Prostacyclin formation elicited by endothelin-1 in rat aorta is mediated via phospholipase D activation and not phospholipase C or A2.

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that also stimulates production of prostacyclin (PGI2) from arachidonic acid. The purpose of this study was to determine the contribution of phospholipases (PLs) A2, C, and/or D in ET-1-induced PGI2 formation in the rat aorta, measured as immunoreactive 6-ketoprostaglandin (PG) F1 alpha. ET-1 increased 6-keto-PGF1 alpha formation, which was not affected by a PLA2 inhibitor, 7,7-dimethyl eicosadienoic acid (DEDA). Furthermore, ET-1 failed to stimulate PLA2 activity measured in the cytosol (cPLA2), using phosphatidylcholine, L-a-1-palmitoyl-2-arachidonyl[14C] as a substrate. However, the adrenergic agonist norepinephrine increased 6-keto-PGF1 alpha formation, which was attenuated by DEDA, and enhanced PLA2 activity. ET-1 enhanced PLC activity, as indicated by increased inositol phosphate production, which was prevented by a PLC inhibitor, U-73122. However, ET-1-induced 6-keto-PGF1 alpha production was not altered by U-73122. An inhibitor of PLD activation, C2-ceramide, attenuated ET-1-induced PLD activity, as indicated by the production of phosphatidylethanol. Furthermore, ET-1-induced 6-keto-PGF1 alpha formation was inhibited by C2-ceramide as well as by ethanol treatment. Moreover, inhibitors of phosphatidate phosphohydrolase (propranolol) and diacylglycerol lipase (RHC-80267), attenuated ET-1-induced 6-keto-PGF1 alpha formation. Finally, ET-1-induced activation of PLD was not attenuated by a selective PKC inhibitor, bisindolylmaleimide I. These data suggest a novel pathway for ET-1-induced PGI2 formation in the rat aorta involving activation of PLD but not cPLA2 and independent of PLC or PKC activation.