Rapid in vivo effects of estradiol-17beta 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.
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 mug estradiol-17beta (E17beta) or vehicle. In ovariectomized ewes, E17beta 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 E17beta. In ovariectomized, hypothalamo-pituitary-disconnected animals, gonadotrope function was restored with hourly GnRH pulses (iv), and E17beta injection (iv) reduced LH response within 1 h. Immunohistochemistry showed that E17beta 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 E17beta-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 E17beta treatment. Thus, rapid effects of E17beta 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.
Iqbal
Javed
J
Department of Physiology, Monash University, Clayton, Victoria 3880, Australia.
Latchoumanin
Olivier
O
Clarke
Iain J
IJ
D000818:Animals; D015153:Blotting, Western; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology; D007150:Immunohistochemistry; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D010052:Ovariectomy; D010766:Phosphorylation / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011863:Radioimmunoassay; D012756:Sheep