Antimitogenic actions of organic nitrates are potentiated by sildenafil and mediated via activation of protein kinase A

Migration and proliferation of vascular smooth muscle cells (SMC) in response to platelet-derived growth factor (PDGF) and other mitogens play an important role in restenosis after coronary angioplasty. Elevation of both cAMP and cGMP has been shown to inhibit SMC mitogenesis. The aim of this study was to examine the antimitogenic actions of organic nitrates and sildenafil and to clarify the role of cyclic nucleotide-dependent protein kinases (PKA, PKG) in this action. Organic nitrates [glycerol trinitrate (GTN), isosorbide 5'-mononitrate (ISMN), pentaerythrityl-tetranitrate (PETN)] and the PDE5 inhibitor sildenafil reduced PDGF-induced DNA synthesis, measured by (H-3] thymidine incorporation. GTN, ISMN, and PETN acted synergistically with sildenafil (1 muM) on inhibition of PDGF-induced DNA synthesis, increase of intracellular cyclic nucleotides, and vasodilator-stimulated phosphoprotein phosphorylation. The highly selective PKA inhibitor PKI abolished these actions of sildenafil and organic nitrates, whereas the PKG inhibitors KT5823 and (Rp)-8-pCPT-cGMPS had no effect. In addition, selective activation of PKG without inhibition of PDE3 by the cGMP analog 8-pCPT-cGMP (100 muM) had no antimitogenic effect. The data suggest that 1) organic nitrates and sildenafil exert antimitogenic actions by activation of PKA via inhibition of PDE3, but not by activation of PKG and 2) that antimitogenic effects of organic nitrates are potentiated by sildenafil at therapeutic plasma levels.