Rapid in vivo effects of estradiol-17β in ovine pituitary gonadotropes are displayed by phosphorylation of extracellularly regulated kinase, serine/threonine kinase, and 3′,5′-cyclic adenosine 5′-monophosphate-responsive element-binding protein

Abstract

We have determined the time course of phosphorylation of MAPK/ERK, cAMP-responsive element-binding protein (CREB), and serine/threonine kinase (Akt) in ovine pituitary gonadotropes after in vivo injection (iv) of either 25 μg estradiol-17β (E17β) or vehicle. In ovariectomized ewes, E17β increased the number of gonadotropes expressing phosphorylated (p)ERK-1/2 and pCREB immunoreactivity (-IR) within 90 min, as assessed by immunohistochemistry. By Western blot, we also showed that pERK-1/2, pCREB, and pAkt (ser 473) proteins were up-regulated by E17β. In ovariectomized, hypothalamo-pituitary-disconnected animals, gonadotrope function was restored with hourly GnRH pulses (iv), and E17β injection (iv) reduced LH response within 1 h. Immunohistochemistry showed that E17β increased pERK-1/2-IR in gonadotropes within 15 min and peak response at 60 min. The number of cells immunoreactive for pCREB was greater in E17β-treated animals than in vehicle-injected controls at 60 and 90 min. Western blot revealed a pERK-1/2 response within 15 min and pCREB response at 30 min. Up-regulation of pAkt occurred within 60 min of E17β treatment. Thus, rapid effects of E17β on gonadotropes involve phosphorylation of second messenger proteins with a time course that may relate to the rapid negative feedback effect to reduce responsiveness to GnRH. Copyright © 2007 by The Endocrine Society.