CYTOCHROME-P-450 METABOLITES MEDIATE NOREPINEPHRINE-INDUCED MITOGENICSIGNALING

Norepinephrine (NE) stimulates release of arachidonic acid (AA) from t issue lipids in blood vessels, which is metabolized via cyclooxygenase , lipoxygenase (LO), and cytochrome P-450 (CYP-450) pathways to biolog ically active products. Moreover, NE and AA have been shown to stimula te proliferation of vascular smooth muscle cells (VSMCs) of rat aorta. The purpose of this study was to determine the possible contribution of AA and its metabolites to NE-induced mitogenesis in VSMCs of rat ao rta and the underlying mechanism of their actions, NE (0.1 to 10 mu mo l/L) increased DNA synthesis as measured by [H-3]thymidine incorporati on in VSMCs, and this effect was attenuated by inhibitors of CYP-450 ( 17-octadecynoic acid, 5 mu mol/L; 12-diabromododec-11-enoic acid, 10 m u mol/L; and dibromo-dodecenyl-methylsulfimide, 10 mu mol/L) and by th e LO inhibitor (baicalein, 20 mu mol/L), but not by the cyclooxygenase inhibitor (indomethacin, 5 mu mol/L). CYP-450 and LO metabolites of A A, 20-hydroxyeicosatetraenoic acid (HETE) (0.1 to 0.5 mu mol/L) and 12 (S)-HETE, respectively, increased [H-3]thymidine incorporation in VSMC s, Both NE and 20-HETE increased mitogen activated protein (MAP) kinas e activity as measured by the in-gel kinase assay. The inhibitor of MA P kinase kinase, PD-98059 (50 mu mol/L), attenuated NE as well as 30-H ETE induced [H-3]thymidine incorporation and MAP kinase activation in VSMCs. These data suggest that products of AA formed via CYP-450, most likely 20-HETE, and via LO mediate NE induced mitogenesis in VSMCs.