HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal My Folders Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Molter-Gérard, C. Articles by Taragnat, C. Search for Related Content PubMed PubMed Citation Articles by Molter-Gérard, C. Articles by Taragnat, C. Agricola Articles by Molter-Gérard, C. Articles by Taragnat, C.

Dynamic Changes in the Gonadotrope Cell Subpopulations During an Estradiol-Induced Surge in the Ewe¹

^a Institut National de la Recherche Agronomique/Unité de Recherche Associée CNRS 1291, Station de Physiologie de la Reproduction des Mammifères Domestiques, 37380 Nouzilly, France

Whether estradiol targets a subpopulation of gonadotrope cells was investigated in this study. Ovariectomized ewes (OVX) or OVX ewes immunized against GnRH and treated with hourly pulses of GnRH analogue (OVX-IMG) were killed at 6, 12, 16, and 24 h after administration of 50 µg of 17ß-estradiol (E₂). Control ewes received no E₂ treatment. In OVX or OVX-IMG ewes killed 6 h after E₂ injection, a decrease in gonadotropin plasma levels was observed compared with non-E₂-treated ewes. In contrast, a surge in gonadotropin plasma concentrations occurred in ewes killed 16 h after injection. The percentage of total immunoreactive gonadotrope cells among the pituitary cells was lower in E₂-treated ewes compared with nontreated animals. The proportion of monohormonal LH cells was constant throughout the experiment, except at the surge peak, where it was enhanced. In the OVX ewes, the proportion of bihormonal LH/FSH cells was lower in the E₂-treated ewes compared to the nontreated ewes (P < 0.001), with a more pronounced decrease 16 h after E₂ injection. A slight increase occurred 12 h after E₂ injection compared with 6 h after injection (P < 0.05). A similar pattern was observed in the OVX-IMG ewes, except at 12 h after E₂ injection, when no increase occurred. In both OVX and OVX-IMG ewes, injection of E₂ decreased FSHß mRNA expression but did not alter the relative levels of LHß mRNA. These data suggest that the negative feedback of E₂ on LH and FSH secretion mainly targets the bihormonal cells and occurs, at least in part, directly at the pituitary level. During the gonadotropin surge, the sustained FSH release from the bihormonal cells would induce a switch from bihormonal cells to monohormonal LH cells by depleting these cells of FSH.

First decision: 8 September 1999.

¹ Supported by a grant from the Région Centre.

² Correspondence: Catherine Taragnat, Institut National de la Recherche Agronomique, Station de Physiologie de la Reproduction des Mammifères Domestiques, 37380 Nouzilly, France. FAX: 33 247427743;taragnat{at}tours.inra.fr

This article has been cited by other articles:

				M-O Faure, L Nicol, S Fabre, J Fontaine, N Mohoric, A McNeilly, and C Taragnat BMP-4 inhibits follicle-stimulating hormone secretion in ewe pituitary J. Endocrinol., July 1, 2005; 186(1): 109 - 121. [Abstract] [Full Text] [PDF]

				C. Xu, X.-Z. Xu, C. S. Nunemaker, and S. M. Moenter Dose-Dependent Switch in Response of Gonadotropin-Releasing Hormone (GnRH) Neurons to GnRH Mediated through the Type I GnRH Receptor Endocrinology, February 1, 2004; 145(2): 728 - 735. [Abstract] [Full Text] [PDF]

				D. Meeran, H. F. Urbanski, S. J. Gregory, J. Townsend, and D. J. Tortonese Developmental Changes in the Hormonal Identity of Gonadotroph Cells in the Rhesus Monkey Pituitary Gland J. Clin. Endocrinol. Metab., June 1, 2003; 88(6): 2934 - 2942. [Abstract] [Full Text] [PDF]