Inhibition of nitric oxide synthase abrogates lipopolysaccharides-induced up-regulation of L-arginine uptake in rat alveolar macrophages

1 It was tested whether the inducible nitric oxide synthase (iNOS) pathway might be involved in lipopolysaccharides-(LPS)-induced up-regulation of L-a rginine transport in rat alveolar macrophages (AM Phi). 2 AM Phi were cultured in absence or presence of LPS. Nitrite accumulation was determined in culture media and cells were used to study [H-3]-L-argini ne uptake or to isolate RNA for RT-PCR. 3 Culture in presence of LPS (1 mug ml(-1), 20 h) caused II fold increase o f nitrite accumulation and 2.5 fold increase of [H-3]-L-arginine uptake. 4 The inducible NO synthase (iNOS) inhibitor 2-amino-5,6-dihydro-6-methyl-4 H-1,3-thiazine (AMT) present alone during culture had only marginal effects on [H-3]-L-arginine uptake. However, AMT present during culture additional ly to LPS, suppressed LPS-induced nitrite accumulation and LPS-stimulated [ H-3]-L-arginine uptake in the same concentration-dependent manner. AMT pres ent only for the last 30 min of the culture period had similar effects on [ H-3]-L-arginine uptake. AMT present only during the uptake period also inhi bited LPS-stimulated [H-3]-L-arginine uptake, but with lower potency. 5 The inhibitory effect of AMT could not be opposed by the NO releasing com pound DETA NONOate. 6 LPS caused an up-regulation of the mRNA for the cationic amino acid trans porter CAT-2B, and this effect was not affected by AMT. 7 AMT (100 muM) did not affect L-arginine transport studied by electrophysi ological techniques in Xenopus laevis oocytes expressing either the human c ationic amino acid transporter hCAT-1 or hCAT-2B. 8 In conclusion, iNOS inhibition in rat AM Phi abolished LPS-activated L-ar ginine uptake. This effect appears to be caused by reduced Bow of L-arginin e through the iNOS pathway. British Journal of Pharmacology (2001).