EVIDENCE FOR CYCLOOXYGENASE ACTIVATION BY NITRIC-OXIDE IN ASTROCYTES

We have evaluated the role of nitric oxide (NO) on the cyclooxygenase pathway in mouse glial cells. Exposure of primary cultures of neonatal mouse cortical astrocytes to bacterial lipopolysaccharide (LPS; 1 mu g/ml, 18 h) caused an increase in the release of both nitrite (NO2-) a nd prostaglandin E(2) (PGE(2)), products of NO synthase (NOS) and cycl ooxygenase, respectively. Production of both, NO2- and PGE(2) by astro cytes, was inhibited by the exposure of the NOS inhibitor Nw-nitro-L-a rginine methyl ester (L-NAME: 1, 10, and 100 mu M) in a dose related m anner. Besides, other NOS inhibitors such as Nitro L-arginine (NNA: 10 (-3) M) prevented the increase in PGE(2) release from LPS-stimulated a strocytes. Sodium nitroprusside (SNP; 100-200 mu M) used as a NO donor caused a dose-related enhancement in the accumulation of PGE(2) induc ed by LPS and the presence of hemoglobin blocked the SNP effects. The exposure to SNP counteracted the decrease of PGE(2) production in LPS- treated astrocytes in which NO synthesis was blocked by L-NAME. In add ition, SNP also enhanced the synthesis of PGE(2) following exogenous a rachidonic acid astrocytes exposure. Interestingly, this effect was bl ocked by indomethacin. Treatment of astrocytes cultures with dexametha sone (0.1, 1 mu M) blocked dose-relatedly the LPS-induced release of b oth NO2- and PGE(2). As expected, the presence of indomethacin (1, 10, and 20 mu M) prevented in a dose related fashion, PGE(2) production b y astrocytes following exposure to LPS. These results strongly indicat e that in astroglial cells, NO is able to activate the cyclooxygenase pathway. (C) 1995 Wiley-Liss, Inc.