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      Inhibitory Effect of Melatonin on Gonadotropin-Releasing Hormone-Induced Ca 2+ Oscillations in Pituitary Cells of Newborn Rats

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          Abstract

          The effect of melatonin on the gonadotropin-releasing-hormone (GnRH)-induced oscillatory rises in intracellular calcium concentration, [Ca<sup>2+</sup>]<sub>i</sub>, was studied in cultured cells from the anterior pituitary gland of 6- to 8-day-old rats. GnRH-induced [Ca<sup>2+</sup>]<sub>i</sub> oscillations were recorded indirectly by monitoring the activity of apamin-sensitive Ca<sup>2+</sup>-activated K<sup>+</sup> channels using the perforated patch-clamp technique and fast microperfusion system. Melatonin (1 n M) inhibited the initiation or attenuated the amplitude of oscillatory current responses induced by 10 n M GnRH in 72% of GnRH-sensitive cells. Analysis of the melatonin dose-inhibition relationship showed that melatonin inhibited the initiation of [Ca<sup>2+</sup>]<sub>i</sub> oscillations with IC<sub>50</sub> = 0.35 n M. In partially inhibited cells, melatonin reduced the GnRH-induced current amplitude by 55% on the average, prolonged the delay in onset of response to GnRH and decreased the frequency of oscillations. Once initiated by GnRH, the amplitude and frequency of oscillatory currents was inhibited by melatonin after a latency of 10–30 s. These effects of melatonin were fully reversible. After pretreatment of neonatal gonadotropes with pertussis toxin, no inhibition by melatonin was observed. The inhibitory effect of melatonin on initiation, amplitude and frequency of GnRH-induced oscillatory current persisted in the absence of external Ca<sup>2+</sup>. Melatonin alone did not induce any transmembrane current or membrane potential changes. These observations suggest that melatonin reduces GnRH-induced calcium mobilization from intracellular stores.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1997
          1997
          09 April 2008
          : 65
          : 4
          : 276-283
          Affiliations
          Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
          Article
          127185 Neuroendocrinology 1997;65:276–283
          10.1159/000127185
          9142999
          © 1997 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: 8
          Categories
          Neuroendocrinology of Melatonin

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