Cultured astrocytoma cells generate a nitric oxide‐like factor from endogenous L‐arginine and glyceryl trinitrate: effect of E. coli lipopolysaccharide

The inhibitory activity of astrocytoma cells (0.25–3 × 105) treated with indomethacin (10 μm) on platelet aggregation was enhanced by incubating the cells with E. coli lipopolysaccharide (LPS, 0.5 μg ml−1) for 18 h. This effect was attenuated when cycloheximide (10 μg ml−1) was incubated together with LPS. The inhibition of platelet aggregation by cells treated with LPS was potentiated by superoxide dismutase (60 u ml−1) and ablated by oxyhaemoglobin (oxyHb, 10 μm) or NG‐monomethyl‐l‐arginine (l‐NMMA, 30–300 μm). The effects of l‐NMMA were reversed by co‐incubation with l‐arginine (l‐Arg, 100 μm) but not d‐arginine (d‐Arg, 100 μm). LPS also increased the levels of nitrite in the culture media and this increase was ablated by co‐incubation with l‐NMMA (300 μm) or cycloheximide (10 μg ml−1). Astrocytoma cells (0.5 × 105) treated with indomethacin (10 μm) enhanced the platelet inhibitory activity of glyceryl trinitrate (GTN, 11–352 μm) but not that of sodium nitroprusside (4 μm). Furthermore, when incubated with GTN (200 μm) a 4 fold increase in the levels of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) was observed. These effects were abrogated by co‐incubation with oxyHb (10 μm) but not with l‐NMMA (300 μm). Treatment of the cells with LPS (0.5 μg ml−1) for 18 h did not enhance their capacity to form NO from GTN. Thus, in cultured astrocytoma cells, LPS enhances the formation of nitric oxide from endogenous l‐arginine. In addition, these cells can metabolize GTN to nitric oxide but this process is not enhanced by LPS stimulation. 1992 British Pharmacological Society