Studies on the mechanism for arachidonic acid liberation in mammalian cells with stimulus-response coupling

花生四烯酸作为类二十烷酸的前体被磷脂酶A_2 （PLA_2）水解膜磷脂释放。二酰基甘油（DAG）脂肪酶通过磷脂酶D （PLD）和磷脂磷酸水解酶（PAPase）的顺序作用产生花生四烯酸，本研究探讨了DAG在大鼠腹膜肥大细胞刺激后是否为重要途径。得到的结果如下：1。Ca^<2+>离子载体离子霉素刺激花生四烯酸释放后，通过添加乙醇抑制磷脂酸的产生（通过PLD激活）或抑制PAPase或DAG脂酶的抑制剂，花生四烯酸释放被抑制约50%。乙醇或上述抑制剂可完全抑制花生四烯酸对IgE受体依赖性刺激的释放。前列腺素d2 （PGD_2）是花生四烯酸在大鼠腹膜肥大细胞对IgE受体依赖性刺激和离子霉素反应的主要代谢物，可被乙醇或上述抑制剂完全抑制。蜂毒素刺激可特异性激活PLA_2，诱导花生四烯酸释放，但不产生PGD_2；而PLD刺激ADP核糖基化因子（ARF）可诱导显著的PGD_2产生和花生四烯酸释放，两者在乙醇存在下均被完全抑制。这些结果表明，在大鼠腹膜肥大细胞中，刺激诱导的花生四烯酸释放除了通过PLA_2途径外，还通过顺序的PLD/PAPase/DAG脂肪酶途径，而花生四烯酸释放后PGD_2的产生完全依赖于PLD相关的脂质代谢。

Arachidonic acid as a precursor for eicosanoid is known to be liberated by the hydrolytic action of phospholipase A_2 (PLA_2) on membrane phospholipids. The present study has been undertaken to investigate whether or not the arachidonic acid liberation by diacylglycerol (DAG) lipase from DAG which is produced through the sequential actions of phospholipase D (PLD) and phosphatidate phosphohydrolase (PAPase), is the important pathway upon stimulation in rat peritoneal mast cells. The results obtained are as follows.1. The arachidonic acid liberation upon stimulation with Ca^<2+> ionophore ionomycin was inhibited by about 50 % by addition of ethanol to suppress phosphatidic acid production through PLD activation, or of inhibitors for PAPase or DAG lipase.2. The arachidonic acid liberation in response to IgE receptor-dependent stimulation was completely inhibited by ethanol or the inhibitors indicated above.3. The production of prostaglandin D_2 (PGD_2), a major metabolite of arachidonic acid in rat peritoneal mast cell in response to IgE receptor-dependent stimulation and also ionomycin, was completely suppressed by ethanol or the inhibitors indicated above.4. Stimulation with melittin, that can specifically activate PLA_2, induced arachidonic acid liberation but not PGD_2 production, while stimulation with ADP ribosylation factor (ARF), that does PLD,induced marked PGD_2 production as well as arachidonic acid liberation both of which were completely suppressed in the presence of ethanol.These results indicate that in rat peritoneal mast cells stimulus-induced arachidonic acid liberation is contributed by the sequential PLD/PAPase/DAG lipase pathway in addition to PLA_2 pathway, whereas PGD_2 production following arachidonic acid liberation is fully dependent on the PLD-linked lipid metabolism.