1,721,138 research outputs found
Ghrelin: more than a new frontier in neuroendocrinology.
No full textGhrelin, a peptide predominantly produced by the stomach, has been discovered as natural ligand of the growth hormone secretagogue receptor (GHS-R) type 1a. More recently, ghrelin attracted enormous interest as new orexigenic factor. However, ghrelin exerts several other neuroendocrine, metabolic and also non-endocrine actions (e.g. cardiovascular activities) that are explained by the widespread distribution of ghrelin and GHS-R expression. The existence of GHS-R subtypes and evidence that neuroendocrine but not all other ghrelin actions are dependent on acylation in serine 3 add further complexity to the system whose major physiological role remains to be definitely clarified. What we are learning from the studies about the control of ghrelin secretion is that it is mostly under metabolic control; the most important impact of ghrelin would, in turn, be metabolic. However, a recent study states that the ghrelin knockout (KO) mouse is not anorectic dwarf and this evidence clearly depicts a remarkable difference from the leptin KO mouse. Nevertheless, the original and fascinating ghrelin story as well as its potential pathophysiological implications in endocrinology and internal medicine are not definitely canceled by this evidence. Besides potential clinical implications for natural or synthetic ghrelin analogues acting as agonists or antagonists, open questions that are waiting for an answer are: how many are the ghrelin receptors? Is ghrelin the or a GHS ligand, i.e. are there other natural GHS-R ligands? Is there a functional balance between acylated and unacylated ghrelin forms that would play different actions? Within the next years these questions will find the appropriate answer and we'll know about the ghrelin system something more precise; this knowledge will more appropriately clarify the potential clinical perspectives
METABOLIC ACTIONS OF GHRELIN.
No full textGhrelin, a peptide predominantly produced by the stomach, has been discovered as natural ligand of the GH Secretagogue (GHS) receptor type 1a and supposed to play a major role in the control of somatotroph function. Instead ghrelin turned out to exert pleiotropic actions on several endocrine and non-endocrine target tissues consistently with its widespread expression distribution and
that of its receptors. Among its actions, particular attention has been focused on its central orexigenic effect,
and more recently on its peripheral metabolic influence on glucose and lipid metabolism.
Interestingly, some metabolic ghrelin actions are independent of its acylation supporting the hypothesis
of the existence of ghrelin receptors subtypes, distinct from the GHS-R1a. Consistently with its remarkable
metabolic impact, ghrelin secretion itself (70% in its non-acylated form) is mostly under metabolic control
being modulated by glucose, insulin and feeding. Recent studies suggest the hypothesis that ghrelin
system would play a role in type 2 diabetes, metabolic syndrome and atherogenesis
Ghrelin: from somatotrope secretion to new perspectives in the regulation of peripheral metabolic functions.
No full textGhrelin, a peptide predominantly produced by the stomach, has been discovered as natural ligand of the GH secretagogue (GHS) receptor type 1a (GHS-R1a), suggesting the existence a new endogenous modulator of somatotrope secretion. Subsequently, ghrelin turned out to exert pleiotropic actions, consistent with the widespread distribution of ghrelin and GHS-R expression in central and peripheral tissues. Despite that the binding to GHS-R1a requires ghrelin to be acylated in serine 3, some ghrelin actions are independent of such acylation; thus suggesting the possibility of the existence of other GHS-R subtypes. Ghrelin secretion (70% in its unacylated form) is mainly under metabolic control being modulated by glucose, insulin and feeding. On the other hand, ghrelin influences energy metabolism acting both as a central orexigenic factor and directly on the endocrine pancreas, liver and adipose tissue. Recently, another gastric hormone derived from the same ghrelin gene has been isolated and named obestatin. Obestatin in rats resulted in reduced food intake, jejunal contraction and body weight gain, via specific distinct receptors. Thus, all these data indicate that we are exploring a very complex system deeply involved in the modulation of metabolic functions, whose understanding will probably increase our knowledge about diabetes mellitus and the metabolic syndrome
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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