Beta 1-adrenergic regulation of the GT1 gonadotropin-releasing hormone (GnRH) neuronal cell lines: stimulation of GnRH release via receptors positively coupled to adenylate cyclase.

ABSTRACT

The release of GnRH evoked by norepinephrine (NE) was studied in GT1 GnRH neuronal cell lines in superfusion and static cultures. GnRH release from static cultured GT1-7 cells was stimulated by NE in a dose-dependent fashion. This effect was mimicked by the nonsubtype-selective beta-adrenergic agonist isoproterenol and blocked by the beta-adrenergic antagonist propranolol and the beta 1-adrenergic subtype-specific antagonist CGP 20712A. However, the stimulation of GnRH release by NE was not affected by the beta 2-, alpha-, alpha 1-, or alpha 2-adrenergic antagonists ICI 118.551, phentolamine, prazosin, or yohimbine, respectively. Superfusion of GT1-1 cells with NE for 60-100 min resulted in rapid and sustained increases in GnRH secretion. The NE-stimulated GnRH release showed a higher amplitude and longer duration than the spontaneous GnRH pulses characteristic of GT1-1 cells. In parallel to the stimulation of GnRH release, NE also rapidly increased (first observed at 60 sec) the intracellular concentration of cAMP in isobutylmethylxanthine-pretreated GT1-1 and GT1-7 cells in a dose-dependent fashion. The stimulation of intracellular cAMP concentration was also mimicked by isoproterenol and blocked by propranolol and CGP 20712A. In addition, GT1 cells express beta 1- but not beta 2-adrenergic receptor mRNA, as probed by Northern blot analysis. These results demonstrate a direct stimulatory effect of NE on GnRH neurons. The pharmacological evidence and the mRNA analysis are consistent with NE acting through a beta 1-adrenergic receptor positively coupled to adenylate cyclase.