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      Somatostatin Inhibits Alpha-2-Adrenergic-Induced Secretion of Growth Hormone-Releasing Hormone

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          Abstract

          The purpose of this experiment was to determine the role of growth hormone-releasing hormone (GHRH) and somatostatin (SRIH) neurons in mediating α<sub>2</sub>-adrenergic receptor-induced stimulation of growth hormone (GH) secretion in cattle. Our first objective was to determine if stimulation of α<sub>2</sub>-adrenergic receptors increases activity of GHRH neurons in the arcuate nucleus (ARC) and/or decreases activity of SRIH neurons in periventricular (PeVN) and ARC nuclei. Clonidine (an α<sub>2</sub>-adrenergic agonist) or vehicle (saline) were injected i.v. into steers and dual-label immunohistochemistry was performed to quantify the number of GHRH and SRIH neurons expressing Fos and Fos-related antigens (Fos/FRA) as markers of neuronal activity. Clonidine increased concentrations of GH in serum and decreased activity of SRIH neurons in the PeVN, but not in the ARC. Clonidine did not alter activity of GHRH neurons in the ARC. Our second objective was to determine if clonidine decreases secretion of SRIH from perifused slices of hypothalami, which contain perikarya and terminals of GHRH and SRIH neurons, and from explants of hypophysial stalk alone, which contain only terminals of GHRH and SRIH neurons. Clonidine failed to alter release of GHRH or SRIH from hypothalamic slices, but stimulated release of GHRH from explants of hypophysial stalk. Blockade of SRIH receptors enabled clonidine to stimulate release of GHRH from slices of hypothalami, but also stimulated release of SRIH. These results suggest that α<sub>2</sub>-adrenergic-induced secretion of GH occurs via a dual mechanism involving inhibition of SRIH neurons in the PeVN and direct stimulation of GHRH release from axon terminals in the median eminence.

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          Most cited references 6

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          Distribution of α2-adrenergic receptor subtype gene expression in rat brain

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            Secretin receptor activity in rat gastric glands. Binding studies, cAMP generation and pharmacology

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              Feeding Reduces Activity of Growth Hormone-Releasing Hormone and Somatostatin Neurons

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                Author and article information

                Journal
                NEN
                Neuroendocrinology
                10.1159/issn.0028-3835
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                2001
                June 2001
                13 June 2001
                : 73
                : 6
                : 417-425
                Affiliations
                Departments of aAnimal Science and bPharmacology and Toxicology, Michigan State University, East Lansing, Mich., USA
                Article
                54660 Neuroendocrinology 2001;73:417–425
                10.1159/000054660
                11408783
                © 2001 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: 34, Pages: 9
                Categories
                Regulation of Pituitary Cells

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