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.

摘要

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 microg/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-[(3)H]arginine. L-[(3)H]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 (10(-8)-10(-6)M) inhibited LPS-induced L-[(3)H]arginine uptake when added simultaneously with LPS, whereas it showed no effect when added simultaneously with L-[(3)H]arginine. The effect was abrogated by the A-receptor antagonist HS-142-1 (10 microg/ml). CNP (10(-6) M) did not influence L-arginine transport. Competitor amino acids (10(-2) M) inhibited L-[(3)H]arginine uptake. An excess of unlabeled L-arginine (10(-2) M) as well as its analog L-NMMA (10(-3) M) also reduced L-[(3)H]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.