This Article Full Text Full Text (PDF) Supplemental Data 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 Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Google Scholar Articles by Iqbal, J. Articles by Clarke, I. J. PubMed PubMed Citation Articles by Iqbal, J. Articles by Clarke, I. J.

Estradiol-17β Inhibits Gonadotropin-Releasing Hormone-Induced Ca²⁺ in Gonadotropes to Regulate Negative Feedback on Luteinizing Hormone Release

Department of Physiology, Monash University, Clayton, Victoria 3800, Australia

Address all correspondence and requests for reprints to: Professor Iain Clarke, Department of Physiology, P.O. Box 13F, Monash University, Clayton, Victoria 3800, Australia. E-mail: iain.clarke{at}med.monash.edu.au.

In pituitary gonadotropes, estrogens have biphasic actions to cause an initial negative feedback followed by a positive feedback on LH secretion, but the mechanisms involved are not clearly understood. To investigate the feedback effects of estrogen, we used mixed ovine pituitary cell cultures (48–72 h), which were treated with 10^–9 M estradiol-17β (E₂) or vehicle followed by a pulse of 10^–9 M GnRH. Medium was collected for LH assay and cells extracted to determine activation of MAPK (phosphorylated ERK-1/2). E₂ treatment for 5 min reduced GnRH-induced LH release and caused phosphorylation of ERK-1/2. E₂ alone also caused phosphorylation of ERK-1/2, similar to the response evoked by GnRH alone. GnRH increased cytoplasmic intracellular free calcium concentration ([Ca²⁺]_i) and this was abolished by 2 min pretreatment with E₂ or E-bovine serum albumen conjugate. Blockade of Ca²⁺ channels with nifedipine had no effect on the initial peak of GnRH-induced increase in [Ca²⁺]_i but reduced its duration by 27 ± 6%. Depletion of intracellular Ca²⁺ stores with thapsigargin prevented GnRH-induced increase in [Ca²⁺]_i. Thapsigargin (10^–7 M) or nifedipine (10^–5 M) pretreatment (15 min) of cells lowered GnRH-induced LH secretion by 30 ± 6 and 50% ± 4%, respectively. We conclude that inhibition of the GnRH-induced increase in [Ca²⁺]_i in gonadotropes by E₂ is a likely mechanism for the negative feedback effect of E₂ on LH secretion involving a rapid nongenomic effect of E₂. Activation of the MAPK pathway by E₂ may be the mechanism for the time-delayed positive feedback effect on LH secretion at the level of the gonadotrope.

This article has been cited by other articles:

				I. P. Sari, A. Rao, J. T. Smith, A. J. Tilbrook, and I. J. Clarke Effect of RF-Amide-Related Peptide-3 on Luteinizing Hormone and Follicle-Stimulating Hormone Synthesis and Secretion in Ovine Pituitary Gonadotropes Endocrinology, December 1, 2009; 150(12): 5549 - 5556. [Abstract] [Full Text] [PDF]