457 research outputs found

    Prostaglandin effects in the neuroendocrine mammalian brain

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    Publishers' versionThe original publication is available at http://www.samj.org.zaVarious prostaglandins (PGs) have been found in several areas of the brain. PGs of the E series have been found in the pituitary and pineal glands and the median eminence, and they have been shown to influence hypothalamic endocrine-release characteristics and release of melatonin from the pineal gland. It has been suggested that they may act, along with membrane phospholipids, as a link between neuronal depolarization, calcium uptake and neurotransmitter release. They may also influence postsynaptic effects of neurotransmitters. These latter effects may be due to interaction with membrane phospholipid- and cyclic nucleotide-induced changes of specific protein kinases. The PGs may act as intracellular mediators of neuro-endocrine control.Publishers' versio

    Sample size determination for external pilot cluster randomised trials with binary feasibility outcomes:a tutorial

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    Abstract Justifying sample size for a pilot trial is a reporting requirement, but few pilot trials report a clear rationale for their chosen sample size. Unlike full-scale trials, pilot trials should not be designed to test effectiveness, and so, conventional sample size justification approaches do not apply. Rather, pilot trials typically specify a range of primary and secondary feasibility objectives. Often, these objectives relate to estimation of parameters that inform the sample size justification for the full-scale trial, many of which are binary. These binary outcomes are referred to as “feasibility outcomes” and include expected prevalence of the primary trial outcome, primary outcome availability, or recruitment or retention proportions. For pilot cluster trials, sample size calculations depend on the number of clusters, the cluster sizes, the anticipated intra-cluster correlation coefficient for the feasibility outcome and the anticipated proportion for that outcome. Of key importance is the intra-cluster correlation coefficient for the feasibility outcome. It has been suggested that correlations for feasibility outcomes are larger than for clinical outcomes measuring effectiveness. Yet, there is a dearth of information on realised values for these correlations. In this tutorial, we demonstrate how to justify sample size in external pilot cluster trials where the objective is to estimate a binary feasibility outcome. We provide sample size calculation formulae for a variety of scenarios, make available an R Shiny app for implementation, and compile a report of intra-cluster correlations for feasibility outcomes from a convenience sample. We demonstrate that unless correlations are very low, external pilot cluster trials can be made more efficient by including more clusters and fewer observations per cluster

    LP (a) levels and apo (a) phenotypes in urban black South African men

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    CITATION: Carstens, M. E., Burgess, L. J. & Taljaard, J. J. F. 1998. LP (a) levels and apo (a) phenotypes in urban black South African men. South African Medical Journal, 88:139-142.The original publication is available at http://www.samj.org.zaObjective. To investigate the lipoprotein (a) (Lp (a)) levels and apolipoprotein (a) (apo (a)) phenotypes in a group of urban black South African men. Design. Cross-sectional design. Setting. Lead acid battery plant, East London, Eastern Cape. Participants. Blood samples from a study on the association between lead and renal failure were kindly donated for the present study and 111 of the donors participated (K Steyn - personal communication). Outcome measures. Lp (a) levels and apo (a) phenotypes. Results. Three groups were identified: those with normal ( 700 U/l) plasma Lp (a) concentrations. Nine apo (a) phenotypes and 26 combinations thereof could be discerned. Apart from the single- and double-band phenotypes described before, triple-band phenotypes were also present. As the Lp (a) values increased, the relative frequency of the single-band phenotype decreased, whereas the relative frequency of the double-band phenotype increased. The relative frequency of the triple-band phenotype was highest in the group with high Lp (a) concentrations. No correlation was evident between the size of the apo (a) isoforms and the Lp (a) concentrations. Conclusions. Raised plasma Lp (a) levels have been associated with coronary heart disease (CHD). In addition, it has been proposed that the apo (a) gene determined plasma Lp (a) concentrations. These studies were performed using plasma from white subjects. CHD is uncommon in black South Africans. The reason may be that, given the lack of relationship between the size of the apo (a) isoforms and the Lp (a) concentrations observed in the present study, factors other than the isoform size may determine the Lp (a) levels in this particular ethnic group.Publisher’s versio

    LP (a) levels and apo (a) phenotypes in urban black South African men

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    Objective. To investigate the lipoprotein (a) (Lp (a)) levels and apolipoprotein (a) (apo (a)) phenotypes in a group of urban black South African men.Design. Cross-sectional design.Setting. Lead acid battery plant, East London, Eastern Cape.Participants. Blood samples from a study on the association between lead and renal failure were kindly donated for the present study and 111 of the donors participated (K Steyn - personal communication).Outcome measures. Lp (a) levels and apo (a) phenotypes.Results. Three groups were identified: those with normal (<300 U/I), intermediate (300 - 700 U/I) and high (> 700 U/I) plasma Lp (a) concentrations. Nine apo (a) phenotypes and 26 combinations thereof could be discerned. Apart from the single- and double-band phenotypes described before, triple-band phenotypes were also present. As the Lp (a) values increased, the relative frequency of the single-band phenotype decreased, whereas the relative frequency of the double-band phenotype increased. The relative frequency of the triple-band phenotype was highest in the group with high Lp (a) concentrations. No correlation was evident between the size of the apo (a) isoforms and the Lp (a) concentrations.Conclusions. Raised plasma Lp (a) levels have been associated with coronary heart disease (CHD). In addition, it has been proposed that the apo (a) gene determined plasma Lp (a) concentrations. These studies were performed using plasma from white subjects. CHD is uncommon in black South Africans. The reason may be that, given the lack of relationship between the size of the apo (a) isoforms and the Lp (a) concentrations observed in the present study, factors other than the isoform size may determine the Lp (a) levels in this particular ethnic group

    Accommodating quality and service improvement research within existing ethical principles

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    Funds were provided by a Canadian Institute of Health Research grant (Nominated PI: Monica Taljaard, PJT – 153045). Funds were also generously provided by Charles Weijer, who is funded by a Tier 1 Canadian Research Chair.Peer reviewedPublisher PD
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