title: Rapid Glucocorticoid Feedback Inhibition of ACTH Secretion Involves Ligand-Dependent Membrane Association of Glucocorticoid Receptors.
abstract: The hypothesis that rapid glucocorticoid inhibition of pituitary ACTH secretion mediates a feedforward/feedback mechanism responsible for the hourly glucocorticoid pulsatility was tested in cultured pituitary cells. Perifusion with 30 pM CRH caused sustained the elevation of ACTH secretion. Superimposed corticosterone pulses inhibited CRH-stimulated ACTH release, depending on prior glucocorticoid clearance. When CRH perifusion started after 2 hours of glucocorticoid-free medium, corticosterone levels in the stress range (1 μM) caused a delayed (25 min) and prolonged inhibition of CRH-stimulated ACTH secretion, up to 60 minutes after corticosterone withdrawal. In contrast, after 6 hours of glucocorticoid-free medium, basal corticosterone levels inhibited CRH-stimulated ACTH within 5 minutes, after rapid recovery 5 minutes after corticosterone withdrawal. The latter effect was insensitive to actinomycin D but was prevented by the glucocorticoid receptor antagonist, RU486, suggesting nongenomic effects of the classical glucocorticoid receptor. In hypothalamic-derived 4B cells, 10 nM corticosterone increased immunoreactive glucocorticoid receptor content in membrane fractions, with association and clearance rates paralleling the effects on ACTH secretion from corticotrophs. Corticosterone did not affect CRH-stimulated calcium influx, but in AtT-20 cells, it had biphasic effects on CRH-stimulated Src phosphorylation, with early inhibition and late stimulation, suggesting a role for Src phosphorylation on the rapid glucocorticoid feedback. The data suggest that the nongenomic/membrane effects of classical GR mediate rapid and reversible glucocorticoid feedback inhibition at the pituitary corticotrophs downstream of calcium influx. The sensitivity and kinetics of these effects is consistent with the hypothesis that pituitary glucocorticoid feedback is part of the mechanism for adrenocortical ultradian pulse generation.
authors.affiliation: Sections on Endocrine Physiology (Q.D., D.R., L.T., G.A.) and Cellular Signaling (M.T., S.S.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; College of Animal Sciences (Q.D.), Jilin University, Chang Chun 130021, China; and Department of Molecular and Integrative Physiology (M.J.L.), University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Deng
authors.affiliation: Sections on Endocrine Physiology (Q.D., D.R., L.T., G.A.) and Cellular Signaling (M.T., S.S.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; College of Animal Sciences (Q.D.), Jilin University, Chang Chun 130021, China; and Department of Molecular and Integrative Physiology (M.J.L.), University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Denise
authors.initials: D
authors.lastname: Riquelme
authors.affiliation: Sections on Endocrine Physiology (Q.D., D.R., L.T., G.A.) and Cellular Signaling (M.T., S.S.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; College of Animal Sciences (Q.D.), Jilin University, Chang Chun 130021, China; and Department of Molecular and Integrative Physiology (M.J.L.), University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Loc
authors.initials: L
authors.lastname: Trinh
authors.affiliation: Sections on Endocrine Physiology (Q.D., D.R., L.T., G.A.) and Cellular Signaling (M.T., S.S.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; College of Animal Sciences (Q.D.), Jilin University, Chang Chun 130021, China; and Department of Molecular and Integrative Physiology (M.J.L.), University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Malcolm J
authors.initials: MJ
authors.lastname: Low
authors.affiliation: Sections on Endocrine Physiology (Q.D., D.R., L.T., G.A.) and Cellular Signaling (M.T., S.S.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; College of Animal Sciences (Q.D.), Jilin University, Chang Chun 130021, China; and Department of Molecular and Integrative Physiology (M.J.L.), University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Melanija
authors.initials: M
authors.lastname: Tomić
authors.affiliation: Sections on Endocrine Physiology (Q.D., D.R., L.T., G.A.) and Cellular Signaling (M.T., S.S.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; College of Animal Sciences (Q.D.), Jilin University, Chang Chun 130021, China; and Department of Molecular and Integrative Physiology (M.J.L.), University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Stanko
authors.initials: S
authors.lastname: Stojilkovic
authors.affiliation: Sections on Endocrine Physiology (Q.D., D.R., L.T., G.A.) and Cellular Signaling (M.T., S.S.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892; College of Animal Sciences (Q.D.), Jilin University, Chang Chun 130021, China; and Department of Molecular and Integrative Physiology (M.J.L.), University of Michigan Medical School, Ann Arbor, Michigan 48109.
authors.forename: Greti
authors.initials: G
authors.lastname: Aguilera
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D020013:Calcium Signaling; D002478:Cells, Cultured; D003345:Corticosterone / Q000008:administration & dosage*; D052680:Corticotrophs / Q000378:metabolism*; D003346:Corticotropin-Releasing Hormone; D025461:Feedback, Physiological; D005260:Female; D005938:Glucocorticoids / Q000378:metabolism*; D008024:Ligands; D008297:Male; D010766:Phosphorylation; D017207:Rats, Sprague-Dawley; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D005938:Glucocorticoids; D008024:Ligands; D011965:Receptors, Glucocorticoid; D000324:Adrenocorticotropic Hormone; D003346:Corticotropin-Releasing Hormone; D019061:src-Family Kinases; D003345:Corticosterone