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      Progesterone-Like Effects of Estradiol on Reproductive Behavior and Hypothalamic Progestin Receptors in the Female Rat

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          Abstract

          During the rat estrous cycle, estradiol (E<sub>2</sub>) and progesterone (P) synergize to activate reproductive behavior. However, receptivity and proceptivity can be elicited by E<sub>2</sub> alone in ovariectomized (OVX) animals, particularly when E<sub>2</sub> doses are high. The purpose of this study was to determine the neuroendocrine mechanism by which E<sub>2</sub> elicits P-dependent reproductive behavior. Adult OVX females received estrogen treatment for 72 h, which consisted of 5 mm Silastic capsules containing 100% E<sub>2</sub> or 10% E<sub>2</sub>, or of 3 injections of estradiol benzoate (EB; 20 µg daily). At 72 h, some animals were sacrificed for nuclear progestin receptor (NPR) measurements, while others were tested for reproductive behavior. The remaining animals received 1 -mg injections of E<sub>2</sub>, P, moxestrol (Mox) or oil, and either were sacrificed 2 h later for NPR measurements or were tested 4 h later for reproductive behavior. A subset of the animals receiving 1 mg E<sub>2</sub> received concurrent administration of the protein synthesis inhibitor, anisomycin (ANI; 100 mg/kg). Acute administration of 1 mg of E<sub>2</sub> or P significantly elevated proceptivity, receptivity and NPRs in the mediobasal hypothalamus-preoptic area (MBH-POA) and pituitary (PIT) in females primed with 100% E<sub>2</sub>. An equivalent dose of Mox was without effect. ANI blocked the acute activation of feminine reproductive behavior by 1 mg of E<sub>2</sub>. In the absence of acute steroid administration, animals primed for 72 h with EB showed higher levels of reproductive behavior than animals primed with 100% E<sub>2</sub>. Likewise, as the dose of estrogen administered in the priming regimen was increased, the level of NPR in the MBH-POA and PIT increased in the absence of acute steroid (EB > 100% E<sub>2</sub> > 10% E<sub>2</sub>). These results suggest that the actions of E<sub>2</sub> via estrogen receptors are not by themselves sufficient to activate feminine reproductive behavior in the rat. The display of high levels of proceptivity and receptivity requires the subsequent activation of neural progestin receptors by P or by E<sub>2</sub>.

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          Author and article information

          Journal
          NEN
          Neuroendocrinology
          10.1159/issn.0028-3835
          Neuroendocrinology
          S. Karger AG
          0028-3835
          1423-0194
          1984
          1984
          28 March 2008
          : 39
          : 1
          : 25-30
          Affiliations
          Rockefeller University, New York, N.Y.; Department of Pharmacology, University of Pennsylvania Medical School, Philadelphia, Pa., USA
          Article
          123950 Neuroendocrinology 1984;39:25–30
          10.1159/000123950
          6540375
          © 1984 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: 6
          Categories
          Original Paper

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