We investigated whether arginase inhibition suppressed interleukin (IL)-1 beta-stimulated proliferation in vascular smooth muscle cells (VSMCs) and the possible mechanisms involved. IL-1 beta stimulation increased VSMC proliferation, while the arginase inhibitor BEC and transfection of the antisense (AS) oligonucleotide against arginase I decreased VSMC proliferation and was associated with increased protein content of the cell cycle regulator p21Waf1/Cip1. IL-1 beta incubation induced inducible nitric oxide synthase (iNOS) mRNA expression and protein levels in a dose-dependent manner, but did not affect arginase I and II expression. Consistent with this data, IL-1 beta stimulation resulted in increase in NO production that was significantly augmented by arginase inhibition. The specific iNOS inhibitor 1400W abolished IL-1 beta-mediated NO production and further accentuated IL-1 beta-stimulated cell proliferation. Incubation with NO donors GSNO and DETA/NO in the presence of IL-1 beta abolished VSMCs proliferation and increased p21Waf1/Cip1 protein content. Furthermore, incubation with the cGMP analogue 8-Br-cGMP prevented IL-1 beta-induced VSMCs proliferation. In conclusion, arginase inhibition augmented iNOS-dependent NO production that resulted in suppression of IL-1 beta-induced VSMCs proliferation in a cGMP-dependent manner. Crown Copyright (C) 2013 Published by Elsevier Inc. All rights reserved.