title: Receptor phosphorylation mediates estradiol reduction of alpha2-adrenoceptor coupling to G protein in the hypothalamus of female rats.
abstract: Estrogen increases evoked norepinephrine release in the hypothalamus of female rodents, in part by reducing the ability of alpha2-adrenoceptors to act as negative feed-back inhibitors of norepinephrine release. Estrogen enhancement of norepinephrine release in the hypothalamus correlates with decreased coupling of the alpha2-adrenoceptor to G protein. To determine the mechanism by which estrogen uncouples alpha2-adrenoceptors from G protein, we tested the hypothesis that estrogen increases alpha2-adrenoceptor phosphorylation. Short-term activation of endogenous serine/threonine phosphatases with protamine or treatment with exogenous phosphatase restored alpha2-adrenoceptor coupling to G protein to control levels in hypothalami from estrogen-exposed female rats. Additional experiments examined whether estrogen alters G protein-coupled receptor kinase expression or activity or serine/threonine phosphatase activity. These proteins are involved in G protein-coupled receptor phosphorylation, internalization, and recycling. Estrogen exposure reduced G protein-coupled receptor kinase mRNA, protein, and activity in the hypothalamus. Furthermore, estrogen treatment reduced serine/threonine phosphatase activity in the hypothalamus. Analysis of ligand binding in subcellular fractions demonstrated that estrogen decreases the fraction of internalized alpha2-adrenoceptors in the hypothalamus.Therefore, estrogen promotes norepinephrine release in the hypothalamus by stabilizing alpha2-adrenoceptor phosphorylation, uncoupling the receptor from G protein. Estrogen may stabilize alpha2-adrenoceptor phosphorylation by inhibiting receptor internalization and dephosphorylation.
authors.affiliation: Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Ansonoff
authors.forename: A M
authors.initials: AM
authors.lastname: Etgen
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D007031:Hypothalamus / Q000378:metabolism*; D019329:Idazoxan / Q000031:analogs & derivatives / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D010052:Ovariectomy; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism*; D014316:Tritium; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D014316:Tritium; D004958:Estradiol; C058525:2-methoxyidazoxan; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D010749:Phosphoprotein Phosphatases; D019204:GTP-Binding Proteins; D009638:Norepinephrine; D019329:Idazoxan