COMPARISON OF THE EFFECTS OF NITRIC-OXIDE AND PEROXYNITRITE ON THE 12-LIPOXYGENASE AND CYCLOOXYGENASE METABOLISM OF ARACHIDONIC-ACID IN RABBIT PLATELETS

The effects of a new type of nitric oxide (NO)-releasing compound, oxo -3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene (NOC7), and peroxynitr ite (ONOO-) on the formation of 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), thromboxane (TX) B-2 and 12-hydroxy-5,8,10-heptadecatr ienoic acid (HHT) from exogenous arachidonic acid in washed rabbit pla telets have been compared. At concentrations of 5 mu M and below, NOC7 inhibited 12-HETE formation (56.5-98.8% inhibition). Moreover, NOC7 i nhibited TXB2 and HHT formation at concentrations ranging from 5 to 20 mu M (TXB2, 62.2-88.1% inhibition; HHT, 11.6-62.2% inhibition). ONOO- had little or no effect on the production of these three metabolites at concentrations of up to 50 mu M. Experiments utilizing a new class of NO antidote, oxy-2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-o xide, revealed that the observed effects of NOC7 are caused by NO. The effects of NO were reversed by addition of the superoxide generating system (xanthine plus xanthine oxidase and catalase), indicating that superoxide is a vital modulator of the action of NO. These results sug gest that NO, but not ONOO- (up to 50 mu M), can be a potent dual inhi bitor of the 12-lipoxygenase and cyclooxygenase activities in platelet s and that superoxide is an important regulator of the action of NO.