Angiotensin II inhibits cytokine-stimulated inducible nitric oxide synthase expression in vascular smooth muscle cells

Abstract

In cultured vascular smooth muscle cells (VSMC), inflammatory cytokines such as interleukin 1 beta (IL-1 beta) and tumor necrosis factor alpha stimulated nitric oxide (NO) production via the expression of an inducible type of NO synthase (iNOS). A potent vasoconstrictor, angiotensin II (Ang II), which causes a rapid phospholipase C-mediated phosphoinositide hydrolysis via the Ang II type 1 (AT1) receptor in VSMC, by itself did not stimulate the production of nitrite, a stable metabolite of NO, but dose dependently inhibited the IL-1 beta-induced nitrite production. This inhibitory effect of Ang II was blocked by an AT1 receptor antagonist, CV-11974, but not by an Ang II type 2 receptor antagonist, PD 123319. The presence of Ang II during the early induction phase of iNOS was required for this inhibition. Consistently, Ang II suppressed IL-1 beta-induced increases in iNOS mRNA and protein levels. Ang II also inhibited increases in nitrite production and iNOS mRNA and protein levels caused by tumor necrosis factor alpha. A protein kinase C-activating phorbol ester, phorbol 12-myristate 13-acetate, and a membrane-permeable diacylglycerol, 1,2-dioctanoyl-glycerol, similarly inhibited the IL-1 beta-induced nitrite production and iNOS mRNA and protein expression, although repetitive additions were needed in the case of diacylglycerol. These results indicate that Ang II negatively modulates cytokine-induced NO production by blocking iNOS expression via the AT1 receptor in VSMC and suggest that protein kinase C could be involved in this process.