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      Calcitonin Inhibition of Prolactin Secretion in Lactating Rats: Mechanism of Action

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          Abstract

          The effects of intracerebroventricular (10 ng/rat) or intravenous (10 or 40 µg/15 min/rat) administration of salmon calcitonin (sCT) on the prolactin (PRL) response to suckling and the activity of tyrosine hydroxylase (TH) were examined in lactating rats. Plasma concentration of PRL increased dramatically in control rats after the onset of the suckling stimulus, while administration of sCT resulted in inhibition of PRL response to suckling. The action of sCT was much more effective with intracerebroventricular administration, which totally blocked PRL release, compared to intravenous administration. The intracerebroventricular administration of sCT increased TH activity of tuberoinfundibular dopamine neuron (TIDA) in the stalk-median eminence, as measured by DOPA accumulation, while completely suppressing the PRL response to suckling. Injection of α-methyl- p-tyrosine (α-MT; 50 mg/kg), an inhibitor of TH and thus dopamine synthesis, increased PRL levels, and suckling caused a further increase in plasma concentrations of PRL. Injection of sCT (intracerebroventricularly) did not inhibit the PRL response to suckling in the presence of a depletion of dopamine. These results suggest that sCT inhibition of PRL secretion in lactating rats is mediated mainly by TIDA neurons without involvement of other neuroendocrine mechanisms.

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          Most cited references 10

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          Neuroendrocrine regulation of prolactin release

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            The organization of tubero-hypophyseal and reticulo-infundibular catecholamine neuron systems in the rat brain.

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              Localization of calcitonin binding sites in rat central nervous system: evidence of its neuroactivity.

              The distribution of calcitonin (CT) binding sites in serial sections of the rat brain and spinal cord has been examined by an 'in vitro' autoradiographic technique using a radioisotope-sensitive sheet film and [125]salmon CT. Autoradiograms of the diencephalic region had the highest grain density throughout the entire hypothalamus, with the exception of the nuclei ventromedialis, posterior and mammillaris, which were not labeled at all. In the brainstem, large amounts of grains were found in the ventrolateral division of the periaqueductal gray, in the locus coeruleus, in the nucleus tractus spinalis nervi trigemini and in the raphe obscurus, pallidus and magnus, while a widespread and lower grain density was observed in the reticular formation. In the spinal cord the labeling was discretely localized in laminae IV, V and VI of the dorsal horn. The observed distribution of CT binding sites is closely related to the neuroendocrine and analgesic effects of exogenous CT and reinforces the concept of a possible neuromodulatory role proposed for the peptide at brain level.
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                Author and article information

                Journal
                NEN
                Neuroendocrinology
                10.1159/issn.0028-3835
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                2000
                May 2000
                22 May 2000
                : 71
                : 5
                : 327-332
                Affiliations
                Department of Molecular and Integrative Physiology, University of Kansas Medical Center, KansasCity, Kans., USA
                Article
                54553 Neuroendocrinology 2000;71:327–332
                10.1159/000054553
                10859495
                © 2000 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: 3, References: 36, Pages: 6
                Categories
                Regulation of Hypothalamic Neurons

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