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      Intracerebral Immunoneutralization of Beta-Endorphin and Met-Enkephalin Disinhibits Release of Pituitary Luteinizing Hormone in Sheep

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          Abstract

          Experiments were conducted to determine if endogenously produced β-endorphin and met-enkephalin exert a physiological inhibition on luteinizing hormone-releasing hormone (LHRH) release in the central nervous system of sheep. Twenty-two mature ewes were implanted with unilateral guide tubes, through which matched infusion cannulae could be inserted without discomfort once daily for intracerebral (i.e.) infusion of three anti-opioid treatments: naloxone (50 µg in 20 µl), sheep antisheep β-endorphin (ABE; 20 µl of 1:25) or sheep anti-met-enkephalin (AME; 20 µl of 1:25) and of two control treatments: nonimmune sheep serum (20 µl of 1:25) or sheep antiporcine thyroglobulin (20 µl of 1:25). To detect abrupt disinhibition of LHRH release by anti-opioid treatments, serum luteinizing hormone (LH) was quantified at 10-min intervals for 1–2 h before and after each i.e. infusion. Complete trials consisted of 3–4 different anti-opioid or control i.e. infusions once daily at a single site over a period of 2–3 days during the luteal phase of recurring estrous cycles. Results were statistically evaluated within each ewe since complete trials were replicated 2–5 times within each ewe and because no 2 ewes could have i.e. infusions in identical locations. Anatomical generalizations were possible when LH responses to anti-opioid treatments were similar for several ewes with i.e. infusion sites in comparable brain regions. However, it was not possible to make such generalizations when infusion sites were not comparable in other ewes. In summary, naloxone consistently disinhibited LHRH/LH when infused into the mediobasal hypothalamus (n = 3), the anterior hypothalamic area (n = 4), the preoptic area (POA; n = 5) and the basal forebrain (BF; n = 5). Intracerebral immunoneutralization of β-endorphin with ABE disinhibited LHRH/LH release when infusions were into the rostral POA/nucleus accumbens region (n = 5) or into the anterolateral hypothalamus (n= 1). Infusions of ABE did not alter LH concentrations when administered into the BF(n = 7) or into areas of the hypothalamus other than the POA (n = 9). Intracerebral immunoneutralization of met-enkephalin with AME was not effective at any ABE-responsive sites (n = 6) or in the BF (n = 5), but it abruptly stimulated LHRH/LH release when infusions were into the anterior hypothalamic area (n = 2) or into the mediobasal hypothalamus (n = 1). Control infusions of antithyroglobulin serum did not alter patterns of serum LH concentrations. In summary, unilateral i.e. immunoneutralization of endogenous β-endorphin and of met-enkephalin in selected brain areas relieved the inhibition of LHRH release in luteal phase ewes. It is concluded that these two endogenous opioid peptides are involved in the physiological regulation of LHRH/LH release in the luteal phase ewe, and that they act at different sites of the central nervous system.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1990
          1990
          03 April 2008
          : 52
          : 4
          : 382-388
          Affiliations
          Department of Animal Sciences, Purdue University, West Lafayette, Ind., USA
          Article
          125609 Neuroendocrinology 1990;52:382–388
          10.1159/000125609
          2124663
          6f970b36-a26b-4d82-95d8-68704f426930
          © 1990 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.

          History
          : 06 October 1989
          : 13 April 1990
          Page count
          Pages: 7
          Categories
          Original Paper

          Endocrinology & Diabetes,Neurology,Nutrition & Dietetics,Sexual medicine,Internal medicine,Pharmacology & Pharmaceutical medicine
          β-Endorphin,Luteinizing hormone,Luteinizing hormone-releasing hormone,Naloxone,Endogenous opioid,Met-enkephalin

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