Differential regulation of nitric oxide production by increase of intracellular cAMP in murine primary fibroblasts and L929 fibrosarcoma cell line

The effect of intracellular cAMP rise on nitric oxide (NO) production was c ompared in murine primary fibroblasts isolated from the spleens of CBA mice , and L929 fibrosarcoma cell line. Treatment of confluent L929 cells with c AMP analogues -dibutyryl-cAMP (db-cAMP) or 8-Cl-cAMP caused dose-dependent augmentation of inducible NO synthase (iNOS)-mediated NO production, which has been abrogated by inhibition of protein synthesis with cycloheximide or addition of selective iNOS inhibitor aminoguanidine. In contrast, under th e same cultivating conditions, cAMP analogues were not able to upregulate N O synthesis in primary fibroblasts. Treatment with cAMP analogues or non-se lective phosphodiesterase (PDE) inhibitor pentoxifylline affected IFN gamma -induced NO synthesis in both cell types, but in the opposite manner-enhanc ing in L929 cells and suppressive in primary fibroblasts. The induction of iNOS, but not its catalytic activity, was impaired in cAMP-treated primary fibroblasts. Finally, PDE type IV inhibitor rolipram enhanced IFN-gamma-tri ggered NO synthesis in L929 cells, but was unable to mimic cAMP analogue or PTX-mediated suppression of NO synthesis in spleen fibroblasts. These resu lts suggest that, in contrast to L929 fibrosarcoma cell line, intracellular cAMP rise might have a role in downregulation of NO production in murine p rimary fibroblasts. (C) 2000 Elsevier Science B.V. All rights reserved.