期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2003
卷号：100
期号：5
页码：2969-2974
DOI：10.1073/pnas.0535708100
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The pulsatile secretion of gonadotropin-releasing hormone (GnRH) from normal and immortalized hypothalamic GnRH neurons is highly calcium-dependent and is stimulated by cAMP. It is also influenced by agonist activation of the endogenous GnRH receptor (GnRH-R), which couples to Gq/11 as indicated by release of membrane-bound q/11 subunits and increased inositol phosphate/Ca2+ signaling. Conversely, GnRH antagonists increase membrane-associated q/11 subunits and abolish pulsatile GnRH secretion. GnRH also stimulates cAMP production but at high concentrations has a pertussis toxin-sensitive inhibitory effect, indicative of receptor coupling to Gi. Coupling of the agonist-activated GnRH-R to both Gs and Gi proteins was demonstrated by the ability of nanomolar GnRH concentrations to reduce membrane-associated s and i3 levels and of higher concentrations to diminish i3 levels. Conversely, i3 was increased during GnRH antagonist and pertussis toxin treatment, with concomitant loss of pulsatile GnRH secretion. In cholera toxin-treated GnRH neurons, decreases in s immunoreactivity and increases in cAMP production paralleled the responses to nanomolar GnRH concentrations. Treatment with cholera toxin and 8-bromo-cAMP amplified episodic GnRH pulses but did not affect their frequency. These findings suggest that an agonist concentration-dependent switch in coupling of the GnRH-R between specific G proteins modulates neuronal Ca2+ signaling via Gs-cAMP stimulatory and Gi-cAMP inhibitory mechanisms. Activation of Gi may also inhibit GnRH neuronal function and episodic secretion by regulating membrane ion currents. This autocrine mechanism could serve as a timer to determine the frequency of pulsatile GnRH release by regulating Ca2+- and cAMP-dependent signaling and GnRH neuronal firing.
