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      Leptin Stimulates Growth Hormone Secretion via a Direct Pituitary Effect Combined with a Decreased Somatostatin Tone in a Median Eminence-Pituitary Perifusion Study

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          Abstract

          The aim of this study was to examine the effect of recombinant human leptin on growth hormone (GH) secretion in perifused anterior pituitary slices from adult pigs. Anterior pituitary slices from sows were perifused and treated with recombinant human leptin (10 n M) and GH-releasing hormone (GHRH; 1 n M). In some experiments, pituitary slices were coincubated with stalk median eminence (SME). In a subset of the coincubation experiments, immunoneutralization of endogenous GHRH and somatostatin (SRIH) release was performed with antisera to GHRH and SRIH. Leptin increased GH secretion in pituitary slices alone (up to 100% vs. control at 40 min) as well as in pituitary slices coincubated with SME (up to 122% vs. control at 40 min). A significant difference was observed in GH secretion from pituitary slices when the tissue was coincubated with leptin and GHRH at a low concentration (0.1 n M), but not when GHRH was used at 1 and 10 n M. Furthermore, anti-SRIH antiserum increased GH release from pituitary slices in coincubation experiments with SME. Finally, SRIH secretion was significantly reduced by leptin (down by 35% vs. control from 0 to 30 min of treatment) in cultured SME. These data show that leptin is effective in stimulating GH secretion by acting at two different levels: (1) it stimulates GH secretion directly from pituitary slices, and (2) it reduces SRIH tone from the median eminence and, indirectly, increases GH secretion from the pituitary. These results support the hypothesis that leptin may be an interesting hormonal mediator of growth and related metabolic effects by acting directly on the hypothalamic-pituitary axis.

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          Most cited references 15

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          Design and synthesis of multi-haem proteins.

          A water-soluble, 62-residue, di-alpha-helical peptide has been synthesized which accommodates two bis-histidyl haem groups. The peptide assembles into a four-helix dimer with 2-fold symmetry and four parallel haems that closely resemble native haems in their spectral and electrochemical properties, including haem-haem redox interaction. This protein is an essential intermediate in the synthesis of molecular 'maquettes', a novel class of simplified versions of the metalloproteins involved in redox catalysis and in energy conversion in respiratory and photosynthetic electron transfer.
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            A nutrient-sensing pathway regulates leptin gene expression in muscle and fat.

            Leptin, the protein encoded by the obese (ob) gene, is synthesized and released in response to increased energy storage in adipose tissue. However, it is still not known how incoming energy is sensed and transduced into increased expression of the ob gene. The hexosamine biosynthetic pathway is a cellular 'sensor' of energy availability and mediates the effects of glucose on the expression of several gene products. Here we provide evidence for rapid activation of ob gene expression in skeletal muscle by glucosamine. Increased tissue concentrations of the end product of the hexosamine biosynthetic pathway, UDP-N-acetylglucosamine (UDP-GlcNAc), result in rapid and marked increases in leptin messenger RNA and protein levels (although these levels were much lower than those in fat). Plasma leptin levels and leptin mRNA and protein levels in adipose tissue also increase. Most important, stimulation of leptin synthesis is reproduced by either hyperglycaemia or hyperlipidaemia, which also increase tissue levels of UDP-N-acetylglucosamine in conscious rodents. Finally, incubation of 3T3-L1 pre-adipocytes and L6 myocytes with glucosamine rapidly induces ob gene expression. Our findings are the first evidence of inducible leptin expression in skeletal muscle and unveil an important biochemical link between increased availability of nutrients and leptin expression.
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              Unraveling the central nervous system pathways underlying responses to leptin.

              Here we summarize recent progress in the biology of leptin, concentrating on its central nervous system (CNS) actions. The product of the ob gene, leptin is a circulating hormone produced by white adipose tissue that has potent effects on feeding behavior, thermogenesis and neuroendocrine responses. Leptin regulates energy homeostasis, as its absence in rodents and humans causes severe obesity. We consider the physiological mechanisms underlying leptin action, along with several novel hypothalamic neuropeptides that affect food intake and body weight. The molecular causes of several other obesity syndromes are discussed to illuminate how the CNS regulates body weight. We describe neural circuits that are downstream of leptin receptors and propose a model linking populations of leptin-responsive neurons with effector neurons underlying leptin's endocrine, autonomic and behavioral effects.
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                Author and article information

                Journal
                NEN
                Neuroendocrinology
                10.1159/issn.0028-3835
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                2004
                May 2004
                10 June 2004
                : 79
                : 4
                : 221-228
                Affiliations
                aDepartment of Animal Production, Veterinary Biotechnology, Food Safety, University of Parma, Parma, bGeneral Medicine Division 1, University of Brescia, Brescia, cDIMORFIPA, University of Bologna, Ozzano Emilia, dEli Lilly Italia, Sesto Fiorentino, Florence, eDepartment of Veterinary Morphophysiology, University of Torino, Grugliasco, Italy; fHong Kong International School, Hong Kong
                Article
                78103 Neuroendocrinology 2004;79:221–228
                10.1159/000078103
                15153755
                © 2004 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 7, References: 43, Pages: 8
                Categories
                Regulation of Pituitary Cells

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