Angiotensin II Augments Cytokine-Stimulated Nitric Oxide Synthesis in Rat Cardiac Myocytes

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Abstract
Background Nitric oxide (NO) has been shown to modulate cardiac function. We investigated the effect of angiotensin II (Ang II) on NO synthase activity in cardiac myocytes. Methods and Results Using the Griess reagent, we measured the production of nitrite, a stable metabolite of NO, by cultured neonatal rat cardiac myocytes. The expression of inducible NO synthase (iNOS) mRNA was assayed by Northern blotting. Incubation of cardiac myocytes for 24 hours with interleukin-1β (IL-1β) caused a significant increase in NO production. Ang II significantly augmented NO synthesis in IL-1β–stimulated but not in unstimulated cells in a dose-dependent manner. The angiotensin type I receptor antagonist CV 11974 inhibited the effect of Ang II dose-dependently. Simultaneous incubation of Ang II with N G -monomethyl- l -arginine or actinomycin D also completely inhibited the effect of Ang II. The Ang II–induced NO production by IL-1β–stimulated cells was accompanied by increased iNOS mRNA accumulation. Phorbol 12-myristate 13-acetate (PMA) also augmented NO synthesis in IL-1β–stimulated but not in unstimulated cells in a dose-dependent manner. The protein kinase C inhibitor calphostin C dose-dependently blocked the effect of Ang II. After protein kinase C activity was functionally depleted by treatment of cells with PMA for 24 hours, Ang II did not augment IL-1β–induced NO production. Conclusions These results indicate that Ang II upregulates IL-1β–induced iNOS expression in cardiac myocytes, which is mediated at least partially via activation of protein kinase C.