NITRIC-OXIDE SYNTHESIS IN CARDIAC MYOCYTES AND FIBROBLASTS BY INFLAMMATORY CYTOKINES

Objective: The aim was to investigate nitric oxide (NO) synthase activ ity in cultured neonatal rat cardiac myocytes and fibroblasts upon tre atment with inflammatory cytokines interleukin 1 beta (IL-1 beta), tum our necrosis factor alpha (TNF-alpha), IL-2, IL-6, IL-8, transforming growth factor beta (TGF-beta) and gram negative bacterial lipopolysacc haride (LPS). Methods: NO and guanosine 3',5'-cyclic monophosphate (cG MP) synthesis was measured in cultured neonatal rat cardiac myocytes a nd fibroblasts, using Griess reagent and an enzyme immunoassay kit, re spectively. The expression of inducible NO synthase (iNOS) mRNA and pr otein was assayed by northern and western blotting, respectively. Resu lts: Incubation of cardiac myocytes for 24 h with IL-1 beta (10 ng . m l(-1)) or LPS (1 mu g . ml(-1)) caused significant increases in NO and cGMP production. TNF-alpha, IL-2, IL-6, IL-8, and TGF-beta showed no significant effect on their production. IL-1 beta induced NO and cGMP production in a time and dose dependent manner. IL-1 beta also increas ed iNOS mRNA and protein accumulation in cardiac myocytes. Simultaneou s incubation of IL-1 beta with N-G-monomethyl-L-arginine, genistein, c alphostin C, cycloheximide, or actinomycin D completely inhibited the IL-1 beta induced NO production by cardiac myocytes. TGF-beta, dexamet hasone, or cyclosporin A also dose dependently inhibited the IL-1 beta induced NO production. Exposure to IL-1 beta for 12-24 h decreased th e beating rate of cardiac myocytes, but addition of dexamethasone comp letely overcame this inhibition. In contrast to cardiac myocytes, incu bation of cardiac fibroblasts for 24 h with IL-1 beta or LPS showed no significant effect on NO or cGMP production. Conclusions: These obser vations suggest that IL-1 beta/LPS responsive iNOS, which is an import ant regulator of contractile function of the heart, is present in card iac myocytes but not in cardiac fibroblasts.