Natriuretic peptides modulate nitric oxide synthesis in cytokine-stimulated cardiac myocytes

In patients with congestive heart failure, plasma atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) levels are frequently increased, but whether natriuretic peptides act directly on the heart has not been clarified. We investigated the effects of natriuretic peptides on nitric oxide (NO) synthase activity in cardiac myocytes. We measured the production of nitrite, a stable metabolite of nitric oxide, and the expression of inducible NO synthase (iNOS) mRNA and protein in cultured neonatal rat cardiac myocytes. Incubation of cardiac myocytes for 24 h with interleukin-1beta (IL-1beta) caused a significant increase in NO production. ANP, BNP and 8-bromo-cGMP, but not C-type natriuretic peptide (CNP), augmented NO synthesis in IL-1beta-stimulated cardiac myocytes in dose- and time-dependent manners. The same effects of ANP and BNP were observed at different doses of IL-1beta. Simultaneous incubation with IL-1beta in the presence of the NOS inhibitor NG-monomethyl-l-arginine or the RNA synthesis inhibitor actinomycin D for 24 h completely inhibited ANP- and BNP- as well as IL-1beta-induced nitrite production. ANP- BNP-induced NO synthesis in IL-1beta-stimulated cells were accompanied by increased iNOS mRNA and protein levels. The cGMP-dependent protein kinase inhibitor Rp-8-Br-cGMPS completely inhibited the effects of ANP and BNP. These findings indicate that both ANP and BNP up-regulate IL-1beta-induced iNOS expression in cardiac myocytes, which is at least partially mediated via activation of cGMP-dependent protein kinase.