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      Effect of Seasonal Changes in Daylength on Human Neuroendocrine Function

      Hormone Research in Paediatrics

      S. Karger AG

      Circadian rhythm, Photoperiod, Season, Melatonin, Prolactin, Growth hormone, Cortisol, Light

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          Abstract

          The circadian pacemaker imposes stereotypic patterns of daily variation on the activity of human neuroendocrine systems. In a number of cases, these patterns exhibit waveforms that are characterized by distinct diurnal and nocturnal periods with relatively discrete transitions between them (corresponding to a biological day, a biological dusk, a biological night, and a biological dawn). In humans, for example, diurnal periods of absence of melatonin secretion, low prolactin secretion, and falling levels of cortisol alternate with nocturnal periods of active melatonin secretion, high prolactin secretion and rising levels of cortisol. In response to light, the circadian pacemaker synchronizes the timing of the biological day and night so that their timing and duration are appropriately matched with the timing and duration of the solar day and night. As the pacemaker carries out this function, it is able to adjust the duration of the biological day and night to match seasonal variation in the duration of the solar day and night. Thus, after humans have been chronically exposed to long nights (scotoperiods), the duration of nocturnal periods of active melatonin secretion, high prolactin secretion and rising levels of cortisol is longer than it is after they have been chronically exposed to short nights. Furthermore, the sleep-related peak of growth hormone secretion is half as high after exposure to long nights as it is after exposure to short nights. These responses to seasonal changes in duration of the natural scotoperiod are suppressed in most individuals – especially men – who live in modern urban environments in which they are exposed to artificial light after dark and artificial darkness during the daytime.

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          Author and article information

          Journal
          HRE
          Horm Res Paediatr
          10.1159/issn.1663-2818
          Hormone Research in Paediatrics
          S. Karger AG
          978-3-8055-6666-7
          978-3-318-00288-1
          1663-2818
          1663-2826
          1998
          March 1998
          16 March 1998
          : 49
          : 3-4
          : 118-124
          Affiliations
          Clinical Psychobiology Branch, National Institute of Mental Health, Bethesda, Md., USA
          Article
          23157 Horm Res 1998;49:118–124
          10.1159/000023157
          9550111
          © 1998 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: 17, Pages: 7
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