1
views
0
recommends
+1 Recommend
1 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found

      Melatonin and the Influence of the Pineal Gland on Timing of the LH Surge in Rats

      , ,

      Neuroendocrinology

      S. Karger AG

      Light exposure, Pineal gland, Melatonin, LH surge

      Read this article at

      ScienceOpenPublisherPubMed
      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          The purpose of this study was to determine if the temporal relationship between the LH surge and the photo-period is influenced by melatonin and the pineal gland in the rat. The timing of melatonin synthesis and of preovulatory LH release is reciprocally related; and since melatonin blocks LH secretion, it was hypothesized that the pineal ‘hormone’ contributes normally to termination of the LH surge. To test this hypothesis, we examined the temporal pattern of phasic LH secretion after altering pineal activity in rats with regular estrous cycles. Termination of the LH surge was delayed in rats exposed to a photophase acutely prolonged into the night of proestrus; a treatment which delays melatonin synthesis. On the other hand, the LH surge terminated normally despite extended light exposure, if the rats were injected with melatonin at 19.00 h, when the dark phase usually begins. Melatonin injections during the standard photophase, i.e. at 13.00 or 17.00 h, blocked or prematurely terminated the LH surge, respectively. However, these effects probably do not represent a physiological function of melatonin, since its synthesis does not accelerate normally until after dark. 5 out of 14 pinealectomized rats showed altered patterns of preovulatory LH secretion 2 months after surgery. Since melatonin has been reported to block serotonin receptors, and serotonin stimulates phasic secretion of LH, we tested the ability of quipazine, a serotonin receptor agonist, to antagonize the inhibitory effect of melatonin on the LH surge. Quipazine given at 15.30 h blocked the inhibitory effect of melatonin administered at 16.00 h. The serotonin agonist partially restored LH levels in proestrous rats when it was given 30 min after melatonin. Therefore, the inhibitory effect of melatonin on phasic secretion of LH may result from an action upon serotonin-containing neurons. These findings taken together suggest that the pineal gland, ostensibly through the action of melatonin, contributes to termination of phasic LH secretion and thereby participates in entrainment of the LH surge to the photoperiod in the female rat.

          Related collections

          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1982
          1982
          26 March 2008
          : 35
          : 1
          : 37-42
          Affiliations
          Department of Anatomy and Sanders-Brown Research Center on Aging, University of Kentucky Medical Center, Lexington, Ky., USA; Department of Physiology-Anatomy, University of California, Berkeley, Calif., USA
          Article
          123352 Neuroendocrinology 1982;35:37–42
          10.1159/000123352
          7202130
          © 1982 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: 6
          Categories
          Original Paper

          Comments

          Comment on this article