Krsmanovic L Z, Mores N, Navarro C E, Saeed S A, Arora K K, Catt K J
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Endocrinology. 1998 Oct;139(10):4037-43. doi: 10.1210/endo.139.10.6267.
Agonist activation of cholinergic receptors expressed in perifused hypothalamic and immortalized GnRH-producing (GT1-7) cells induced prominent peaks in GnRH release, each followed by a rapid decrease, a transient plateau, and a decline to below basal levels. The complex profile of GnRH release suggested that acetylcholine (ACh) acts through different cholinergic receptor subtypes to exert stimulatory and inhibitory effects on GnRH release. Whereas activation of nicotinic receptors caused a transient increase in GnRH release, activation of muscarinic receptors inhibited basal GnRH release. Nanomolar concentrations of ACh caused dose-dependent inhibition of cAMP production that was prevented by pertussis toxin (PTX), consistent with the activation of a plasma-membrane Gi protein. Micromolar concentrations of ACh also caused an increase in phosphoinositide hydrolysis that was inhibited by the M1 receptor antagonist, pirenzepine. In ACh-treated cells, immunoblot analysis revealed that membrane-associated G(alpha q/11) immunoreactivity was decreased after 5 min but was restored at later times. In contrast, immunoreactive G(alpha i3) was decreased for up to 120 min after ACh treatment. The agonist-induced changes in G protein alpha-subunits liberated during activation of muscarinic receptors were correlated with regulation of their respective transduction pathways. These results indicate that ACh modulates GnRH release from hypothalamic neurons through both M1 and M2 muscarinic receptors. These receptor subtypes are coupled to Gq and Gi proteins that respectively influence the activities of PLC and adenylyl cyclase/ion channels, with consequent effects on neurosecretion.
在下丘脑灌流细胞和永生化促性腺激素释放激素（GnRH）分泌细胞（GT1-7）中表达的胆碱能受体的激动剂激活诱导了GnRH释放的显著峰值，随后迅速下降，出现短暂平台期，然后降至基础水平以下。GnRH释放的复杂模式表明，乙酰胆碱（ACh）通过不同的胆碱能受体亚型发挥作用，对GnRH释放产生刺激和抑制作用。烟碱样受体的激活导致GnRH释放短暂增加，而毒蕈碱样受体的激活则抑制基础GnRH释放。纳摩尔浓度的ACh导致cAMP生成呈剂量依赖性抑制，百日咳毒素（PTX）可阻止这种抑制，这与质膜Gi蛋白的激活一致。微摩尔浓度的ACh还导致磷酸肌醇水解增加，M1受体拮抗剂哌仑西平可抑制这种增加。在ACh处理的细胞中，免疫印迹分析显示，膜相关G（αq/11）免疫反应性在5分钟后降低，但在随后的时间恢复。相比之下，ACh处理后长达120分钟，免疫反应性G（αi3）降低。毒蕈碱样受体激活过程中释放的G蛋白α亚基的激动剂诱导变化与其各自转导途径的调节相关。这些结果表明，ACh通过M1和M2毒蕈碱样受体调节下丘脑神经元GnRH的释放。这些受体亚型分别与Gq和Gi蛋白偶联，影响磷脂酶C和腺苷酸环化酶/离子通道的活性，从而影响神经分泌。
