MECHANISM OF ANGIOTENSIN-II-INDUCED ARACHIDONIC-ACID METABOLITE RELEASE IN AORTIC SMOOTH-MUSCLE CELLS - INVOLVEMENT OF PHOSPHOLIPASE-D

In a previous study, we have shown that angiotensin IT (Ang II) activa tes phosphatidylcholinehydrolyzing phospholipase D due to Ang II-induc ed Ca2+ influx from extracellular space in subcultured rat aortic smoo th muscle cells, In the present study, we have investigated the role o f phospholipase D in Ang II-induced arachidonic acid (AA) metabolite r elease and prostacyclin synthesis in subcultured rat aortic smooth mus cle cells. Ang II significantly stimulated Aii metabolite release in a concentration-dependent manner in the range between 1 nmol/l and 0.1 mu mol/l. D.L-Propranolol hydrochloride (propranolol), an inhibitor of phosphatidic acid phosphohydrolase, significantly inhibited the Ang I I-induced release of AA metabolites. The Ang II-induced AA metabolite release was reduced by chelating extracellular Ca2+ with EGTA. Geniste in, an inhibitor of protein tyrosine kinases, significantly suppressed the Ang II-induced AA metabolite release. 1,6-Bis-(cyclohexyloximinoc arbonylamino)-hexane (RHC-80267), a potent and selective inhibitor of diacylglycerol lipase, significantly inhibited the Ang II-induced AA m etabolite release. Both propranolol and RHC-80267 inhibited the Ang II -induced synthesis of 6-keto-prostaglandin F-1 alpha, a stable metabol ite of prostacyclin. The synthesis was suppressed by genistein. These results strongly suggest that the AA metabolite release induced by Ang IT is mediated, at least in part, through phosphatidylcholine hydroly sis by phospholipase D activation in aortic smooth muscle cells.