Arginine vasopressin increases nitric oxide synthesis in cytokine-stimulated rat cardiac myocytes.

We investigated the effects of arginine vasopressin (AVP) on nitric oxide (NO) synthase activity in cardiac myocytes by measuring the production of nitrite, a stable metabolite of NO, and the expression of inducible NO synthase (iNOS) mRNA and protein. Incubation of cultured neonatal rat cardiac myocytes for 24 hours with interleukin-1beta (IL-1beta) caused a significant increase in NO production. Both AVP and V1a receptor agonist [Phe2,Ile3,Orn8]vasopressin augmented NO synthesis in IL-1beta-stimulated, but not in unstimulated myocytes, in a dose-dependent manner. The V1a receptor antagonist [d(CH2)[5]1,O-Me-Tyr2,Arg8]vasopressin completely inhibited the effect of AVP. The AVP-induced NO production by IL-1beta-stimulated cells was accompanied by increased iNOS mRNA and protein accumulation. AVP caused a significant increase in cytosolic free Ca2+ levels of cardiac myocytes, whereas it showed no effect on cytosolic cAMP levels. After protein kinase C activity was functionally depleted by treating cells with phorbol 12-myristate 13-acetate for 24 hours, AVP did not augment IL-1beta-induced NO production. The effect of AVP was also inhibited in the presence of the protein kinase C inhibitor calphostin C. The addition of AVP increased protein kinase C activity in cardiac myocytes, and its effect was significantly inhibited in the presence of calphostin C. These results support the hypothesis that the heart may be a target organ for AVP and that AVP modulates IL-1beta-induced iNOS expression in myocytes through the V1a receptor, which is mediated at least partially via activation of protein kinase C.