α-Adrenergic Stimulation Enhances Inducible Nitric Oxide Synthase Expression in Rat Cardiac Myocytes

We investigated the effects ofα1-adrenergic stimulation on nitric oxide (NO) production by cardiac myocytes. Incubation of cultured neonatal rat cardiac myocytes with interleukin-1β(IL-1β) caused a significant increase in the production of nitrite, a stable metabolite of NO. Addition of phenylephrine significantly augmented nitrite production by IL-1β-stimulated but not by unstimulated myocytes in a dose-dependent manner. The effect of phenylephrine was completely abolished in the presence of NG-monomethyl-L-arginine (L-NMMA) or actinomycin D. Northern blotting revealed increased inducible NO synthase mRNA accumulation in cardiac myocytes treated with IL-1βand phenylephrine compared with those treated with IL-1βalone. After protein kinase C activity was functionally depleted by treating cells with phorbol 12-myristate 13-acetate for 24 h, phenylephrine did not augment IL-1β-induced NO production. The effect of phenylephrine was also abolished in the presence of protein kinase C inhibitor calphostin C. These observations suggest thatα1-adrenergic stimulation causes an upregulation of cytokine-induced NO production by cardiac myocytes, which is mediated at least partially via activation of protein kinase C.