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-) and prostaglandin E(2) (PGE(2)), products of NO synthase (NOS) and cyclooxygenase, respectively. Production of both, NO2- and PGE(2) by astrocytes, was inhibited by the exposure of the NOS inhibitor Nw-nitro-L-arginine methyl ester (L-NAME: 1, 10, and 100 mu M) in a dose related manner. Besides, other NOS inhibitors such as Nitro L-arginine (NNA: 10(-3) M) prevented the increase in PGE(2) release from LPS-stimulated astrocytes. Sodium nitroprusside (SNP; 100-200 mu M) used as a NO donor caused a dose-related enhancement in the accumulation of PGE(2) induced 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 addition, SNP also enhanced the synthesis of PGE(2) following exogenous arachidonic acid astrocytes exposure. Interestingly, this effect was blocked by indomethacin. Treatment of astrocytes cultures with dexamethasone (0.1, 1 mu M) blocked dose-relatedly the LPS-induced release of both 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 by astrocytes following exposure to LPS. These results strongly indicate that in astroglial cells, NO is able to activate the cyclooxygenase pathway. (C) 1995 Wiley-Liss, Inc.