title: Role of phosphodiesterases in the regulation of gonadotropin- releasing hormone secretion in GT1 cells.
abstract: Increases in the level of cAMP stimulate the secretion of GnRH from GT1 GnRH neuronal cells. We hypothesized that cyclic nucleotide phosphodiesterases (PDEs), the enzymes that hydrolyze cAMP, may constitute a negative feedback signaling mechanism for GnRH regulation by decreasing the level of cAMP. GT1 cells were shown to express three PDEs by RT-PCR analysis: the cAMP-specific PDE4B and PDE4D and the calmodulin-dependent PDE1B. A splice variant of PDE4D, PDE4D3, which is activated when phosphorylated by cAMP-dependent protein kinase (PKA), was identified in GT1 cells by Western analysis. Consistent with PDEs negatively regulating GnRH secretion, treatment with the nonselective PDE inhibitor, IBMX, stimulated GnRH secretion 137% in 30-min static cultures. Furthermore, treatment with the PDE4-specific inhibitors Rolipram and RS-25344 increased GnRH secretion 48 and 125%, while treatment with the PDE1-specific inhibitor 8-MeoM-IBMX only caused a modest increase of 28%. In perifusion studies a rapid multi-fold stimulation of GnRH secretion was observed following treatment with IBMX, Rolipram or RS-25344. In conclusion, the level of PDE activity appears to be an important negative feedback signal for GnRH secretion. We hypothesize that activation of PDE4D3 by PKA may constitute a negative feedback signaling pathway which participates in the regulation of cAMP levels.
authors.affiliation: Department of Obstetrics, Gynecology and Reproductive Sciences, University of California School of Medicine, San Francisco, Calif., 94143-0556, USA.
authors.forename: H
authors.initials: H
authors.lastname: Sakakibara
authors.forename: M
authors.initials: M
authors.lastname: Conti
authors.forename: R I
authors.initials: RI
authors.lastname: Weiner
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010477:Perfusion; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D010726:Phosphodiesterase Inhibitors; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP; D010727:Phosphoric Diester Hydrolases