Chang J P, Garofalo R, Neumann C M
Department of Biological Sciences, University of Alberta, Edmonton, Canada.
Gen Comp Endocrinol. 1995 Dec;100(3):339-54. doi: 10.1006/gcen.1995.1165.
The signal transduction mechanisms mediating the acute actions of salmon gonadotropin (GTH)-releasing hormone (sGnRH) and chicken GnRH-II (cGnRH-II) on GTH release from goldfish pituitary cells were compared. In cell column perifusion experiments, treatment with inhibitors of phospholipase A2 (50 microM quinacrine or 50 microM bromophenacylbromide) or the lipoxygenase enzyme (50 microM nordihydroguaiaretic acid) reduced the GTH response to 100 nM sGnRH, but not the response to 100 nM cGnRH-II. These results suggest that AA mobilization through phospholipase A2 and the subsequent metabolism of AA through the lipoxygenase pathway are involved in rapid sGnRH-induced GTH secretion, but not in acute cGnRH-II action. Consistent with the idea that calcium entry through voltage-sensitive calcium channels is involved in acute GnRH action, perfusion with 1 microM verapamil, a voltage-sensitive calcium channel inhibitor, reduced both 100 nM sGnRH- and 100 nM cGnRH-II-induced GTH secretion. However, the response to cGnRH-II was decreased to a greater extent compared to sGnRH-elicited release, suggesting a greater dependence on extracellular calcium entry for acute cGnRH-II-stimulated GTH secretion. The metabolism of inositol phosphates (InsPs) following acute sGnRH and cGnRH-II administration was also investigated by monitoring the levels of [3H]InsPs in [3H]inositol-prelabeled goldfish pituitary cells. Incubation with 100 nM sGnRH increased [3H]InsP1 by 5 min and [3H]InsP2, [3H]InsP3, and other higher [3H]InsPs by 10 min. In contrast, following 10 min of stimulation by 100 nM cGnRH-II, only [3H]InsP2 levels were elevated, suggesting that cGnRH-II may activate a different set of enzymes in the phosphoinositide metabolic pathways compared to sGnRH. The lack of an InsP3 response may also reflect the relative ineffectiveness of cGnRH-II to mobilize calcium from intracellular stores. Taken together, these results strongly indicate that the mechanisms mediating rapid sGnRH-induced and cGnRH-II-elicited GTH responses are different as in the case for prolonged GnRH action.
比较了介导鲑鱼促性腺激素（GTH）释放激素（sGnRH）和鸡GnRH-II（cGnRH-II）对金鱼垂体细胞释放GTH的急性作用的信号转导机制。在细胞柱灌流实验中，用磷脂酶A2抑制剂（50μM奎纳克林或50μM溴苯甲酰溴）或脂氧合酶（50μM去甲二氢愈创木酸）处理可降低对100 nM sGnRH的GTH反应，但不影响对100 nM cGnRH-II的反应。这些结果表明，通过磷脂酶A2动员花生四烯酸（AA）以及随后通过脂氧合酶途径对AA的代谢参与了sGnRH诱导的快速GTH分泌，但不参与cGnRH-II的急性作用。与电压敏感性钙通道的钙内流参与急性GnRH作用的观点一致，用1μM维拉帕米（一种电压敏感性钙通道抑制剂）灌流可降低100 nM sGnRH和100 nM cGnRH-II诱导的GTH分泌。然而，与sGnRH引起的释放相比，对cGnRH-II的反应下降幅度更大，表明急性cGnRH-II刺激的GTH分泌对细胞外钙内流的依赖性更大。通过监测[3H]肌醇预标记的金鱼垂体细胞中[3H]肌醇磷酸（InsPs）的水平，还研究了急性给予sGnRH和cGnRH-II后肌醇磷酸的代谢情况。用100 nM sGnRH孵育5分钟可使[3H]InsP1增加，10分钟可使[3H]InsP2、[3H]InsP3和其他更高的[3H]InsPs增加。相反，在100 nM cGnRH-II刺激10分钟后，仅[3H]InsP2水平升高，这表明与sGnRH相比，cGnRH-II可能激活磷脂酰肌醇代谢途径中的一组不同的酶。InsP3反应的缺乏也可能反映了cGnRH-II从细胞内储存中动员钙的相对无效性。综上所述，这些结果强烈表明，介导sGnRH诱导的快速和cGnRH-II引起的GTH反应的机制与GnRH的长期作用情况不同。
