DISSOCIATION OF LIPOPOLYSACCHARIDE-MEDIATED INDUCTION OF NITRIC-OXIDESYNTHASE AND INHIBITION OF DNA-SYNTHESIS IN RAW-264.7 MACROPHAGES ANDRAT AORTIC SMOOTH-MUSCLE CELLS

1 The active component of endotoxin, lipopolysaccharide (LPS), inhibit ed basal DNA synthesis in both RAW 264.7 macrophages (IC50 0.05 +/- 0. 03 mu g ml(-1)) and rat aortic smooth muscle cells (RASMC) (IC50 9.7 /- 0.4 mu g ml(-1)). 2 In both cell types, serum differentially affect ed LPS-stimulated inhibition of DNA synthesis. In RAW 264.7 macrophage s the presence of serum reduced the IC50 for LPS-stimulated inhibition of DNA synthesis (1.4 +/- 0.85 ng ml(-1)). However, in RASMC serum st imulated DNA synthesis and further increased the IC50 value for LPS-st imulated inhibition of thymidine incorporation (57.3 +/- 7.8 mu g ml(- 1)). 3 LPS also stimulated the induction of nitric oxide synthase (NOS ) in RAW 264.7 macrophages with maximal expression at concentrations o f 1-3 mu g ml(-1). This was wholly dependent upon the presence of seru m. In RASMC LPS alone, up to concentrations of 100 mu g ml(-1), did no t induce nitric oxide synthase and required co-incubation with the dir ect activator of adenylyl cyclase, forskolin. Under these conditions s timulated expression of NOS was inhibited by the presence of serum. 4 Incubation with the nitric oxide synthase inhibitors N-omega-nitro-L-a rginine methyl ester (L-NAME) and L-canavanine did not reverse the inh ibition of [H-3]-thymidine incorporation in response to LPS but preven ted the formation of nitrite in both cell types. 5 These results indic ate that the effects of LPS upon cell growth are independent of the in duction of the 130 kDa isoform of nitric oxide synthase and nitric oxi de formation in both RAW 264.7 macrophages and RASMC.