Vol. 60, Issue 3, 421-426, September 2001

ACCELERATED COMMUNICATION
Induction of L-Arginine Transport Is Inhibited by Atrial Natriuretic Peptide: A Peptide Hormone as a Novel Regulator of Inducible Nitric-Oxide Synthase Substrate Availability

Alexandra K. Kiemer and Angelika M. Vollmar

Department of Pharmacy, Center of Drug Research, University of Munich, Munich, Germany

Background: The inducible nitric-oxide synthase (iNOS) synthesizes NO from L-arginine. Availability of L-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 of L-[³H]arginine. L-[³H]Arginine influx was also determined in LPS-activated cells in the presence of N^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 of L-ornithine. Results: ANP dose dependently (10⁸-10⁶M) inhibited LPS-induced L-[³H]arginine uptake when added simultaneously with LPS, whereas it showed no effect when added simultaneously with L-[³H]arginine. The effect was abrogated by the A-receptor antagonist HS-142-1 (10 µg/ml). CNP (10⁶ M) did not influence L-arginine transport. Competitor amino acids (10² M) inhibited L-[³H]arginine uptake. An excess of unlabeled L-arginine (10² M) as well as its analog L-NMMA (10³ 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.