NOREPINEPHRINE STIMULATES ARACHIDONIC-ACID RELEASE FROM VASCULAR SMOOTH-MUSCLE VIA ACTIVATION OF CPLA(2)

The mechanism of agonist-activated arachidonate release was studied in segments of rat tail artery. Tail artery segments were prelabeled wit h [H-3]arachidonate and then stimulated with norepinephrine (NE), and the radioactivity of the extracellular medium was determined. NE stimu lated arachidonate release from the tissue without increasing arachido nic acid levels within cellular cytosol or crude membranes. About 90% of the extracellular radioactivity was shown to be unmetabolized arach idonate by TLC. Arachidonic acid release was not inhibited by the remo val of the endothelium from the artery. NE exerted a half-maximal effe ct at a concentration of 0.2 mu M. NE-stimulated arachidonate release was not inhibited by blockers of phospholipase C (U-73122), diacylglyc erol Lipase (RHC-80267), secretory phospholipase A(2) (manoalide), cal cium-insensitive phospholipase A(2) (HELSS), or beta-adrenergic recept ors (propranolol). NE-stimulated arachidonic acid release was inhibite d by blockers of cytosolic phospholipase A(2) (cPLA(2)) (AACOCF(3)), a lpha(1)-adrenergic receptors (prazosin), and specific G proteins (pert ussis toxin). This indicated that NE stimulated arachidonate release f rom vascular smooth muscle via activation of alpha(1)-adrenergic recep tors, either G(i) or G(o), and cPLA(2). NE-activated arachidonic acid release from vascular smooth muscle may play a role in force generatio n by the tissue. Perhaps arachidonic acid extends the effect of NE on one specific smooth muscle cell to its nearby neighbor cells.