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

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Farnworth, P. G. Articles by Burger, H. G. Search for Related Content PubMed PubMed Citation Articles by Farnworth, P. G. Articles by Burger, H. G.

The effects of 31 kDa bovine inhibin on the release of FSH and LH stimulated by gonadotrophin-releasing hormone (GnRH) or its agonist analogue buserelin have been studied using 5-day-old cultures of pituitary cells prepared from adult male Sprague–Dawley rats. Exposure of cultures to increasing concentrations of inhibin for 3 days before and during a 4-h stimulation with GnRH resulted in the progressive suppression of both basal and stimulated gonadotrophin release. At the highest inhibin concentrations FSH release was abolished (inhibin median inhibitory concentration (IC₅₀) = 0·15 U/ml) whereas LH release was suppressed by 75% (IC₅₀ = 0·93 U/ml). To correct for the reduced size of the FSH pool resulting from inhibin pretreatment, the amount of FSH or LH released by an agonist was expressed as a proportion of the total hormone available for release in each case. Following this adjustment, concentrations of inhibin producing maximal effects increased the GnRH median effective concentration for FSH release 4·1-fold and that for LH release 2·2-fold, with inhibin IC₅₀ values of 0·45 and 0·32 U/ml respectively. Inhibin also suppressed the maximum proportion of both FSH and LH that excess GnRH released in 4 h by 36%, with IC50 values of 0·53 and 0·76 U/ml respectively. These effects were not changed by reduction of the inhibin pretreatment period from 3 days to 1 day or by exclusion of inhibin during the stimulation period. After a 3-day pretreatment, inhibin inhibited gonadotrophin release by buserelin less effectively than that by GnRH, but the pattern of antagonism was the same.

The results show that purified bovine inhibin antagonizes the release of both FSH and LH stimulated by either GnRH or buserelin in vitro by reducing the apparent potency of GnRH agonists and by decreasing the proportion of total available gonadotrophin that can be released by an excess of GnRH agonist. Higher concentrations of inhibin are required for these common actions against stimulated release of FSH and LH than for the inhibition of FSH tonic synthesis/basal release, indicating one or more secondary sites of inhibin action in addition to its primary selective action to suppress the constitutive synthesis of FSH.

J. Endocr. (1988) 119, 233–241

This article has been cited by other articles:

				D. M. Robertson, G. E. Hale, D. Jolley, I. S. Fraser, C. L. Hughes, and H. G. Burger Interrelationships between Ovarian and Pituitary Hormones in Ovulatory Menstrual Cycles across Reproductive Age J. Clin. Endocrinol. Metab., January 1, 2009; 94(1): 138 - 144. [Abstract] [Full Text] [PDF]

				A. Gordon, J. C Garrido-Gracia, R. Aguilar, C. Bellido, J. A G. Velasco, Y. Millan, M. Tena-Sempere, J. Martin de las Mulas, and J. E Sanchez-Criado The ovary-mediated FSH attenuation of the LH surge in the rat involves a decreased gonadotroph progesterone receptor (PR) action but not PR expression J. Endocrinol., March 1, 2008; 196(3): 583 - 592. [Abstract] [Full Text] [PDF]