Physiological role of gonadotropin-releasing hormone (LH-RH) on ovarian function ; phosphoinositide metabolism in granulosa cells.

在大鼠颗粒细胞中，促黄体生成素以剂量依赖的方式诱导三磷酸肌醇(IP&lt；D23&Gt；D2)的形成。促卵泡激素(FSH)诱导的IP_3形成与促黄体生成素(LH-RH)同时减少。这两种现象的一半最大效应出现在约10^&lt；-9&gt；MLh-RH。刺激IP_3形成和抑制雌激素产生的镜像数据可能表明，颗粒细胞中受刺激的磷脂酰肌醇的降解与抑制类固醇的合成紧密耦合。芳香酶活性被认为是颗粒细胞中雌激素形成的限速步骤，它被测量为雄烯二酮到雌酮的细胞转化率。FSH对芳香酶活性有明显的抑制作用，抑制作用滞后时间为32h。在培养32h，FSH对雌酮的产生影响不大，此后雌酮的产生速率逐渐增加。与黄体生成素释放激素DECRE…同时孵育使FSH诱导的雌酮产量降至对照水平。促性腺激素释放激素刺激雌酮产生的半数有效浓度(EC_(50))在加或不加促黄体生成素的细胞中几乎相同，提示为非竞争性抑制方式。用蛋白激酶C激活剂测定促黄体生成素释放激素。蛋白激酶C的激活可能会抑制FSH诱导的芳香酶诱导，然后利用竞争性拮抗剂ANTID来确定LH-RH是否需要持久的受体占据才能在颗粒细胞上发挥这种作用，或者LH-RH是否通过首先和短暂的刺激而继续发挥作用。促黄体生成素能刺激磷脂酰肌醇(PtdIns)掺入磷脂酰肌醇(PtdIns)，这种作用可通过安替取代先前结合的促黄体生成素受体而终止，并可通过用促黄体生成素重新结合受体而重新启动。Antie可迅速阻止Lh-RH刺激的Ptdlns磷酸化。在LH-RH的抗FSH作用中，也观察到了同样的作用。FSH启动的芳香酶活性可被LHRH猝灭，而当LHRH被安多德从其受体上移除时，芳香酶活性又重新启动。这两种反应与LHRH受体的占位有关，为促进Ptdlns周转和抑制芳香酶活性的紧密耦合提供了证据。这些数据表明芳香酶的激活需要持续的激活。综上所述，卵巢中的促黄体生成素或促黄体生成素样激素，除来自垂体外，还可能以自分泌或旁分泌的方式参与卵巢类固醇激素的合成调控。较少

In rat granulosa cells, LH-RH induced inositol trisphosphate (IP<D23>D2) formation in a dose-dependent manner. Estrogen production in response to follicular-stimulating hormone (FSH) was reduced by LH-RH in parallel with LH-RH-stimulated IP_3 formation. Half maximal effects of both phenomena occurred at about 10^<-9> M LH-RH. The mirror-image data of stimulation of IP_3 formation and inhibition of estrogen production might suggest tight coupling of stimulated phosphoinositide degradation to suppressed steroidogenesis in the granulosa cells. The aromatase activity, considered as rate-limiting step of estrogen formation in granulosa cells, was measured as the rate of cellular conversion of androstenedione to estrone. FSH exerted a markedly inhibitory effect on the aromatase activity with a lag time of 32h. There were slight effects of FSH on estrone production for the fust 32h, and, thereafter, the rate of estrone production increased progressively. Concurrent incubation with LH-RH decre … More ased the FSH-induced estrone production to the control level. The 50% effective concentration (EC_<50>) for FSH stimulation of estrone production was almost equal in the cells incubated with or without LH-RH, suggesting the noncompetitive inhibitory fashion. The identical data of LH-RH was obtained by protein kinase C activators. Protein kinase C activation might inhibit FSH-induced aromatase induction.It was then undertaken to determine whether persistent receptor occupancy was necessary for LH-RH to exert such actions on granulosa cells, or whether LH-RH actions were continued by a first and transient stimulation by LH-RH, using a competitive antagonist, antide. LH-RH stimulated[ ^<32>Plphosphate incorporation into phosphatidylinositol (PtdIns), which could be terminated by displacement of previously bound LH-RH from its receptor by antide and restarted by reoccupying the receptors with LH-RH. Antide could rapidly prevent LH-RH-stimulated Ptdlns phosphorylation whenever it was added to incubations. An identical effect of antide was observed also in the anti-FSH action of LH-RH. The aromatase activity initiated by FSH was quenched by LH-RH and restarted at a time when LH-RH was removed from its receptor by antide. These two responses associated with the occupancy of LH-RH receptor provide the evidence in favor of a tight coupling of stimulated Ptdlns turnover to suppression of aromatase activation. These data of required continued activation of aromatase activation. Taken together these data of requirement of continued occupancy of receptor for LH-RH to exert its action, LH-RH or LH-RH-like hormone in ovaries, in addition to from pituitary, could participate in the control of steroidogenesis in the ovary in an autocrine or a paracrine manner. Less