Dopaminergic regulation of the GT1 gonadotropin-releasing hormone (GnRH) neuronal cell lines: stimulation of GnRH release via D1-receptors positively coupled to adenylate cyclase.

The release of GnRH evoked by dopamine (DA) was studied in the GT1 GnRH neuronal cell lines. Superfusion of GT1-1 cells with DA or the D1-dopaminergic agonist SKF 38393, but not with the D2-dopaminergic agonist bromocriptine, increased 2-fold the amplitude of the spontaneous GnRH pulses. Treatment with DA for 30 min also stimulated GnRH release from static cultures of GT1-7 cells. This effect was mimicked by the selective D1-dopaminergic agonist SKF 38393 and blocked by the D1-dopaminergic antagonist SCH 23390. However, the D2-dopaminergic agonist bromocriptine had no effect, and the stimulation of GnRH release by DA was not blocked by the D2-dopaminergic antagonist spiroperidol. In parallel to the stimulation of GnRH release, DA also rapidly increased (first observed at 120 sec) in a dose-dependent fashion, the intracellular concentration of cAMP in isobutylmethylxanthine-pretreated GT1-7 cells. The pharmacological profile of the increase in cAMP was identical to that for GnRH release. The cAMP responses to DA and norepinephrine were lost after long term treatment with SKF 38393, i.e. heterologous desensitization. GT1 cells also express the mRNA for the dopamine- and cAMP-regulated phospho-protein (mol wt, 32,000; DARPP-32) only seen in cells expressing DA D1-receptors. These results demonstrate a direct stimulatory effect of DA on GnRH release via DA D1-receptors positively coupled to adenylate cyclase in GnRH neuronal cell lines.