Roudbaraki M M, Drouhault R, Bacquart T, Vacher P
Laboratoire de Neurophysiologie, Unité de Recherche Associée au Centre National de la Recherche Scientifique, Université de Bordeaux France.
Neuroendocrinology. 1996 Mar;63(3):244-56. doi: 10.1159/000126964.
Arachidonic acid (AA) has been implicated in signaling actions in several cell types including endocrine cells. In the present study, we investigated the effect of exogenous AA on GH release from dispersed pituitary cells and tried to elucidate the mechanism involved in this process. We show that AA stimulates GH release in a dose- and extracellular calcium-dependent manner. The effects of AA on cytosolic calcium concentration ([Ca2+]i) were studied using dual-emission microspectrofluorimetry in identified somatotropes. AA (1 microM) induced an increase in intracellular calcium concentration ([Ca2+]i) by stimulating Ca2+ influx through dihydropyridine-sensitive, voltage-dependent calcium channels. In these cells, the effects of AA were only reduced by the inhibition of protein kinase C (PKC) activity, suggesting that the fatty acid may act by both PKC-dependent and PKC-independent pathways. In order to determine whether AA metabolites were involved in the effects attributed to AA, and, if so, which ones, we inhibited the three arachidonate metabolic pathways: cyclo-oxygenase by indomethacin (50 microM), lipoxygenase by nordihydroguaiaretic acid (NGDA, 50 microM), and epoxygenase by 5,8,11, 14-eicosatetraynoic acid (ETYA, 10 microM). NGDA and ETYA reduced the effects of AA on GH release (50 and 74%, respectively) and inhibited the [Ca2+]i response, whereas indomethacin slightly potentiated both AA-induced GH release and [Ca2+]i increase. As these results suggested that lipoxygenase metabolites may be responsible for AA-induced Ca2+ influx and GH release, we tested the effects of 5-, 12- and 15-hydroperoxyeicosatetraenoic acids (5-, 12- and 15-HpETE) on [Ca2+]i and GH release. They all stimulated calcium influx and GH release in a dose-dependent manner, 12-HpETE being more potent than 5- and 15-HpETE. We conclude that lipoxygenase metabolites of arachidonic acid, particularly 12-HpETE, may be involved in the GH secretion mechanism, probably by facilitating Ca2+ influx via L-type Ca2+ channels.
花生四烯酸（AA）已被证实参与包括内分泌细胞在内的多种细胞类型的信号传导作用。在本研究中，我们探究了外源性AA对分散的垂体细胞释放生长激素（GH）的影响，并试图阐明这一过程涉及的机制。我们发现，AA以剂量和细胞外钙依赖的方式刺激GH释放。利用双发射显微荧光光谱法在已鉴定的生长激素分泌细胞中研究了AA对细胞质钙浓度（[Ca2+]i）的影响。AA（1微摩尔）通过刺激钙经二氢吡啶敏感的电压依赖性钙通道内流，诱导细胞内钙浓度（[Ca2+]i）升高。在这些细胞中，只有抑制蛋白激酶C（PKC）活性才能减弱AA的作用，这表明脂肪酸可能通过PKC依赖和PKC非依赖途径发挥作用。为了确定AA的代谢产物是否参与了归因于AA的效应，如果是，是哪些代谢产物，我们抑制了三种花生四烯酸代谢途径：用吲哚美辛（50微摩尔）抑制环氧化酶，用去甲二氢愈创木酸（NGDA，50微摩尔）抑制脂氧合酶，用5,8,11,14-二十碳四炔酸（ETYA，10微摩尔）抑制环氧合酶。NGDA和ETYA降低了AA对GH释放的作用（分别为50%和74%），并抑制了[Ca2+]i反应，而吲哚美辛则略微增强了AA诱导的GH释放和[Ca2+]i升高。由于这些结果表明脂氧合酶代谢产物可能是AA诱导的钙内流和GH释放的原因，我们测试了5-、12-和15-氢过氧二十碳四烯酸（5-、12-和15-HpETE）对[Ca2+]i和GH释放的影响。它们均以剂量依赖的方式刺激钙内流和GH释放，12-HpETE比5-和15-HpETE更有效。我们得出结论，花生四烯酸的脂氧合酶代谢产物，特别是12-HpETE，可能参与GH分泌机制，可能是通过促进钙经L型钙通道内流来实现的。
