciting and maintaining the growth hormone release. Synergistic growth hormone release involves a mechanism other than a potentiated calcium influx and in short involves the integration of a complex array of intracellular events and pathways. A model is suggested which summarises the role of extracellular calcium in GH release from somatotroph cells of the domestic fowl integrating the regulatory mechanisms involved both at the membrane level and the intracellular level.

Published
1993

2. Albumin level and patient age predict outcomes in patients referred for gastrostomy insertion:internal and external validation of a gastrostomy score and comparison with artificial neural networks

Author

Leeds, John, McAlindon, Mark E., Grant, Julia, Robson, Helen E., Morley, Stephen R., James, Gary, Hoeroldt, Barbara, Kapur, Kapil, Dear, Keith, Hensman, James, Worden, Keith, Sanders, David S., Leeds, John, McAlindon, Mark E., Grant, Julia, Robson, Helen E., Morley, Stephen R., James, Gary, Hoeroldt, Barbara, Kapur, Kapil, Dear, Keith, Hensman, James, Worden, Keith, and Sanders, David S.

Abstract

Background: Significant mortality after gastrostomy insertion remains and some risk factors have been identified, but no predictive scoring system exists. Objective: To identify risk factors for mortality, formulate a predictive scoring system, and validate the score. Comparison to an artificial neural network (ANN). Design: Endoscopic database analysis. Setting: Six hospitals (2 teaching hospitals) in the South Yorkshire region, United Kingdom. Patients: This study involved all patients referred for gastrostomy insertion. Intervention: Generation of clinical scores to predict 30-day mortality in patients undergoing gastrostomy insertion. Main Outcome Measurements: Risk factors for 30-day mortality. Internal and external validation of the score. Comparison with an ANN. Results: Univariate analysis showed that 30-day mortality was associated with age, albumin levels, and cardiac and neurological comorbidities. Multivariate analysis showed that only age and albumin levels were independent. Modeling provided scores of 0, 1, 2, and 3 corresponding to 30-day mortalities of 0% (0-2.1), 7% (2.9-13.9), 21.3% (13.5-30.9), and 37.3% (24.1-51.9), respectively. Application of the scoring system at the other teaching hospital and the 4 district general hospitals gave 30-day mortality rates that were not significantly different from those predicted. Receiver operating characteristic curves for the score and the ANN were comparable. Limitations: Nonrandomized study. Score not used as a decision-making tool. Conclusion: The gastrostomy score provides an estimate of 30-day mortality for patients (and their relatives) when gastrostomy insertion is being discussed. This score requires evaluation as a decision-making tool in clinical practice. ANN analysis results were similar to the outcomes from the clinical score.

Published
2011

3. Decoupling the direct and indirect effects of nitrogen deposition on ecosystem function.

Author

Manning, Pete, Newington, John E., Robson, Helen R., Saunders, Mark, Eggers, Till, Bradford, Mark A., Bardgett, Richard D., Bonkowski, Michael, Ellis, Richard J., Gange, Alan C., Grayston, Susan J., Kandeler, Ellen, Marhan, Sven, Reid, Eileen, Tscherko, Dagmar, Godfray, H. Charles J., Rees, Mark, Manning, Pete, Newington, John E., Robson, Helen R., Saunders, Mark, Eggers, Till, Bradford, Mark A., Bardgett, Richard D., Bonkowski, Michael, Ellis, Richard J., Gange, Alan C., Grayston, Susan J., Kandeler, Ellen, Marhan, Sven, Reid, Eileen, Tscherko, Dagmar, Godfray, H. Charles J., and Rees, Mark

Abstract

Elevated nitrogen (N) inputs into terrestrial ecosystems are causing major changes to the composition and functioning of ecosystems. Understanding these changes is challenging because there are complex interactions between 'direct' effects of N on plant physiology and soil biogeochemistry, and 'indirect' effects caused by changes in plant species composition. By planting high N and low N plant community compositions into high and low N deposition model terrestrial ecosystems we experimentally decoupled direct and indirect effects and quantified their contribution to changes in carbon, N and water cycling. Our results show that direct effects on plant growth dominate ecosystem response to N deposition, although long-term carbon storage is reduced under high N plant-species composition. These findings suggest that direct effects of N deposition on ecosystem function could be relatively strong in comparison with the indirect effects of plant community change.

Published
2006

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