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      Endocrine Secretions under Abnormal Light-Dark Cycles and in the Blind

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          Abstract

          Both endogenous and exogenous factors are involved in regulation of endocrine secretions. Among the exogenous ones, light plays an important role both in animals and in humans. Pineal gland mediates light action on the endocrine system, by means of variations of melatonin (MT) secretion. Here we discuss about the influence of abnormal light-dark cycles and in particular of blindness on pineal and pituitary secretions and on those of correlated glands. MT secretion is usually inhibited by light: thus it reaches the highest levels at night. Exposure to short or long photoperiod causes variations in circadian or infradian MT rhythmicity. Blind patients can show higher daytime levels with a phase-advanced or phase-delayed circadian rhythm. Lack of light stimulus affects cortisol rhythm shifting the zenith of secretion and inducing a free-running rhythm. Blindness can abolish nocturnal growth hormone (GH) peak and impair the GH response to some stimuli; moreover it impairs the growth of affected patients. Light stimulus influences favorably gonadal function both in animals and in man. In animals, sexual activity and gonadal function decline during the seasons with reduced luminosity. A similar finding has been described in women living in a region with a strong seasonal contrast in luminosity. Blindness can impair luteinizing hormone, follicle-stimulating hormone, prolactin and testosterone secretion in prepubertal boys causing pubertal delay or more severe hypogonadism; it can affect pubertal development and fertility in women. Light can influence thyroid function in animals. Lack of light stimulus in blind man seems to cause different effects on thyroid function before and after puberty. Increase of free thyroid hormone levels has been found in prepubertal but not in adult blind patients, probably due to a resetting of the treshold for thyrotropin feedback suppression after puberty in these patients.

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          Most cited references 4

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          Effects of melatonin on vertebrate circadian systems.

          In many species of vertebrates the pineal gland and its indoleamine hormone melatonin play central roles in the control of circadian rhythms, whereas in some species, the pineal gland appears to hold little importance. However, recent research indicates that the circadian rhythms of many species of reptiles, birds and mammals, including humans, are synchronized by the administration of exogenous melatonin. These studies have led to questions concerning the role of this hormone in circadian organization in general. Studies of the sites and mechanisms of melatonin action further indicate that melatonin may be an excellent pharmacological tool for research on the cellular mechanisms of circadian clock function and have pointed to the possibility that melatonin or melatonin analogues may be therapeutically useful for the control of circadian clock dysfunctions such as jet lag, shift-work syndrome and sleep disorders.
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            Circadian rhythm abnormalities in totally blind people: incidence and clinical significance

             R Sack (1992)
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              • Abstract: not found
              • Article: not found

              Blindness and menarche.

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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
                : 153-157
                Affiliations
                Institute of Endocrinology, Second University of Naples, Italy
                Article
                23163 Horm Res 1998;49:153–157
                10.1159/000023163
                9550117
                © 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
                References: 72, Pages: 5
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