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      Sex Steroid Regulation of Growth Hormone Secretion and Action

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          Abstract

          Evidence that oestrogen is involved in the regulation of the somatotrophic axis in adult humans is provided by the observations that mean growth hormone (GH) levels are higher in women than men, that the fall in GH and insulin-like growth factor-1 (IGF-1) with aging are correlated to oestradiol levels and that oestrogen increases the GH responses to provocative stimuli. To investigate whether oestrogen modulates GH secretion and action in adult life, we studied the impact of oestrogen replacement on circulating GH and IGF-1 levels in postmenopausal women. Since the liver is the major source of circulating IGF-1 and the oral route of oestrogen delivery causes nonphysiologic effects on hepatic proteins, we compared the effects of oral and transdermal routes of delivery. Oral ethinyl oestradiol administration resulted in a significant fall in mean IGF-1 levels and a threefold increase in mean 24-hour GH. Transdermal administration of 17β-oestradiol resulted in a slight increase in serum IGF-1 but no change in mean 24-hour GH levels. To determine whether differences in oestrogen type rather than in the route of delivery caused the different effects on the GH/IGF-1 axis, we compared the effects of three oral oestrogen formulations. Ethinyl oestradiol, conjugated equine oestrogen and oestradiol valerate each induced a fall in IGF-1 and a rise in mean 24-hour GH levels in postmenopausal women. To determine the significance of oestrogen-induced changes on IGF-1, we studied effects on markers of connective and bone tissue activity. We found that propeptide concentrations of type III and type I collagen, and osteocalcin rose and fell in parallel with IGF-1 during oral or transdermal oestrogen therapy. Oestrogen causes distinct, route-dependent effects on the somatotrophic axis. The dissociation of the GH/IGF-1 axis by the oral route is likely to arise from impaired hepatic IGF-1 production which causes increased GH secretion through reduced feedback inhibition. Oestrogen treatment may have longer-term metabolic effects on hypogonadal women exerted through effects on the somatotrophic axis.

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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
          978-3-8055-6280-5
          978-3-318-00020-7
          1663-2818
          1663-2826
          1996
          1996
          09 December 2008
          : 45
          : 1-2
          : 67-73
          Affiliations
          Garvan Institute of Medical Research, St. Vincent’s Hospital, Sydney, Australia
          Article
          184762 Horm Res 1996;45:67–73
          10.1159/000184762
          8742122
          © 1996 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: 7
          Categories
          Session 3: GH and Gonadal Hormones

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