Search

Swarm is ESA's (European Space Agency) first Earth observation constellation mission, which was launched in 2013 to study the geomagnetic field and its temporal evolution. Two Langmuir Probes (LPs) on board of each of the three Swarm satellites provide very accurate measurements of plasma parameters, which contribute to the the study of the ionospheric plasma dynamics. To maintain a high data quality for scientific and operational applications, the Swarm products are continuously monitored and validated via science-oriented diagnostics. This paper presents an overview of the data quality of the Swarm Langmuir Probes' measurements. The data quality is assessed by analysing short and long data segments, where the latter are selected sufficiently long to consider the impact of the solar activity. Langmuir Probes data have been validated through comparison with numerical models, other satellite missions, and ground observations. Based on the outcomes from quality control and validation activities conduced by ESA, as well as scientific analysis and feedback provided by the user community, the Swarm products are regularly upgraded. In this paper we discuss the data quality improvements introduced with the latest baseline, and how the data quality is influenced by the solar cycle. The main anomaly affecting the LP measurements is described, as well as possible improvements to be implemented in future baselines. [ABSTRACT FROM AUTHOR]

The mechanisms underlying the cardiac activities of synthetic growth hormone secretagogues (GHS) are still unclear. The natural ligand of the GHS receptors, i.e. ghrelin, classically binds the GHS receptor and exerts endocrine actions in acylated forms only; its cardiovascular actions still need to be investigated further. In order to clarify these aspects, we studied the effects of either the synthetic peptidyl GHS hexarelin (1 μM), or the natural ghrelin (50 nM) and the endogenous ghrelin derivatives des-Gln14-ghrelin (1–100 nM) and des-octanoyl ghrelin (50 nM), on the tension developed by guinea pig papillary muscle and on L-type Ca2+ current (ICa) of isolated ventricular cells. The binding of these molecules to ventricular cell membrane homogenates was also studied. We observed that all peptides reduced the tension developed at low frequencies (60–120 beats/min) in a dose-dependent manner. No alteration in cardiac contractility was induced by des-Gln14-ghrelin or des-octanoylated ghrelin when the endocardial endothelium had been removed or after cyclooxygenase blockade. Pretreatment with tyramine (2 μM) had no effect on the inotropic response induced by des-Gln14-ghrelin. No significant effect on ICa of isolated ventricular cells was observed in the presence of des-Gln14-ghrelin (100 nM). The order of potency on the tension of papillary muscle was: des-octanoyl ghrelin>ghrelin=des-Gln14-ghrelin>hexarelin. This gradient of potency was consistent with the binding experiments performed on ventricular membranes where either acylated or unacylated ghrelin forms, and hexarelin, recognized a common high-affinity binding site. In conclusion, ghrelin, des-Gln14-ghrelin and des-octanoyl ghrelin, show similar negative inotropic effect on papillary muscle; as des-octanoyl ghrelin is peculiarly devoid of any GH-releasing activity, the cardiotropic action of these molecules is independent of GH release. The binding studies and the experiments performed both on the isolated cells and on papillary muscle after endothelium removal or cyclooxygenase blockade indicate that the cardiotropic action of natural and synthetic ghrelin analogues reflects the interaction with a novel GHS receptor (peculiarly common for ghrelin and des-octanoyl ghrelin), leading to release of cyclooxygenase metabolites from endothelial cells, as indicated by direct measurement of prostacyclin metabolite 6-keto-PGF1α. [Copyright &y& Elsevier]

Among its pleiotropic actions, ghrelin modulates insulin secretion and glucose metabolism. Herein we investigated the role of ghrelin in pancreatic beta-cell proliferation and apoptosis induced by serum starvation or interferon (IFN)-gamma/TNF-alpha, whose synergism is a major cause for beta-cell destruction in type I diabetes. HIT-T15 beta-cells expressed ghrelin but not ghrelin receptor (GRLN-R), which binds acylated ghrelin (AG) only. However, both unacylated ghrelin (UAG) and AG recognized common high-affinity binding sites on these cells. Either AG or UAG stimulated cell proliferation through Galpha(s) protein and prevented serum starvation- and IFN-gamma/TNF-alpha-induced apoptosis. Antighrelin antibody enhanced apoptosis in either the presence or absence of serum but not cytokines. AG and UAG even up-regulated intracellular cAMP. Blockade of adenylyl cyclase/cAMP/protein kinase A signaling prevented the ghrelin cytoprotective effect. AG and UAG also activated phosphatidyl inositol 3-kinase (PI3K)/Akt and ERK1/2, whereas PI3K and MAPK inhibitors counteracted the ghrelin antiapoptotic effect. Furthermore, AG and UAG stimulated insulin secretion from HIT-T15 cells. In INS-1E beta-cells, which express GRLN-R, AG and UAG caused proliferation and protection against apoptosis through identical signaling pathways. Noteworthy, both peptides inhibited cytokine-induced NO increase in either HIT-T15 or INS-1E cells. Finally, they induced cell survival and protection against apoptosis in human islets of Langerhans. These expressed GRLN-R but showed also UAG and AG binding sites. Our data demonstrate that AG and UAG promote survival of both beta-cells and human islets. These effects are independent of GRLN-R, are likely mediated by AG/UAG binding sites, and involve cAMP/PKA, ERK1/2, and PI3K/Akt.

Background: Ghrelin, a natural growth hormone secretagogue (GHS), has been identified in prostate carcinoma cell lines., Objectives: To investigate the presence of ghrelin and its receptors in human prostate tumours and in DU-145, PC-3 and LNCaP prostate carcinoma cell lines, and to assess the effects of ghrelin and its more abundant circulating form, des-octanoyl ghrelin, on cell proliferation., Methods: Ghrelin and types 1a and 1b GHS receptor (GHS-R) were determined at the mRNA and protein levels by RT-PCR, in situ hybridization, immunohistochemistry and enzyme immunoassay in tissues, cell lines and culture medium. Ghrelin binding was determined by radioreceptor assay. The effects on cell proliferation were evaluated by growth curves., Results: Ghrelin mRNA was found in prostatic carcinomas and benign hyperplasias, but immunohistochemistry was negative. GHS-R1a and 1b mRNAs were absent from carcinomas, but GHS-R1b mRNA was present in 50% of hyperplasias. Ghrelin peptide and mRNA were present in PC-3 cells exclusively, whereas GHS-R1a and 1b mRNAs were expressed in DU-145 cells only. Specific [125I]Tyr4-ghrelin binding was detected in prostate tumour, DU-145 and PC-3 cell membranes and the binding was displaced by ghrelin, synthetic GHS and des-octanoyl ghrelin, which is devoid of GHS-R1a binding affinity and GH-releasing activity. Ghrelin and des-acyl ghrelin inhibited DU-145 cell proliferation, displayed a biphasic effect in PC-3 cells and were ineffective in LNCaP cells., Conclusions: Specific GHS binding sites, other than GHS-R1a and 1b, are present in human prostatic neoplasms. Ghrelin, in addition to des-acyl ghrelin, exerts different effects on cell proliferation in prostate carcinoma cell lines.