Neuroendocrinology

Steroid Feedback on Reproductive Functions

Tamoxifen Induces Gonadotropin-Releasing Hormone Self-Priming through an Estrogen-Dependent Progesterone Receptor Expression in the Gonadotrope of the Rat

Bellido C.a · Martín de las Mulas J.b · Tena-Sempere M.a · Aguilar R.a · Alonso R.c · Sánchez-Criado J.E.a

Author affiliations

aDepartments of Cell Biology, Physiology and Immunology and bComparative Pathology, University of Córdoba, and cPhysiology, University of La Laguna, Spain

Keywords: TamoxifenSelective estrogen receptor modulatorsGonadotropinsGonadotropin releasing hormoneGonadal steroidsGonadal steroid receptorProlactinImmunocytochemistryMolecular neuroendocrinology

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Neuroendocrinology 2003;77:425–435
https://doi.org/10.1159/000071314

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Article / Publication Details

First-Page Preview
Abstract of Steroid Feedback on Reproductive Functions

Accepted: October 28, 2002
Published online: July 08, 2003
Issue release date: June 2003

Number of Print Pages: 11
Number of Figures: 6
Number of Tables: 2

ISSN: 0028-3835 (Print)
eISSN: 1423-0194 (Online)

For additional information: https://www.karger.com/NEN

Abstract

Tamoxifen (TX) is an antiestrogen with varying levels of antagonist/agonist activity on the reproductive axis of the rat. It has been reported that TX, in contrast to other selective estrogen receptor modulators (SERMs), increases the content of cytosolic estrogen receptors (ER) in the gonadotrope and induces gonadotropin releasing hormone (GnRH) self-priming in the absence of E. GnRH priming is believed to be a consequence of E-dependent progesterone receptor (PR) activation. The purpose of this study was to determine whether TX induces PR expression in the gonadotrope in an E-dependent manner, and whether the blockade of PR activation affects TX-dependent GnRH self-priming in ovariectomized (OVX) rats. Chronic OVX rats were injected (sc) over 3 days with 25 µg estradiol benzoate (EB), 3 mg TX, 0.5 mg RU58668, a ‘pure’ anti-E (aE), 2 mg RU38486, an anti-P at the receptor (aP), TX+aE and TX+aP. Controls were given 0.2 ml oil. While EB and TX increased mRNA for both PR A+B and PR B expression and the number and intensity of nuclei immunoreactive (IR) for PR in the gonadotrope, the aE and aP given alone had no effect on either PR mRNA levels or nuclear PR-IR. The aE reduced the effect of TX on PR expression (mRNA and nuclear IR) while the aP slightly reduced nuclear PR-IR only. In addition, pituitaries from each of the seven groups were incubated with: 10–8M E2, 10–7M TX, 10–8M aE, 10–8M aP, TX+aE, TX+aP or medium alone, respectively. Pituitaries were tested for GnRH self-priming (two pulses of 15 min 1 h apart) and the secretion of LH and PRL determined by specific RIAs. Pituitaries from rats treated with EB and incubated with E2 had increased basal and GnRH-stimulated luteinizing hormone (LH) and prolactin (PRL) secretion and GnRH self-priming. TX reduced basal and stimulated LH secretion, increased PRL secretion and induced a robust GnRH self-priming. All these effects of TX were blocked by the aE, while the aP blocked GnRH self-priming only. In conclusion, tamoxifen induced PR expression (mRNA and nuclear IR) in the gonadotrope in an E-dependent manner, while activation of these PR through intracellular signaling of GnRH induced GnRH self-priming.

© 2003 S. Karger AG, Basel



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Article / Publication Details

First-Page Preview
Abstract of Steroid Feedback on Reproductive Functions

Accepted: October 28, 2002
Published online: July 08, 2003
Issue release date: June 2003

Number of Print Pages: 11
Number of Figures: 6
Number of Tables: 2

ISSN: 0028-3835 (Print)
eISSN: 1423-0194 (Online)

For additional information: https://www.karger.com/NEN

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2003, Vol.77, No. 6

June 2003

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