Abstract

Background: The inducible nitric-oxide synthase (iNOS) synthesizes NO from l-arginine. Availability ofl-arginine is maintained by a lipopolysaccharide (LPS)-induced induction of the CAT-2B amino acids transporter. Recently, we could show that the cardiovascular hormone atrial natriuretic peptide (ANP) inhibits the induction of iNOS in LPS-stimulated macrophages via its guanylate cyclase-coupled A-receptor. Purpose: To investigate whether ANP exerts an effect on LPS-induced l-arginine uptake.Methods: Murine bone marrow derived macrophages were activated with LPS (1 μg/ml, 20 h) in the presence or absence of ANP or C-type natriuretic peptide (CNP). l-Arginine transport was determined by measuring the uptake ofl-[³H]arginine.l-[³H]Arginine influx was also determined in LPS-activated cells in the presence ofN^G-monomethyl-l-arginine (l-NMMA), competitor amino acids, or ANP. Nitrite accumulation was determined in supernatants of LPS-activated cells cultured in the presence or absence ofl-ornithine. Results: ANP dose dependently (10⁻⁸–10⁻⁶M) inhibited LPS-inducedl-[³H]arginine uptake when added simultaneously with LPS, whereas it showed no effect when added simultaneously withl-[³H]arginine. The effect was abrogated by the A-receptor antagonist HS-142–1 (10 μg/ml). CNP (10⁻⁶ M) did not influencel-arginine transport. Competitor amino acids (10⁻² M) inhibitedl-[³H]arginine uptake. An excess of unlabeled l-arginine (10⁻² M) as well as its analogl-NMMA (10⁻³ M) also reduced l-[³H]arginine influx. l-Arginine uptake was critical for production of NO because l-ornithine significantly decreased LPS-induced nitrite accumulation.Conclusion: This work demonstrates that ANP inhibits LPS-induced l-arginine uptake via its guanylate cyclase-coupled A-receptor. Besides its influence on the induction of iNOS, this effect may represent an important and unique mechanism by which ANP regulates NO production in macrophages.