Estradiol-17β inhibits gonadotropin-releasing hormone-induced Ca 2 in gonadotropes to regulate negative feedback on luteinizing hormone release

Abstract

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 alo..