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      Evidence for Pineal Gland Modulation of the Neuroendocrine-Thyroid Axis

      Neuroendocrinology

      S. Karger AG

      Pineal gland, Melatonin, Thyroxin, Thyroid, Environmental lighting

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          Abstract

          Experiments with rats and hamsters have provided evidence for an inhibitory action of the pineal gland on the neuroendocrine-thyroid axis. While maintenance of these animals in short photoperiod results in reduced levels of circulating thyroxin (T4), pinealectomy restores the levels to normal. Recent studies suggest that an active pineal gland produces a substance which inhibits thyrotrophin-releasing hormone release from the hypothalamus. Several investigators have concluded that endogenous melatonin, produced in the pineal gland, could account for the inhibitory action of the pineal gland on blood T4 levels. Although melatonin administration has been reported to inhibit blood T4 levels in both rats and hamsters, under certain experimental conditions melatonin administration can be demonstrated to have a counter-antithy-rotrophic effect resulting in increased blood levels of T4 and thyrotrophin. Assay of blood levels of melatonin of rats and hamsters under various experimental conditions will be necessary to distinguish physiological from pharmacological effects of melatonin. Lesion studies as well as studies with melatonin implants in the brain, suggest that the site of action is in the anterior hypothalamus. The effects of melatonin on the neuroendocrine-thyroid axis are similar to its effects on the neuroendocrine-gonadal axis, leading to the hypothesis of a common site of action for the thyroid and gonadal effects of melatonin. Although many pineal ‘factors’ have been postulated to account for the action of this gland, an action of melatonin on the serotonergic system of the brain stem could account for the data.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1983
          1983
          26 March 2008
          : 36
          : 1
          : 68-78
          Affiliations
          Department of Anatomy, University of Manitoba School of Medicine, Winnipeg, Man., Canada
          Article
          123439 Neuroendocrinology 1983;36:68–78
          10.1159/000123439
          6338409
          © 1983 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
          Pages: 11
          Categories
          Progress in Neuroendocrinology

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